Re: [time-nuts] WWVB BPSK Receiver Project?

[michael batchelor]

OK,  John Forster and I have been kicking around a few things off line, and he 
suggested I should bring part of it back on line. Maybe I have a few details 
wrong, or maybe I have them right and some folks are unaware of them.

My concern about the BPSK, and breaking my Spectracom oscillator, is really 
centered on loosing my NIST traceable reference oscillator. I don't care one 
bit what time of day it is.

I wrote:
>> I did poke around a bit, and it appears that WWVB is still an approved

>> frequency standard, so any oscillator which is phased locked to WWVB 
>> qualifies as an "NIST traceable" standard
>> reference oscillator, which is my only concern.

John wrote:
>Good news! Thanks.

I wrote:
>> A GPS disciplined oscillator, regardless of how stable/accurate it may be, 
>> is 
>> not an NIST traceable standard unless NIST decides to certify the Naval 
>> Observatory as a standard. Or I suppose NIST could take over the GPS 
>> correction uploads.but I don't see that happening any time soon. That's 
>> really outside their mission boundary.


Maybe a few things have changed in the metrology world in past few years, but 
the 
GPS based oscillators are controlled by the Naval Observatory clocks, not the 
NIST clocks. So while an HP-117 or a Spectracon 8160 oscillator phase locked to 
WWVB is "by definition" an NIST traceable standard so long as it is in lock and 
you have a valid lock history, a GPS unit, even though it may be just as stable 
an 
oscillator, isn't an NIST traceable standard without a whole lot of equipment to
validate that NIST and the GPS system are in sync. 

(There is/was actually a commercial solution to verify this, but it 
isn't/wasn't cheap.)

For all you metrology guys out there, has any of this recently changed? 

So my interest in keep my Spectracom going isn't just to keep a "stable" 10 MHz
oscillator in the lab. The GPS will give me a stable signal. My interest is in 
keeping 
a "stable and "traceable" 10 MHz signal going. After all, all our old gray-hair 
tax 
dollars paid for this government service over the past 5 decades. Why should we 
get kicked off the bus now? It isn't like we want anything new. Just don't 
break 
what we've already paid for. 

Michael
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Re: [time-nuts] WWVB BPSK Receiver Project?

[Ben Gamari]

Looks like this bounced as I sent from the wrong address. Better late
than never.

On Wed, 14 Mar 2012 15:46:48 -0700, Chuck Forsberg WA7KGX N2469R 
 wrote:
> Asus has a $30 Xonar PCI soundcard that should do the job.
> I have two of the the more expensive  pci-e versions.  Some motherboards
> can do a/d at 192 but not as well as the Xonar.
>
Even better: a USB DVB card [1]. For $30 you have a few million 8-bit
I/Q samples per second and an interface to Gnu Radio. The possibilities
are nearly endless.

Cheers,

- Ben

[1] http://sdr.osmocom.org/trac/wiki/rtl-sdr


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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[ehydra]

gary schrieb:
Just meditating out loud, if you were to go push pull with a ferrite 
antenna AND you are winding it yourself, you could avoid the biasing 
resistors by putting a center tap in the antenna itself, then tie that 
center tap to an appropriate bias voltage. I haven't seen this done, so 
their may be a gotcha with that scheme, but the science is good. 


Works with SA602. A russian web-site shows differential turns on a 
ferrite rod. 



Generally you will get a lower noise circuit if the input device is an 
amplifier rather than a buffer.


Yep.




Lanksford's input stage is essentially a push pull buffer, but I don't 
see that cancelling 2nd harmonics like a push pull amp. But for a whip, 
which is a single ended input, I don't see a way to get a differential 
input. Not true for a ferrite antenna.


You can transformer couple the input. Then the whip is at DC and it is 
possible to let DC-current to ground. 


- Henry


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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <4f669a4d.3010...@lazygranch.com>, gary writes:

>DC in a transformer raises the low frequency corner a bit. Obviously not 
>a problem in your case.

I just double-checked, because that rang a bell.  I did reinstate
the capacitors as 2.2uF films in the final article for exactly that
reason.

As for gain, I have never missed any, I get a good healthy signal,
even though I do live in the middle of a pop 30k city.

>I should point out that every active device Lankford puts in the signal 
>chain [...]

Why are you talking about Lankford at this point ?

What I built was Fig 5 from this:


http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf

I realize that Chris Trask started out from Lankfords design, but I don't
think it is fair to attribute the Fig 5 schematic to Lankford any more.

There's a picture of my implementation here:

http://phk.freebsd.dk/misc/ChrisTraskAntenna.jpg

I feed it 15 volts on the twinax pair, pull that out of the toroids
centertap, regulated it with a 12V 3-terminal.

You can see the prototype in the top right corner.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Poul-Henning Kamp]

In message <595370411-1332118092-cardhu_decombobulator_blackberry.rim.net-18097
4826-@b1.c24.bise6.blackberry>, shali...@gmail.com writes:

>I was not concerned about processing power on a PC (or Mac for
>that matter) but for the uC that was used in PHK's project.

That was sort of the entire point about the "aducLoran": to show that
for time-nuttery, you don't need much CPU.

If you wanted to extract a real-time modulation of any kind, the situation
is very different, but as long as you just want to extract a carrier
phase/frequency, averaging is the way to go and that is cheap.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

DC in a transformer raises the low frequency corner a bit. Obviously not 
a problem in your case.


I should point out that every active device Lankford puts in the signal 
chain adds noise since the amp is really just a buffer, not an 
amplifier. You really want front end gain so that devices after the gain 
stage do not add as much to the noise floor. It is input referred noise 
that is significant, and Lankford's design is terrible in this respect. 
Oops, I almost started that pissing contest. ;-)



On 3/18/2012 11:44 AM, Poul-Henning Kamp wrote:

In message<20120318182440.7cb729c2b018b0b2ca5f9...@kinali.ch>, Attila Kinali w
rites:

On Sun, 18 Mar 2012 13:25:54 +



Not in my implementation, I have eliminated the input capacitor because
the active element is 3cm from the PCB,


Could you explain how the distance of the antenna to the PCB is related
to a DC block capacitor? And how do you block current flowing from the
input stage of your amplifier into the antenna?


The input to the amplifier is just a piece of metal, there is no need
for a capacitor in series with it.

The output from the amplifier goes to a transformer which drives a piece
of "twin-ax" cable back to my lab.

The reason for the transformer is that to go really deep in frequency
the usual choke to separate the DC supply from RF signal doesn't work.

I the 'cable-side' of the transformer, in both ends, is centertapped
and that's how I provide power to the antenna.

I have successfully received the Russian "Omega-like" system at
9-15 kHz and I have detected but not demodulated the 86Hz submarine
transmission.

That's DC enough for me :-)



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Re: [time-nuts] WWVB BPSK Receiver Project?

[shalimr9]

I was not concerned about processing power on a PC (or Mac for that matter) but 
for the uC that was used in PHK's project.

Didier KO4BB


Sent from my BlackBerry Wireless thingy while I do other things...

-Original Message-
From: Chris Albertson 
Sender: time-nuts-boun...@febo.com
Date: Thu, 15 Mar 2012 15:48:41 
To: Discussion of precise time and frequency measurement
Reply-To: Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] WWVB BPSK Receiver Project?

On Thu, Mar 15, 2012 at 3:13 PM, Poul-Henning Kamp  wrote:
> In message <20120315152620.8347488e049854218aed4...@kinali.ch>, Attila Kinali 
> w
> rites:
>
>>> Do you need 16 bits or can you get by with a 12 bit ADC?
>
> In general: The more the merrier, for a digital dude like me, having
> more bits is easier than getting AGC working correctly :-)
>
>>> Have you considered using an FPGA for signal processing? It seems
>> you need a fairly serious CPU to handle that much data.


"That much data" we are talking about 192K samples per second.   I can
routinely record multiple tracks of 192K audio and do processing in
real time and the CPU meter hardly moves  the bottom.Even a
gigabit per second Ethernet port is not "a lot of data" on a modern
computer.

FPGAs and DSP come into play if you are talking about tens of millions
of samples per second with data rates above say 200Mb/Sec  But the
rate from an audio interface running 192K and 24-bits is still under
one megabyte per second.An interesting ratio is the number of CPU
cycles available to process one sample.  On my Apple iMac that would
be about roughly  200,000 operations per data sample.

In real life SDR receivers even an older CPU can process the I and Q
channels and maintain a large graphic screen and send and receive data
over a network and still not be "maxed out"


Chris Albertson
Redondo Beach, California

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <20120318182440.7cb729c2b018b0b2ca5f9...@kinali.ch>, Attila Kinali w
rites:
>On Sun, 18 Mar 2012 13:25:54 +

>> Not in my implementation, I have eliminated the input capacitor because
>> the active element is 3cm from the PCB,
>
>Could you explain how the distance of the antenna to the PCB is related
>to a DC block capacitor? And how do you block current flowing from the
>input stage of your amplifier into the antenna?

The input to the amplifier is just a piece of metal, there is no need
for a capacitor in series with it.

The output from the amplifier goes to a transformer which drives a piece
of "twin-ax" cable back to my lab.

The reason for the transformer is that to go really deep in frequency
the usual choke to separate the DC supply from RF signal doesn't work.

I the 'cable-side' of the transformer, in both ends, is centertapped
and that's how I provide power to the antenna.

I have successfully received the Russian "Omega-like" system at
9-15 kHz and I have detected but not demodulated the 86Hz submarine
transmission.

That's DC enough for me :-)

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Bruce Griffiths]

ehydra wrote:

I wonder because ALL of the shown circuits in his pdf are AC-coupled.
It is maybe possible to servo-loop with OpAmps but surely not worth 
the effort.


Useful too as a Scope FET-probe.



Not really the gain inaccuracy is somewhat excessive.
One can do much better with the right circuit.
The AC coupling between input and output stages isnt actually necessary 
if the output stage is biased appropriately.

A higher supply voltage also helps.

- Henry


Bruce

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

My choice would be a center tapped, shielded, air core loop, running into
a low noise instrumentation amp. Center tap of loop to twinax shield,
grounded at preamp.

The instrumentation amp has fixed gain, and very high CMRR and PSRR. It
also does the differential to single ended conversion properly and has a
low output impedance.


I have used an instrumentation amp in my breadboard, however, without 
center tapping and shielding. But it seemed to me to be a very good 
component for such low frequencies.



Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[J. Forster]

I'd not use a vertical antenna at all. Far too prone to EMI.

My choice would be a center tapped, shielded, air core loop, running into
a low noise instrumentation amp. Center tap of loop to twinax shield,
grounded at preamp.

The instrumentation amp has fixed gain, and very high CMRR and PSRR. It
also does the differential to single ended conversion properly and has a
low output impedance.

YMMV.

-John





> The circuit in question doesn't appear to be in the PDF. You need to use
> a lot of caution with Lankford's theories. I don't want to get into a
> pissing contest, so I will leave it at that.
>
> Push pull with transformers goes back to the tube days. It is a
> convenient scheme to kill 2nd harmonic distortion while at the same time
> biasing the single sex amplifier.
>
> Take the center tap and tie it to a positive voltage. Feed the other two
> inputs to the transformer with a differential signal. You have blocked
> DC from the output, restoring a ground referenced single phase. (as
> opposed to differential) output.
>
> These active whips are prone to picking up electrical noise. Fine if you
> live in the boonies. Not so good for urban dwellers.
>
> If the antenna is just a wire in the air, I'm not sure what good it does
> to capacitively couple the input. Who cares if some DC is floating on a
> wire just poking in the air.
>
> While some people think of transformers are bandlimiting devices, note
> that all those coupling caps have series inductance. There is no free
> lunch.
>
> Just meditating out loud, if you were to go push pull with a ferrite
> antenna AND you are winding it yourself, you could avoid the biasing
> resistors by putting a center tap in the antenna itself, then tie that
> center tap to an appropriate bias voltage. I haven't seen this done, so
> their may be a gotcha with that scheme, but the science is good.
> Generally you will get a lower noise circuit if the input device is an
> amplifier rather than a buffer.
>
> Lanksford's input stage is essentially a push pull buffer, but I don't
> see that cancelling 2nd harmonics like a push pull amp. But for a whip,
> which is a single ended input, I don't see a way to get a differential
> input. Not true for a ferrite antenna.
>
>
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

The circuit in question doesn't appear to be in the PDF. You need to use 
a lot of caution with Lankford's theories. I don't want to get into a 
pissing contest, so I will leave it at that.


Push pull with transformers goes back to the tube days. It is a 
convenient scheme to kill 2nd harmonic distortion while at the same time 
biasing the single sex amplifier.


Take the center tap and tie it to a positive voltage. Feed the other two 
inputs to the transformer with a differential signal. You have blocked 
DC from the output, restoring a ground referenced single phase. (as 
opposed to differential) output.


These active whips are prone to picking up electrical noise. Fine if you 
live in the boonies. Not so good for urban dwellers.


If the antenna is just a wire in the air, I'm not sure what good it does 
to capacitively couple the input. Who cares if some DC is floating on a 
wire just poking in the air.


While some people think of transformers are bandlimiting devices, note 
that all those coupling caps have series inductance. There is no free lunch.


Just meditating out loud, if you were to go push pull with a ferrite 
antenna AND you are winding it yourself, you could avoid the biasing 
resistors by putting a center tap in the antenna itself, then tie that 
center tap to an appropriate bias voltage. I haven't seen this done, so 
their may be a gotcha with that scheme, but the science is good. 
Generally you will get a lower noise circuit if the input device is an 
amplifier rather than a buffer.


Lanksford's input stage is essentially a push pull buffer, but I don't 
see that cancelling 2nd harmonics like a push pull amp. But for a whip, 
which is a single ended input, I don't see a way to get a differential 
input. Not true for a ferrite antenna.



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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

On Sun, 18 Mar 2012 13:25:54 +
"Poul-Henning Kamp"  wrote:

> In message <4f65d971.8070...@arcor.de>, ehydra writes:
> 
> >http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf
> > > In my implementation, it covered DC to 200MHz until I low-pass'ed it.
> >
> >His designs are always a good source but this one is AC-coupled ;-)
> 
> Not in my implementation, I have eliminated the input capacitor because
> the active element is 3cm from the PCB,

Could you explain how the distance of the antenna to the PCB is related
to a DC block capacitor? And how do you block current flowing from the
input stage of your amplifier into the antenna?

> and I drive the output with a centertapped transformer.

Do you really mean a transformer? Or just a center tapped inductor?
And how does that fit into the biasing? Or does your circuit contain
more elements at the output than a transfomer/inductor and the biasing
resistor?

Attila Kinali

-- 
Why does it take years to find the answers to
the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[ehydra]

I wonder because ALL of the shown circuits in his pdf are AC-coupled.
It is maybe possible to servo-loop with OpAmps but surely not worth the 
effort.


Useful too as a Scope FET-probe.


- Henry


Poul-Henning Kamp schrieb:
> In message <4f65d971.8070...@arcor.de>, ehydra writes:
>
>> 
http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf

>>> In my implementation, it covered DC to 200MHz until I low-pass'ed it.
>> His designs are always a good source but this one is AC-coupled ;-)
>
> Not in my implementation, I have eliminated the input capacitor because
> the active element is 3cm from the PCB, and I drive the output with
> a centertapped transformer.
>
>

--
ehydra.dyndns.info


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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <4f65d971.8070...@arcor.de>, ehydra writes:

>http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf
> > In my implementation, it covered DC to 200MHz until I low-pass'ed it.
>
>His designs are always a good source but this one is AC-coupled ;-)

Not in my implementation, I have eliminated the input capacitor because
the active element is 3cm from the PCB, and I drive the output with
a centertapped transformer.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[ehydra]

Poul-Henning Kamp schrieb:
> In message <4f64f279.4040...@arcor.de>, ehydra writes:
>> Marek Peca schrieb:
>
>>> This was almost the only reason for ferrite rod -- simplicity and
>>> attenuation of TVs, some LCDs, 50Hz etc.
>> If you make the antenna about 10x bigger you can omit the whole 
ferrite.

>
> I have used two antennas, an unloade air-coil, actually plastic-lid-coil:
>
>http://phk.freebsd.dk/loran-c/Antenna/

Yeah. I remember the red.

The degaussing coil of old TVs can work. Some resonate at 50KHz which is 
a little low but it depends on the manufacturer. So try it.



>
> and a vertical monopole based on a Chris Trask design I can highly
> recommend:
>
> 
http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf

>
> In my implementation, it covered DC to 200MHz until I low-pass'ed it.
>

His designs are always a good source but this one is AC-coupled ;-)

A CD4069 is all one needs for first experiments. I was satisfied.


- Henry

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <4f64f279.4040...@arcor.de>, ehydra writes:
>Marek Peca schrieb:

>> This was almost the only reason for ferrite rod -- simplicity and 
>> attenuation of TVs, some LCDs, 50Hz etc.
>
>If you make the antenna about 10x bigger you can omit the whole ferrite. 

I have used two antennas, an unloade air-coil, actually plastic-lid-coil:

http://phk.freebsd.dk/loran-c/Antenna/

and a vertical monopole based on a Chris Trask design I can highly
recommend:


http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf

In my implementation, it covered DC to 200MHz until I low-pass'ed it.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[ehydra]

No, there is a geometric saturation. You can't use the better
permeability in reality.

The optimum length to width relation is about 6 to 10 for ferrite rods.
Here is a diagram:
http://ehydra.dyndns.info/NG/time-nuts/Pettengill%20002.jpg


This is one of the classics in my link list:
http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html


- Henry


li...@lazygranch.com schrieb:

Wouldn't the difference be directly proportional to the relative
permeability? If so, the difference would be more like 125, not 10,
depending on core material.


--
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Brooke Clarke]

Hi:

The material permeability gets reduced to effective permeability depending on the rod length / diameter radio (you would 
like it to be >= 100) to realize the material permeability).

For example:  http://www.magneticsgroup.com/pdf/erods.pdf

More on ferrite loop sticks at:
http://www.prc68.com/I/Loop.shtml

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/Brooke4Congress.html


li...@lazygranch.com wrote:

Wouldn't the difference be directly proportional to the relative permeability? 
If so, the difference would be more like 125, not 10, depending on core 
material.

-Original Message-
From: ehydra
Sender: time-nuts-boun...@febo.com
Date: Sat, 17 Mar 2012 21:22:17
To: Marek Peca; Discussion of precise time and frequency 
measurement
Reply-To: ehy...@arcor.de, Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

Marek Peca schrieb:

This was almost the only reason for ferrite rod -- simplicity and
attenuation of TVs, some LCDs, 50Hz etc.

If you make the antenna about 10x bigger you can omit the whole ferrite.
The only benefit of a ferrite loaded coil is the size of it!
In ancient time radios had flat air coils like spider webs. In fact they
are named after spiders in german.
This air coil can be resonated too!

I can imagine a resonated vertical antenna. Never seen that but all it
requires is a low impedance pre-amp stage and a loading coil of very high Q.

- Henry



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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[ehydra]

In the end every antenna receives the EM wave! The EM-wave is the far
field. The antenna works in the near field where a dominant component
can be the E or M. That depends on the antenna. Between the near and the
far field the field is "converted" and local Z0 highly complicated.

As far as I know every antenna declared as whole EM-capable wasn't it
and I think it is maybe just impossible to couple directly EM to a
antenna .


The ferrite antenna couples the M component. The vertical capacitive
antenna the E component!
Both can be resonant or broadband.

The ferrite antenna is highly nonlinear and therefor not suitable as
transmitter. As we don't have a "reverse" component for FETs this is
even true for the vertical capacitive antenna.

And a wire antenna in the classical way is a M component antenna. No
ferrites and low Z0 means it can be effectivly used as a transmitting
device.

- Henry


li...@lazygranch.com schrieb:
The ferrite loop antenna receives the magnetic portion of the EM wave. It doesn't have to be a bandpass LC filter. 

The Wellbrook loop antennas are one example of a broadband antenna that receives the magnetic portion. 



--
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[lists]

Wouldn't the difference be directly proportional to the relative permeability? 
If so, the difference would be more like 125, not 10, depending on core 
material. 
 
-Original Message-
From: ehydra 
Sender: time-nuts-boun...@febo.com
Date: Sat, 17 Mar 2012 21:22:17 
To: Marek Peca; Discussion of precise time and frequency 
measurement
Reply-To: ehy...@arcor.de, Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

Marek Peca schrieb:
> This was almost the only reason for ferrite rod -- simplicity and 
> attenuation of TVs, some LCDs, 50Hz etc.

If you make the antenna about 10x bigger you can omit the whole ferrite. 
The only benefit of a ferrite loaded coil is the size of it!
In ancient time radios had flat air coils like spider webs. In fact they 
are named after spiders in german.
This air coil can be resonated too!

I can imagine a resonated vertical antenna. Never seen that but all it 
requires is a low impedance pre-amp stage and a loading coil of very high Q.

- Henry

-- 
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[lists]

Check out "Observations on Ferrite Rod Antennas", QEX, 2008. Type 61 works 
better at low frequencies regardless of manufacturers guidelines. 

-Original Message-
From: "Charles P. Steinmetz" 
Sender: time-nuts-boun...@febo.com
Date: Sat, 17 Mar 2012 12:01:36 
To: Discussion of precise time and frequency measurement
Reply-To: Discussion of precise time and frequency measurement
    
Subject: Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

gary wrote:

>OK, assuming type 61, it is 0.1%/deg C.

IME, Type 78 is the usual choice for resonant antennas below 200 kHz 
(tempco of initial permeability = 1.0%/deg C).  I have seen Type 33 
used for broadband LF/MF antennas (tempco of initial permeability = 
0.1%/deg C).  Type 61 is generally not used below 200 kHz.

Best regards,

Charles







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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[ehydra]

Marek Peca schrieb:
This was almost the only reason for ferrite rod -- simplicity and 
attenuation of TVs, some LCDs, 50Hz etc.


If you make the antenna about 10x bigger you can omit the whole ferrite. 
The only benefit of a ferrite loaded coil is the size of it!
In ancient time radios had flat air coils like spider webs. In fact they 
are named after spiders in german.

This air coil can be resonated too!

I can imagine a resonated vertical antenna. Never seen that but all it 
requires is a low impedance pre-amp stage and a loading coil of very high Q.


- Henry

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Charles P. Steinmetz]

gary wrote:


OK, assuming type 61, it is 0.1%/deg C.


IME, Type 78 is the usual choice for resonant antennas below 200 kHz 
(tempco of initial permeability = 1.0%/deg C).  I have seen Type 33 
used for broadband LF/MF antennas (tempco of initial permeability = 
0.1%/deg C).  Type 61 is generally not used below 200 kHz.


Best regards,

Charles







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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[lists]

The ferrite loop antenna receives the magnetic portion of the EM wave. It 
doesn't have to be a bandpass LC filter. 

The Wellbrook loop antennas are one example of a broadband antenna that 
receives the magnetic portion. 
 
-Original Message-
From: ehydra 
Sender: time-nuts-boun...@febo.com
Date: Sat, 17 Mar 2012 16:10:48 
To: Discussion of precise time and frequency measurement
Reply-To: ehy...@arcor.de, Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

Hi Marek -

I don't know where you are in CZ. I'm on the boarder in DE near PL and 
CZ. The distance to DCF77 is about 450km and if I check the amplitude 
across 24h I see considerable very deep fading effects! I think it is 
useless as a phase-coupled time receiver. At least in specific 
positions. It will loose phase at least for twice the day for approx. 2h 
! That was the report for a ferrite rod.

The other way would be a high-impedance FET-preamp vertical-wire 
antenna. I think this will resist much more fading effects. But it is 
unchecked at the moment. You're welcome to do it.

The benefit of a resonated ferrite rod is the good bandpass filtering 
for local interferers like TV. The FET vertical wire will need heavily 
filtering thereafter. All in the whole dynamice range, of course.


Ferrites can be temperature controlled. They have big spreads in 
parameters anyway! The production procedure is explained in the 
classical book about Ferrites: Snelling "Soft Ferrites".


- Henry


Marek Peca schrieb:
>> That would be 36ns group delay variation if I did the math correctly.
> 
> OK
> 
> And in article P. Hetzel: Time dissemination via the LF transmitter 
> DCF77 using a pseudo-random phase-shift keying of the carrier, 2nd EFTF 
> Neuchatel, 1988., they conclude with timing results of about 2..10e-6 s 
> RMS over ~1000km distance.
> 
> However, I do not know what is the reality and whether such a 
> performance is limited by atmosphere/ground conditions, or whether it 
> could be better within LF band.
> 
>> However, what material are you using for the ferrite? The material can 
>> have a significant tempco.
> 
> In my project, I have used noname rod taken from within DCF77 alarm clock.
> If I will recreate it, I will look for something defined at the store.
> 

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

Dear Henry,


I don't know where you are in CZ. I'm on the boarder in DE near PL and CZ.


my former measurement (the one at YouTube, fairly good reception, winter) 
has been done under Erzgebirge, Teplice, CZ. Now I moved near Sumava 
(Boehmischer Wald), so tests may follow, if I will return to the topic.


The distance to DCF77 is about 450km and if I check the amplitude across 24h 
I see considerable very deep fading effects! I think it is useless as a 
phase-coupled time receiver. At least in specific positions. It will loose 
phase at least for twice the day for approx. 2h ! That was the report for a 
ferrite rod.


Thank you.

The other way would be a high-impedance FET-preamp vertical-wire antenna. I 
think this will resist much more fading effects. But it is unchecked at the 
moment. You're welcome to do it.


The benefit of a resonated ferrite rod is the good bandpass filtering for 
local interferers like TV. The FET vertical wire will need heavily filtering 
thereafter. All in the whole dynamice range, of course.


This was almost the only reason for ferrite rod -- simplicity and 
attenuation of TVs, some LCDs, 50Hz etc.


Ferrites can be temperature controlled. They have big spreads in parameters 
anyway! The production procedure is explained in the classical book about 
Ferrites: Snelling "Soft Ferrites".


Thank you for your pointer.

Your idea of ferrite ovenization is cool.


Best regards,
Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[ehydra]

Hi Marek -

I don't know where you are in CZ. I'm on the boarder in DE near PL and 
CZ. The distance to DCF77 is about 450km and if I check the amplitude 
across 24h I see considerable very deep fading effects! I think it is 
useless as a phase-coupled time receiver. At least in specific 
positions. It will loose phase at least for twice the day for approx. 2h 
! That was the report for a ferrite rod.


The other way would be a high-impedance FET-preamp vertical-wire 
antenna. I think this will resist much more fading effects. But it is 
unchecked at the moment. You're welcome to do it.


The benefit of a resonated ferrite rod is the good bandpass filtering 
for local interferers like TV. The FET vertical wire will need heavily 
filtering thereafter. All in the whole dynamice range, of course.



Ferrites can be temperature controlled. They have big spreads in 
parameters anyway! The production procedure is explained in the 
classical book about Ferrites: Snelling "Soft Ferrites".



- Henry


Marek Peca schrieb:

That would be 36ns group delay variation if I did the math correctly.


OK

And in article P. Hetzel: Time dissemination via the LF transmitter 
DCF77 using a pseudo-random phase-shift keying of the carrier, 2nd EFTF 
Neuchatel, 1988., they conclude with timing results of about 2..10e-6 s 
RMS over ~1000km distance.


However, I do not know what is the reality and whether such a 
performance is limited by atmosphere/ground conditions, or whether it 
could be better within LF band.


However, what material are you using for the ferrite? The material can 
have a significant tempco.


In my project, I have used noname rod taken from within DCF77 alarm clock.
If I will recreate it, I will look for something defined at the store.



--
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

http://www.fair-rite.com/newfair/materials61.htm


OK, assuming type 61, it is 0.1%/deg C. Let's go with +/- 5 degrees, 
which would be for indoor use. I don't have the equation handy for a 
damped LC. Certainly undamped would be worst case. f=1/(2*pi*sqrt(LC)).


When the dust settles, the frequency shift is the square root of the 
temperature shift, so half a percent due to temperature ends up being a 
quarter percent frequency shift.





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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

That would be 36ns group delay variation if I did the math correctly.


OK

And in article P. Hetzel: Time dissemination via the LF transmitter DCF77 
using a pseudo-random phase-shift keying of the carrier, 2nd EFTF 
Neuchatel, 1988., they conclude with timing results of about 2..10e-6 s 
RMS over ~1000km distance.


However, I do not know what is the reality and whether such a performance 
is limited by atmosphere/ground conditions, or whether it could be better 
within LF band.


However, what material are you using for the ferrite? The material can have a 
significant tempco.


In my project, I have used noname rod taken from within DCF77 alarm clock.
If I will recreate it, I will look for something defined at the store.


Regards,
Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

That would be 36ns group delay variation if I did the math correctly.

However, what material are you using for the ferrite? The material can 
have a significant tempco.



On 3/17/2012 7:17 AM, Marek Peca wrote:


However, for f0=77.5kHz and B=1kHz, the LC circuit with Q=40 gives phase
error over specified bandwidth about +-0.5deg p-p. Does such a phase
non-linearity bother you?


Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

I think the tempco of the ferrite is more significant than drift in the 
analog filter.


Perhaps I was unclear in this as well. I do not use nor plan to use any 
other filter than the (ferrite-L)-C resonant circuit itself. So, yes, the 
tempco of the ferrite makes its coefficients variation.


The question is, whether phase errors <1deg p-p over 1kHz band are 
significant.


Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

I think the tempco of the ferrite is more significant than drift in the 
analog filter. Of course this again implies the better design is to not 
load the inductor with a cap, i.e. stay broadband, and then just filter 
post the preamp.


The open circuit voltage will be lower without the resonant circuit. 
This is a case where the BF862 might do some good since the goal is to 
not load the inductor, either resistively or with capacitance. When you 
are dealing with components that are around 1nV/sqrt(hz), you can afford 
to throw some circuitry at the problem especially since the atmospheric 
noise will dominate.




On 3/17/2012 6:38 AM, Marek Peca wrote:

Any filter's group delay can be equalized by all pass filters.

Delay builds up at the filter corner. Since everything in the real
world is causal, you add delay outside that corner frequency but in
the passband to equalize it. This is to say, you can't remove delay,
but just add it to flatten out the group delay.


Yes, the compensation can be made and it has been also pointed out in
the first comment by Poul-Henning.

The only remaining question is, how stable are the analogue filter
parameters over time, to be compensated by fixed digital filter. It
seems to me, that some very small phase errors produced by such a
filter-filter mismatch may be acceptable.

At least for low-cost device which I would like to rebuild and offer for
WWVB audience (which is not present in our land).


Best regards,
Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

Yes, in order to equalize group delay, you need to know what to equalize. But 
with an educated guess as to the system response, he could get close.


All this said, in 2012, I would rather the amplifier be simple gain, the 
inductor not loaded with capacitance and the filtering done past the 
amplifier. We aren't living in the era of 3 transistor circuits.


When delta-sigma converters came on the scene. I wisely found new design 
skills. [They replaced much analog filtering.] So better just to do the 
filtering in DSP IF there is no critical power budget.


This may not be true, if you have some strong interference at the ferrite 
rod input. Of course, if it would be strong and near the signal frequency, 
it will not be attenuated much even by the 2nd order LC circuit, indeed.


However, for f0=77.5kHz and B=1kHz, the LC circuit with Q=40 gives phase 
error over specified bandwidth about +-0.5deg p-p. Does such a phase 
non-linearity bother you?



Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Bob Camp]

Hi

The problem with delay compensation in a Time Nut environment is that to do it 
you add delay. Your all pass network adds enough delay to the "fast" part of 
the passband to make it come out the same as the slow part. In real circuits 
you inevitably add some delay everywhere with the all pass, so the net is 
somewhat higher delay everywhere than the worst of the original filter. 

So far no problem.

Change temperature or let things age and all those delays change. Since they 
are a sum of many things, they likely change in a complicated fashion. Change 
in delay is change in time. That is a Time Nut problem. 

Bob



On Mar 17, 2012, at 9:40 AM, gary  wrote:

> Which basically matched my assumption. If the inductor is loaded, you have a 
> narrowband filter. So again, this does not imply that a ferrite rod antenna 
> per se has phase distortion. It is the LC filter than effects the group delay.
> 
> 
> On 3/17/2012 6:19 AM, Marek Peca wrote:
>> Hello, gary,
>> 
>>> I lost track of who wrote this, but why is it assume a ferrite rod has
>>> non-linear phase. [Group delay error I presume). Now I assume this
>>> presumes the rod is used in a LC circuit, but if the Q is not high,
>>> the phase linearity won't necessarily be bad.
>>> 
>>> Basically I'd like to hear more from whomever wrote this.
>> 
>> It was me, a time-nuts newbie. My previous related posts were:
>> http://www.febo.com/pipermail/time-nuts/2012-March/065049.html
>> http://www.febo.com/pipermail/time-nuts/2012-March/065003.html
>> http://www.febo.com/pipermail/time-nuts/2012-March/065009.html
>> etc.
>> and
>> http://www.febo.com/pipermail/time-nuts/2012-March/065135.html
>> 
>>> "The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like
>>> standards with PRBS is about 1.5kHz. Of course the ferrite rod as an
>>> input filter *will* have a non-linear phase, but it still seems to me
>>> it is the simplest and most common receiptor for LF time signals."
>> 
>> 
>> Let me clarify the unclear statement. I was reacting to Poul-Henning
>> Kamp's (true) statement, that: "The reason I use 1MSPS is that it allows
>> me to use a very sloppy low-pass filter filter which just cuts off
>> somewhere around 150-200 kHz, and do everything else in software. This
>> means that I have no phase/group-delay distortion in the analog part
>> that I need to compensate in software."
>> 
>> In my design, I have used a ferrite rod LC circuit as and antenna and
>> also the only element of selectivity in front of sampling. So, there was
>> a 2nd order only filter.
>> 
>> The useful signal of DCF77 (afaik yout WWVB is very similar now with
>> BPSK) spans over ~1kHz. In my design, in contrast to P.-H. K.'s
>> approach, I use only ~40ksps, so the 2nd order ferrite rod circuit
>> should pass 1kHz, but it should attenuate somewhere around +-10..20kHz.
>> 
>> I.e., the result will be always a compromise. Unfortunately, I don't
>> have a measurement of my worked circuit's Q, but let us assume Q=20..100
>> can be realistic value for ferrite rods. Then, the filter's BW will be
>> somewhere 0.8..4kHz, what means, that its phase over the interesting
>> 1kHz band will _not_ be straight line, but somewhat curved.
>> 
>> This is the only thing about ferrite rod and phase I meant.
>> 
>> To conclude, I would like to repeat, that in my oppinion the ferrite rod
>> is easy and common antenna for LF signals, so that in such a case the
>> phase will be curved anyway. Of course you can feed the P.-H. K.'s 1Msps
>> input by more wide-band antenna, not the ferrite rod, to get more linear
>> phase without SW compensation.
>> 
>> 
>> Greeting from Marek
>> 
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

Which basically matched my assumption. If the inductor is loaded, you have a 
narrowband filter. So again, this does not imply that a ferrite rod antenna 
per se has phase distortion. It is the LC filter than effects the group 
delay.


Yes, exactly. Excuse my loose speech before not explicitly mentioning LC 
tuned circuit.


Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

Yes, in order to equalize group delay, you need to know what to 
equalize. But with an educated guess as to the system response, he could 
get close.


All this said, in 2012, I would rather the amplifier be simple gain, the 
inductor not loaded with capacitance and the filtering done past the 
amplifier. We aren't living in the era of 3 transistor circuits.


When delta-sigma converters came on the scene. I wisely found new design 
skills. [They replaced much analog filtering.] So better just to do the 
filtering in DSP IF there is no critical power budget.



On 3/17/2012 6:25 AM, Attila Kinali wrote:

On Sat, 17 Mar 2012 06:13:28 -0700
gary  wrote:


On 3/17/2012 5:44 AM, Attila Kinali wrote:

On Sat, 17 Mar 2012 10:15:17 +
"Poul-Henning Kamp"   wrote:


Either you need to characterize the exact behaviour of your filter
and build the necessary compensation for its phase/frequency behaviour
into your receiver, or you need a very flat filter (both freq+phase)
in order to reliably recognize the proper zero-crossing to track.


BTW: how do you compensate for the filter characteristics of your
magnetic loop antenna?



Any filter's group delay can be equalized by all pass filters.

Delay builds up at the filter corner. Since everything in the real world
is causal, you add delay outside that corner frequency but in the
passband to equalize it. This is to say, you can't remove delay, but
just add it to flatten out the group delay.


Sorry, i asked in a misleading way. I didnt mean to ask what technique
to use to flaten the phase delay, but rather how does phk know how the
compensating filter should look like? For this, one needs to exactly
characterize the antenna-amplifier chain...AFAIK

Attila Kinali



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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

Which basically matched my assumption. If the inductor is loaded, you 
have a narrowband filter. So again, this does not imply that a ferrite 
rod antenna per se has phase distortion. It is the LC filter than 
effects the group delay.



On 3/17/2012 6:19 AM, Marek Peca wrote:

Hello, gary,


I lost track of who wrote this, but why is it assume a ferrite rod has
non-linear phase. [Group delay error I presume). Now I assume this
presumes the rod is used in a LC circuit, but if the Q is not high,
the phase linearity won't necessarily be bad.

Basically I'd like to hear more from whomever wrote this.


It was me, a time-nuts newbie. My previous related posts were:
http://www.febo.com/pipermail/time-nuts/2012-March/065049.html
http://www.febo.com/pipermail/time-nuts/2012-March/065003.html
http://www.febo.com/pipermail/time-nuts/2012-March/065009.html
etc.
and
http://www.febo.com/pipermail/time-nuts/2012-March/065135.html


"The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like
standards with PRBS is about 1.5kHz. Of course the ferrite rod as an
input filter *will* have a non-linear phase, but it still seems to me
it is the simplest and most common receiptor for LF time signals."



Let me clarify the unclear statement. I was reacting to Poul-Henning
Kamp's (true) statement, that: "The reason I use 1MSPS is that it allows
me to use a very sloppy low-pass filter filter which just cuts off
somewhere around 150-200 kHz, and do everything else in software. This
means that I have no phase/group-delay distortion in the analog part
that I need to compensate in software."

In my design, I have used a ferrite rod LC circuit as and antenna and
also the only element of selectivity in front of sampling. So, there was
a 2nd order only filter.

The useful signal of DCF77 (afaik yout WWVB is very similar now with
BPSK) spans over ~1kHz. In my design, in contrast to P.-H. K.'s
approach, I use only ~40ksps, so the 2nd order ferrite rod circuit
should pass 1kHz, but it should attenuate somewhere around +-10..20kHz.

I.e., the result will be always a compromise. Unfortunately, I don't
have a measurement of my worked circuit's Q, but let us assume Q=20..100
can be realistic value for ferrite rods. Then, the filter's BW will be
somewhere 0.8..4kHz, what means, that its phase over the interesting
1kHz band will _not_ be straight line, but somewhat curved.

This is the only thing about ferrite rod and phase I meant.

To conclude, I would like to repeat, that in my oppinion the ferrite rod
is easy and common antenna for LF signals, so that in such a case the
phase will be curved anyway. Of course you can feed the P.-H. K.'s 1Msps
input by more wide-band antenna, not the ferrite rod, to get more linear
phase without SW compensation.


Greeting from Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

Any filter's group delay can be equalized by all pass filters.

Delay builds up at the filter corner. Since everything in the real world is 
causal, you add delay outside that corner frequency but in the passband to 
equalize it. This is to say, you can't remove delay, but just add it to 
flatten out the group delay.


Yes, the compensation can be made and it has been also pointed out in the 
first comment by Poul-Henning.


The only remaining question is, how stable are the analogue filter 
parameters over time, to be compensated by fixed digital filter. It seems 
to me, that some very small phase errors produced by such a filter-filter 
mismatch may be acceptable.


At least for low-cost device which I would like to rebuild and offer for 
WWVB audience (which is not present in our land).



Best regards,
Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

I've designed filters for datacom chips. I know filtering. My point is 
the original author is making some assumptions in the design which are 
not stated.


Yes, my fault, I didn't write it properly, so by a "ferrite rod" in 
context of DCF/WWVB reception, I meand a "ferrite antenna in an LC tuned 
circuit".


Apologies for all who have been confused.

What I don't have a lot of hands on experience is with open circuit 
magnetics. (I do with closed circuit magnetics.) But I claim if the 
ferrite rod antenna is not capacitively loaded to resonate at the comm 
frequency, then there isn't significant group delay error.


Yes, see above. I meant an LC circuit, containing the ferrite rod antenna 
as the L.


The antenna will have a natural resonant frequency comprised of the 
inductance and parasitic capacitance. But this represents an upper 
frequency limit. So simply operate below resonance and the group delay 
error is minimized. Filtering can be done following the preamp that 
connects to the antenna, and thus will not interact with it.



Thank you for your understanding.
Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

Dear Poul-Henning,


My only argument against your versatile and well-performing solution is
that it is a little bit overkill.


As if running a handfull precision oscillators just for fun isn't
"overkill" also ? :-)


I don't know -- are there any limits for the fun in a time-nut sense? :-)
I hope not. The point is, with which kind of toy we would like to play.


In other words, it would be certainly better to buy USRP N210,


Actually that would be a very idea, because you cannot get rid of
the down-sampler in the USRP and that would make Loran-C reception
very tricky to implement.


Are you sure there are such a limitations? I must reveal, that I have not 
even once played with USRP N210, but I hope it does not have any BW 
limitations up to the Gig-Eth speed.


Anyway, it would be an expensive and heavy receiver for LF-only signals.


My point is to do something with relevant performance wrt. <10kHz wide
LF signals.


The crucial question is if your are doing timenuttery or radionuttery.

If you are doing timenuttery, you want you ADC synchronized to your
OCXO/Rb/Cs or whatever you have,


Yes, I would like to have an option of external frequency standard.
However, I would like to lock ordinary onboard quartz too, since many 
people without Rb (though they are pretty cheap these days) may use it as 
a disciplined frequency source, too. I mean no time-nuts, but ordinary 
hobbyists, going to tune their filters etc.


Or people, wanting some time signal in place of poor GNSS reception 
without good NTP access (I know such a set i almost empty :-)).


and you don't want to have to deal with getting your IF frequency locked 
too.


Soundcards use inconvenient frequencies and are seldom built to take
an external clock signal.


So this is why I would like to supply a little bit tweaked "sound card", 
tailored to receive LF-HF band signals up to say 10..20kHz of width.



The useful bandwidth of LF to HF radio is about 9kHz,


You need more than 25kHz for good Loran-C


OK, thank you for this notice. I have not yet thinked about Loran, so I 
must look in more detail on it.



Best regards,
Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

On Sat, 17 Mar 2012 06:13:28 -0700
gary  wrote:

> On 3/17/2012 5:44 AM, Attila Kinali wrote:
> > On Sat, 17 Mar 2012 10:15:17 +
> > "Poul-Henning Kamp"  wrote:
> >
> >> Either you need to characterize the exact behaviour of your filter
> >> and build the necessary compensation for its phase/frequency behaviour
> >> into your receiver, or you need a very flat filter (both freq+phase)
> >> in order to reliably recognize the proper zero-crossing to track.
> >
> > BTW: how do you compensate for the filter characteristics of your
> > magnetic loop antenna?

> Any filter's group delay can be equalized by all pass filters.
> 
> Delay builds up at the filter corner. Since everything in the real world 
> is causal, you add delay outside that corner frequency but in the 
> passband to equalize it. This is to say, you can't remove delay, but 
> just add it to flatten out the group delay.

Sorry, i asked in a misleading way. I didnt mean to ask what technique
to use to flaten the phase delay, but rather how does phk know how the
compensating filter should look like? For this, one needs to exactly
characterize the antenna-amplifier chain...AFAIK

Attila Kinali

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

Hello, gary,

I lost track of who wrote this, but why is it assume a ferrite rod has 
non-linear phase. [Group delay error I presume). Now I assume this presumes 
the rod is used in a LC circuit, but if the Q is not high, the phase 
linearity won't necessarily be bad.


Basically I'd like to hear more from whomever wrote this.


It was me, a time-nuts newbie. My previous related posts were:
http://www.febo.com/pipermail/time-nuts/2012-March/065049.html
http://www.febo.com/pipermail/time-nuts/2012-March/065003.html
http://www.febo.com/pipermail/time-nuts/2012-March/065009.html
etc.
and
http://www.febo.com/pipermail/time-nuts/2012-March/065135.html

"The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like standards 
with PRBS is about 1.5kHz. Of course the ferrite rod as an input filter 
*will* have a non-linear phase, but it still seems to me it is the simplest 
and most common receiptor for LF time signals."



Let me clarify the unclear statement. I was reacting to Poul-Henning 
Kamp's (true) statement, that: "The reason I use 1MSPS is that it allows 
me to use a very sloppy low-pass filter filter which just cuts off 
somewhere around 150-200 kHz, and do everything else in software. This 
means that I have no phase/group-delay distortion in the analog part that 
I need to compensate in software."


In my design, I have used a ferrite rod LC circuit as and antenna and also 
the only element of selectivity in front of sampling. So, there was a 2nd 
order only filter.


The useful signal of DCF77 (afaik yout WWVB is very similar now with BPSK) 
spans over ~1kHz. In my design, in contrast to P.-H. K.'s approach, I use 
only ~40ksps, so the 2nd order ferrite rod circuit should pass 1kHz, but 
it should attenuate somewhere around +-10..20kHz.


I.e., the result will be always a compromise. Unfortunately, I don't have 
a measurement of my worked circuit's Q, but let us assume Q=20..100 can be 
realistic value for ferrite rods. Then, the filter's BW will be somewhere 
0.8..4kHz, what means, that its phase over the interesting 1kHz band will 
_not_ be straight line, but somewhat curved.


This is the only thing about ferrite rod and phase I meant.

To conclude, I would like to repeat, that in my oppinion the ferrite rod 
is easy and common antenna for LF signals, so that in such a case the 
phase will be curved anyway. Of course you can feed the P.-H. K.'s 1Msps 
input by more wide-band antenna, not the ferrite rod, to get more linear 
phase without SW compensation.



Greeting from Marek

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

Any filter's group delay can be equalized by all pass filters.

Delay builds up at the filter corner. Since everything in the real world 
is causal, you add delay outside that corner frequency but in the 
passband to equalize it. This is to say, you can't remove delay, but 
just add it to flatten out the group delay.





On 3/17/2012 5:44 AM, Attila Kinali wrote:

On Sat, 17 Mar 2012 10:15:17 +
"Poul-Henning Kamp"  wrote:


Either you need to characterize the exact behaviour of your filter
and build the necessary compensation for its phase/frequency behaviour
into your receiver, or you need a very flat filter (both freq+phase)
in order to reliably recognize the proper zero-crossing to track.


BTW: how do you compensate for the filter characteristics of your
magnetic loop antenna?

Attila Kinali


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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

On Sat, 17 Mar 2012 10:15:17 +
"Poul-Henning Kamp"  wrote:

> Either you need to characterize the exact behaviour of your filter
> and build the necessary compensation for its phase/frequency behaviour
> into your receiver, or you need a very flat filter (both freq+phase)
> in order to reliably recognize the proper zero-crossing to track.

BTW: how do you compensate for the filter characteristics of your
magnetic loop antenna?

Attila Kinali
-- 
Why does it take years to find the answers to
the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

On Sat, 17 Mar 2012 10:27:03 +
li...@lazygranch.com wrote:

> What I don't have a lot of hands on experience is with open circuit
> magnetics. (I do with closed circuit magnetics.) But I claim if the
> ferrite rod antenna is not capacitively loaded to resonate at the
> comm frequency, then there isn't significant group delay error. 

Ah.. you have here  a "wrong" assumption. Normal antennas are resonant
at the wanted frequency. This is in order to get maximum gain i the
first stage (not to mention that the antenna is the only "amplifier"
with no noise). Also all DCF77 antennas i have seen so far are ferrit
rods with an attached capacitor, to form a resonant antenna.

I think, it would be possible to use a non-resonant antenna. I don't
know what the total noise would then be. But it would definitly be
interesting to know whether a non-resonant antenna design would be
better or worse.

Attila Kinali

-- 
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the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

On Sat, 17 Mar 2012 10:15:17 +
"Poul-Henning Kamp"  wrote:

> In message <2012031719.9536107ebf82050fe14ee...@kinali.ch>, Attila Kinali 
> w
> rites:
> >On Sat, 17 Mar 2012 10:01:13 +
> 
> >Could you explain why? Yes, you need a higher BW for Loran-C,
> >but the phase(f) function will give you only a distortion of
> >the signal and a constant time delay in your signal recovery.
> >But that shouldnt degrade the usefullness of the system.
> >What am i missing here?
> 
> Either you need to characterize the exact behaviour of your filter
> and build the necessary compensation for its phase/frequency behaviour
> into your receiver, or you need a very flat filter (both freq+phase)
> in order to reliably recognize the proper zero-crossing to track.
> 
> The more you disturb a Loran-C pulse, the more it just looks like
> a bit of a sine-function, and the harder it is to lock on the right
> zero-crossing.

Ah.. so it is because Loran-C uses the third zero crossing as specified
measurement point, which you thus have to capture with the greates
possible resolution.

Am i right that for DCF77, WWVB and the like, where there is no such
requirement on the zero crossing of a pulse, one can just lock to the
carrier and the distortions from filters are not so relevant?

Attila Kinali
-- 
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the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[lists]

I've designed filters for datacom chips. I know filtering. My point is the 
original author is making some assumptions in the design which are not stated.  

What I don't have a lot of hands on experience is with open circuit magnetics. 
(I do with closed circuit magnetics.) But I claim if the ferrite rod antenna is 
not capacitively loaded to resonate at the comm frequency, then there isn't 
significant group delay error. 

The antenna will have a natural resonant frequency comprised of the inductance 
and parasitic capacitance. But this represents an upper frequency limit. So 
simply operate below resonance and the group delay error is minimized. 
Filtering can be done following the preamp that connects to the antenna, and 
thus will not interact with it.

 

-Original Message-
From: Attila Kinali 
Sender: time-nuts-boun...@febo.com
Date: Sat, 17 Mar 2012 10:47:23 
To: Discussion of precise time and frequency measurement
Reply-To: Discussion of precise time and frequency measurement
        
Subject: Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

On Fri, 16 Mar 2012 20:02:27 -0700
gary  wrote:

> I lost track of who wrote this, but why is it assume a ferrite rod has 
> non-linear phase. [Group delay error I presume). Now I assume this 
> presumes the rod is used in a LC circuit, but if the Q is not high, the 
> phase linearity won't necessarily be bad.
> 
> Basically I'd like to hear more from whomever wrote this.
> 
> 
> "The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like 
> standards with PRBS is about 1.5kHz. Of course the ferrite rod as an 
> input filter *will* have a non-linear phase, but it still seems to me it 
> is the simplest and most common receiptor for LF time signals."

I'm not the one who wrote this, but it is true :-)
Any filter has its phase dependend on the frequency. As a rule
of thumb: the higher order the filter, the faster the phase changes.

As long as you just do straight filtering, with no feed back, you
care seldom about the phase. It's the amplitude of the signal you
are interested in. But if you now go time nuttery, phase change means
delay. And you dont know how large it exactly is, because you dont
know where exactly the resonance frequency of the filter is. And more
importantly, you cannot say how it changes over time (tempeture dependece,
aging, etc).

That said, i think this can be ignored for all practical purposes
in an VLF receiver, as the enviromental changes in the atmospheric
signal path are much larger than the small error you get from the
filter. But then again, time nuts are time nuts ;)

Attila Kinali

-- 
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the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <2012031719.9536107ebf82050fe14ee...@kinali.ch>, Attila Kinali w
rites:
>On Sat, 17 Mar 2012 10:01:13 +

>Could you explain why? Yes, you need a higher BW for Loran-C,
>but the phase(f) function will give you only a distortion of
>the signal and a constant time delay in your signal recovery.
>But that shouldnt degrade the usefullness of the system.
>What am i missing here?

Either you need to characterize the exact behaviour of your filter
and build the necessary compensation for its phase/frequency behaviour
into your receiver, or you need a very flat filter (both freq+phase)
in order to reliably recognize the proper zero-crossing to track.

The more you disturb a Loran-C pulse, the more it just looks like
a bit of a sine-function, and the harder it is to lock on the right
zero-crossing.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

On Sat, 17 Mar 2012 10:01:13 +
"Poul-Henning Kamp"  wrote:

> >That said, i think this can be ignored for all practical purposes
> >in an VLF receiver, as the enviromental changes in the atmospheric
> >signal path are much larger than the small error you get from the
> >filter. But then again, time nuts are time nuts ;)
> 
> Again: it most certainly can not be ignored for Loran-C

Could you explain why? Yes, you need a higher BW for Loran-C,
but the phase(f) function will give you only a distortion of
the signal and a constant time delay in your signal recovery.
But that shouldnt degrade the usefullness of the system.
What am i missing here?

Attila Kinali

-- 
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the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <20120317104723.8c1832454f14a3f91a4fb...@kinali.ch>, Attila Kinali w
rites:

>That said, i think this can be ignored for all practical purposes
>in an VLF receiver, as the enviromental changes in the atmospheric
>signal path are much larger than the small error you get from the
>filter. But then again, time nuts are time nuts ;)

Again: it most certainly can not be ignored for Loran-C

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

On Fri, 16 Mar 2012 20:02:27 -0700
gary  wrote:

> I lost track of who wrote this, but why is it assume a ferrite rod has 
> non-linear phase. [Group delay error I presume). Now I assume this 
> presumes the rod is used in a LC circuit, but if the Q is not high, the 
> phase linearity won't necessarily be bad.
> 
> Basically I'd like to hear more from whomever wrote this.
> 
> 
> "The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like 
> standards with PRBS is about 1.5kHz. Of course the ferrite rod as an 
> input filter *will* have a non-linear phase, but it still seems to me it 
> is the simplest and most common receiptor for LF time signals."

I'm not the one who wrote this, but it is true :-)
Any filter has its phase dependend on the frequency. As a rule
of thumb: the higher order the filter, the faster the phase changes.

As long as you just do straight filtering, with no feed back, you
care seldom about the phase. It's the amplitude of the signal you
are interested in. But if you now go time nuttery, phase change means
delay. And you dont know how large it exactly is, because you dont
know where exactly the resonance frequency of the filter is. And more
importantly, you cannot say how it changes over time (tempeture dependece,
aging, etc).

That said, i think this can be ignored for all practical purposes
in an VLF receiver, as the enviromental changes in the atmospheric
signal path are much larger than the small error you get from the
filter. But then again, time nuts are time nuts ;)

Attila Kinali

-- 
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the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

Moin!

On Fri, 16 Mar 2012 13:45:04 +
"Poul-Henning Kamp"  wrote:

> >Hmm.. i someday have to look for a good introdcution into this stuff
> >that doesn't rely on a lot of math. All the books i have rely at least
> >on Laplace.. often on z-transformation as well. And that math isn't 
> >high school level anymore.
> 
> This one isn't half bad: http://www.dspguide.com/

Juup, that one looks nice.

Thanks!

Attila Kinali

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message , Marek Peca writes:

>My only argument against your versatile and well-performing solution is 
>that it is a little bit overkill.

As if running a handfull precision oscillators just for fun isn't
"overkill" also ? :-)

>In other words, it would be certainly better to buy USRP N210,

Actually that would be a very idea, because you cannot get rid of
the down-sampler in the USRP and that would make Loran-C reception
very tricky to implement.

>My point is to do something with relevant performance wrt. <10kHz wide 
>LF signals.

The crucial question is if your are doing timenuttery or radionuttery.

If you are doing timenuttery, you want you ADC synchronized to your
OCXO/Rb/Cs or whatever you have, and you don't want to have to deal
with getting your IF frequency locked too.

Soundcards use inconvenient frequencies and are seldom built to take
an external clock signal.

>The useful bandwidth of LF to HF radio is about 9kHz, 

You need more than 25kHz for good Loran-C

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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Re: [time-nuts] WWVB BPSK Receiver Project?

[michael batchelor]

So, I just recently started trying to resurrect a Spectracom 8160A reference 
oscillator. I'm assuming this is proposed WWVB change going to bite me in the 
butt on this project as well. Not sure how it differs from units like the HP 
117, but my understanding is that most of the old VLF receivers work about the 
same. 


Do I understand this correctly?  I'm kind of new to all this. Jeez, what a time 
to get back in a hobby. 


Michael - KA7ZNZ
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[gary]

I lost track of who wrote this, but why is it assume a ferrite rod has 
non-linear phase. [Group delay error I presume). Now I assume this 
presumes the rod is used in a LC circuit, but if the Q is not high, the 
phase linearity won't necessarily be bad.


Basically I'd like to hear more from whomever wrote this.


"The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like 
standards with PRBS is about 1.5kHz. Of course the ferrite rod as an 
input filter *will* have a non-linear phase, but it still seems to me it 
is the simplest and most common receiptor for LF time signals."


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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

Hello,

thank you for your oppinion.


On Thu, 15 Mar 2012, Poul-Henning Kamp wrote:


In message , Marek Peca writes:

Yes, it should work on any USB audio capable OS, ie. Linux, Windows, 
MacOS etc.


I would like to recommend against this approach for a number of reasons.

First, yes, while you can do undersampling and such, it puts very high 
requirements on your analog filters.


The reason I use 1MSPS is that it allows me to use a very sloppy 
low-pass filter filter which just cuts off somewhere around 150-200 kHz, 
and do everything else in software.


This means that I have no phase/group-delay distortion in the analog 
part that I need to compensate in software.


It also means that I don't have to change hardware to play with different
signals, they're all there, all the time, for instance the stuff under
http://phk.freebsd.dk/Leap/
is pulled out that way.
(..)



You are right. I admit, that using comfortable oversampling, the converter 
is more versatile and analogue-side filters are absolutely non-critical 
ones. Nothing against that, moreover, I confess that I often use this 
approach, oversampling & simple anti-aliasing, rather than converse.



Now, I am still unsure whether to deploy the relatively cheap lower 
performance board with sampling in order of 40..80ksps.


You are right, that 1Msps solves the task better or at least with the same 
performance. But, you pay few $ more (not so important), some few watts 
more and take more data before decimation (may be done in FPGA, of 
course). I know that USB2.0 handles >30MB/s on majority of HW&OSes and you 
still need only about 2MB/s.


My only argument against your versatile and well-performing solution is 
that it is a little bit overkill. In other words, it would be certainly 
better to buy USRP N210, then you may sample directly 0..250MHz @>100Msps, 
and 1Gbps Ethernet is quite common these days, too. You have everything 
coded inside and its software support is also very good, including virtual 
soundcard connection etc.


My point is to do something with relevant performance wrt. <10kHz wide 
LF signals.


Well, I still think that 40..100ksps (1-2 inputs) module acting like a 
SAR sound-card may be usable as well as 1Msps for LF time-nuttery with a 
bare ferrite rod, and together with a mixer for DRM and Synchronous AM 
fans.


The useful bandwidth of LF to HF radio is about 9kHz, DCF77-like standards 
with PRBS is about 1.5kHz. Of course the ferrite rod as an input filter 
*will* have a non-linear phase, but it still seems to me it is the 
simplest and most common receiptor for LF time signals.



Well, I will wait for more reactions, till now I have 2 positive and
1 yours, discouraging from 40ksps approach.


Thank you and please note my respect to your approach and achievements.


Best regards,
Marek

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Dennis Ferguson]

On 14 Mar, 2012, at 18:08 , Brooke Clarke wrote:
> The WWB paper "New Improved System for WWVB Broadcast" given at the 43rd PTTI 
> November 2011 is at:  http://jks.com/wwvb.pdf
> 
> Part of the processing gain comes directly from the BPSK modulation and that 
> amounts to a little over 10 dB improvement, but there's a further 18 dB gain 
> to be had by accumulating an hours worth of data and processing that.

It is a little interesting that the PTTI paper left out some
of the interesting details one would need to actually decode
the new signal, in particular the specification of the 14
second "Sync" sequence, which is necessary to know to find
the alignment of minutes, and the value of the "60-bit
hour-synchronization code", which defines the sequence
of phase reversals in each minute's modulation in an
hour and, as I understand it, is necessary to know to
take full advantage of the hour-averaging thing.

I assume this might have been done to allow the company
which participated in the design of the signal to complete
a receiver for it before they start transmitting that
way while keeping anyone else from starting a receiver
project until after the transmissions start?

Dennis Ferguson
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Bob Camp]

Hi

With a reasonable sized data set, I suspect we would learn some things about
the phase shift process. The better we can model the process, the better we
can anticipate it and correct for it in the code.

Bob

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Tom Van Baak
Sent: Friday, March 16, 2012 12:59 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

Bob,

To address that diurnal phase issue, for fun, we could set up a
cloud-based time-nuts WWVB common view network. With a
couple of sites in each state, imagine the wonderful daily or
hourly animated plots that would result.

/tvb

> Hi
> 
> My main concern on short averages is the relatively long path from WWVB to
> most of the target audience. The day / night phase shift is fairly
> significant over a long path. That's something I would want to process
out.
> Since it (hopefully) is predictable, it's just another thing to feed into
> the signal estimation side of the process. 
> 
> Bob



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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Tom Van Baak]

Bob,

To address that diurnal phase issue, for fun, we could set up a
cloud-based time-nuts WWVB common view network. With a
couple of sites in each state, imagine the wonderful daily or
hourly animated plots that would result.

/tvb


Hi

My main concern on short averages is the relatively long path from WWVB to
most of the target audience. The day / night phase shift is fairly
significant over a long path. That's something I would want to process out.
Since it (hopefully) is predictable, it's just another thing to feed into
the signal estimation side of the process. 


Bob




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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message , "Bob Camp" writes:

>My main concern on short averages is the relatively long path from WWVB to
>most of the target audience. The day / night phase shift is fairly
>significant over a long path.

So do I relative to DCF77 which I used for my experiments.

The point about having 8 buffers per day is that you only compare
03:00-05:59 to 03:00-05:59 the previous or the next day, so the
sun-effects almost entirely cancel out.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Bob Camp]

Hi

My main concern on short averages is the relatively long path from WWVB to
most of the target audience. The day / night phase shift is fairly
significant over a long path. That's something I would want to process out.
Since it (hopefully) is predictable, it's just another thing to feed into
the signal estimation side of the process. 

Bob

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Friday, March 16, 2012 12:27 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

In message <34c510bb3c6449b89ac4f7fbc20f4...@vectron.com>, "Bob Camp"
writes:

>One assumption is that you will indeed be capturing / averaging for several
>days. I'd include some sort of model for sunrise / sunset shifts (might be
>just "ignore for the next hour"). 

Some of my best results had 8 buffers each used for 3 hours and
all timenuttery based on 24 hour differences from these buffers.

>Another assumption is that your local reference is close enough and stable
>enough to make a multi day average meaningful. 

Well, the above technique got me a new offset estimate every three hours
and that did a pretty good job on both OCXO and Rb disciplining.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <34c510bb3c6449b89ac4f7fbc20f4...@vectron.com>, "Bob Camp" writes:

>One assumption is that you will indeed be capturing / averaging for several
>days. I'd include some sort of model for sunrise / sunset shifts (might be
>just "ignore for the next hour"). 

Some of my best results had 8 buffers each used for 3 hours and
all timenuttery based on 24 hour differences from these buffers.

>Another assumption is that your local reference is close enough and stable
>enough to make a multi day average meaningful. 

Well, the above technique got me a new offset estimate every three hours
and that did a pretty good job on both OCXO and Rb disciplining.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Bob Camp]

Hi

One assumption is that you will indeed be capturing / averaging for several
days. I'd include some sort of model for sunrise / sunset shifts (might be
just "ignore for the next hour"). 
Another assumption is that your local reference is close enough and stable
enough to make a multi day average meaningful. 

Bob

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Friday, March 16, 2012 9:03 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

In message , "Bob Camp"
writes:

>Could you generate a "lead" and a "lag" estimate of the signal (in addition
>to your "center") and integrate against each of them on the fly? If so you
>would need a *lot* less memory. I seem to recall you tried something like
>this on the one of the Loran receivers. 

The reason to use the lead/center/lag model, is that you have a moving
signal you need to track, but for timenuts purposes the signal is not
going to move more than a few microseconds over an hour, so it is
probably a better strategy to just average the heck out of the signal.

It is not even clear to me that the phase-coding helps frequency
reception at all, I tried it with the very strong phase-coding of
DCF77 and there was no statistical significance relative to heavy
duty carrier averaging.

But it clearly helps a lot with phase-determination, and for that
lead/center/lag is the way to go, but you may still want to average
for a minute, then resolve the phase using the phase-modulation,
rather than run it in real-time.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <20120316141539.d8305feaa33c99781667e...@kinali.ch>, Attila Kinali w
rites:

>Hmm.. i someday have to look for a good introdcution into this stuff
>that doesn't rely on a lot of math. All the books i have rely at least
>on Laplace.. often on z-transformation as well. And that math isn't 
>high school level anymore.

This one isn't half bad: http://www.dspguide.com/


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

On Fri, 16 Mar 2012 03:08:47 -0700
Hal Murray  wrote:

> 
> p...@phk.freebsd.dk said:
> >> Hmm... do you mean you want to store all samples of an hour and then
> >> avarage over it?
> 
> > That would be the ideal way to do it, since it would make one heck of a comb
> > filter and eliminate pretty much anything else. 
> 
> That only works if your reference clock is stable enough over the collecting 
> period.

Not necessarily. The noise of the VLF signal is much higher than the
noise of your crystal, hence the limit will not be the stability of
your crystal. Beside, integrating over such long periods tend to eliminate
noise sources. 

> I'm far from a DSP wizard.  Assume I have a signal at 100 kHz with a 
> bandwidth of 1 kHz.  (or pick any numbers you like)  How many samples per 
> second do I need?  How stable does my sampling clock need to be if I collect 
> data for for N seconds?

You need to get at least two times the bandwidth (Nyquist criterion).
Ie in the example above a sampling rate above 2kHz would be enough.
But:
* you need to filter out all noise outside the band you are interested
in, otherwise it gets folded in and degrades your SNR.
* you need a low jitter ADC, as the jitter requirements are set by the
signal frequency, not by the bandwidth.
* the analog part from the input to the sample and hold circuit of the
ADC need to be able to handle the high frequencies of your signal.


> Is "stable" the right term?  What's the right way to think about the question 
> I'm trying to ask?

That i cannot say, as i dont know what you are asking :-)

In this case, i think you are asking for phase noise as well as
"short" term stability (tau < averaging time)

Calculating effects on signal processing in the precense of noise is
nothing trivial. Dont worry if you dont understand everything on the
spot or cannot form an intuitive understanding.


Hmm.. i someday have to look for a good introdcution into this stuff
that doesn't rely on a lot of math. All the books i have rely at least
on Laplace.. often on z-transformation as well. And that math isn't 
high school level anymore.


Attila Kinali

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message , "Bob Camp" writes:

>Could you generate a "lead" and a "lag" estimate of the signal (in addition
>to your "center") and integrate against each of them on the fly? If so you
>would need a *lot* less memory. I seem to recall you tried something like
>this on the one of the Loran receivers. 

The reason to use the lead/center/lag model, is that you have a moving
signal you need to track, but for timenuts purposes the signal is not
going to move more than a few microseconds over an hour, so it is
probably a better strategy to just average the heck out of the signal.

It is not even clear to me that the phase-coding helps frequency
reception at all, I tried it with the very strong phase-coding of
DCF77 and there was no statistical significance relative to heavy
duty carrier averaging.

But it clearly helps a lot with phase-determination, and for that
lead/center/lag is the way to go, but you may still want to average
for a minute, then resolve the phase using the phase-modulation,
rather than run it in real-time.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Bob Camp]

Hi

Could you generate a "lead" and a "lag" estimate of the signal (in addition
to your "center") and integrate against each of them on the fly? If so you
would need a *lot* less memory. I seem to recall you tried something like
this on the one of the Loran receivers. 

Bob

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Friday, March 16, 2012 4:23 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

In message <20120316085256.9e25deaeee4f7f8617989...@kinali.ch>, Attila
Kinali w
rites:

>Hmm... do you mean you want to store all samples of an hour and then
>avarage over it?

That would be the ideal way to do it, since it would make one heck of
a comb filter and eliminate pretty much anything else.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Hal Murray]

p...@phk.freebsd.dk said:
>> Hmm... do you mean you want to store all samples of an hour and then
>> avarage over it?

> That would be the ideal way to do it, since it would make one heck of a comb
> filter and eliminate pretty much anything else. 

That only works if your reference clock is stable enough over the collecting 
period.

I'm far from a DSP wizard.  Assume I have a signal at 100 kHz with a 
bandwidth of 1 kHz.  (or pick any numbers you like)  How many samples per 
second do I need?  How stable does my sampling clock need to be if I collect 
data for for N seconds?

Is "stable" the right term?  What's the right way to think about the question 
I'm trying to ask?



-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <20120316085256.9e25deaeee4f7f8617989...@kinali.ch>, Attila Kinali w
rites:

>Hmm... do you mean you want to store all samples of an hour and then
>avarage over it?

That would be the ideal way to do it, since it would make one heck of
a comb filter and eliminate pretty much anything else.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

Moin!

On Fri, 16 Mar 2012 07:09:05 +
"Poul-Henning Kamp"  wrote:

> In message <20120315234624.a2da94430a247d235ca68...@kinali.ch>, Attila Kinali 
> writes:

> >On the other hand, if you dont have to support an OS and work on the
> >bare metal, you can get away with very little RAM. 128k is a damn lot
> >if you have to fill it with usefull data structures ;-)
> 
> Well, if you want to do full-FRI averaging for a loran-chain, you need
> something like 99600*2 * 4 = 800Kb.  If you want to do the full-hour
> averaging the WWVB doc talks about or DCF77 full-second phase-code,
> you need 2 MB for just the buffer.

Hmm... do you mean you want to store all samples of an hour and then
avarage over it? I think it would be better to just store phase offset
points for every second and then avarage over this. That would require
much less storage.

 
> >> USB2 interface 
> >
> >Which would mean you need a pretty recent chip as HighSpeed USB has not
> >been introduced into the uC world for more than 2 years or so.
> 
> USB2, not USB3.

I'm not talking about SuperSpeed. USB2 support has been around for
quite some time in ARM7 class uC. But USB2 does not mean you support
a certain speed, just the data structures follow the revised standard.
Yes, USB2 introduced the HighSpeed mode (the 480Mbit/s), but below
ARM9/MIPS class CPUs it wasn't supported until about 2-3 years ago.
AFAIK the Atmel SAM3U was one of the first Cortex-M3 with HighSpeed
support available in volumes... and that was IIRC late 2009, early 2010.

And the number of uC's with HighSpeed support isn't that large yet.


Attila Kinali

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
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Re: [time-nuts] WWVB BPSK Receiver Project?

[Poul-Henning Kamp]

In message 
, Chris Albertson writes:

>But you are right in that using dttsp [...] GNU Radio

If the objective here is time-nuttery, both of these are badly suited
because they are built to extract the rapidly changing information,
not for long averages of carrier phase.


-- 
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Re: [time-nuts] WWVB BPSK Receiver Project?

[Poul-Henning Kamp]

In message 
, Chris Albertson writes:

>That would be big expensive filter.   All you really need is the
>average of the last N samples.

Expensive ?  2kB of memory ?  Not even close to expensive.

> But with a 24b-t ADC you may not need AGC

16 bits has meant that I never needed AGC.

-- 
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Re: [time-nuts] WWVB BPSK Receiver Project?

[Poul-Henning Kamp]

In message 

, Azelio Boriani writes:

>I'm interested in your circular averaging buffer: suppose 1K long, the 1st
>sample goes into position 0, the 2nd into 1 ... the 1000th into 999 or, the
>1st gets scaled and then summed with that already present in position 0
>then the result back in position 0? And so on, of course, for position 1, 2
>...

Yes.

And once you have filled a few seconds into the buffer, you can multiply
each of the 1000 locations with a n*sine and n*cosine, and sum the results
and you have a phase vector for the signal at n KHz.

For signals like DCF77 on half kHz grid, you need a 2 msec = 2000 samples
long buffer.

-- 
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p...@freebsd.org | TCP/IP since RFC 956
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message <20120315234624.a2da94430a247d235ca68...@kinali.ch>, Attila Kinali w
rites:

>How good would that DAC need to be?

Depends on the level of ambition ?

>> 1-4MB RAM
>
>over a 256kB RAM it's get pretty thin if you want to stay in the uC
>busines. Unless you want to use an ARM9 or better with external SDRAM
>and Flash. But those are mostly BGA (very few QFP chips out there) and
>they are assumed to run Linux or Windows CE on them... Support for bare
>metal stuff is pretty thin.

There is no problem running bare-metal on ARM9's, I've done it.

But heck, it would be even better if you could load an OS on it, and
still get your bits through.

>On the other hand, if you dont have to support an OS and work on the
>bare metal, you can get away with very little RAM. 128k is a damn lot
>if you have to fill it with usefull data structures ;-)

Well, if you want to do full-FRI averaging for a loran-chain, you need
something like 99600*2 * 4 = 800Kb.  If you want to do the full-hour
averaging the WWVB doc talks about or DCF77 full-second phase-code,
you need 2 MB for just the buffer.

>> USB2 interface 
>
>Which would mean you need a pretty recent chip as HighSpeed USB has not
>been introduced into the uC world for more than 2 years or so.

USB2, not USB3.


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project?

[J. Forster]

Frankly, my dear, I'd rather be a generalist.

-John



> On 3/15/12 8:10 AM, J. Forster wrote:
>> Why make it simple when complicated also works?
>>
>> -John
>
> Can't get your doctorate doing something someone else has already
> done...
>>
>
>>>
>>> Enormous literature out there on this, and it's been grist for many a
>>> Master's or PhD dissertation.
>>> All in a quest to get ever closer to the Shannon limit...
>>>
>
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Re: [time-nuts] WWVB BPSK Receiver Project?

[Jim Lux]

On 3/15/12 9:41 PM, Chris Albertson wrote:

On Thu, Mar 15, 2012 at 8:45 PM, Jim Lux  wrote:




http://dttsp.sourceforge.net/



documentation for dttsp is less than wonderful

  
http://www.oz9aec.net/index.**php/gnu-radio/grc-examples




seems to be a bit more diverse usage for gnuradio, so more examples and
documentation



dttsp has by far the larger in-use user based because it is the engine used
by PowerSDR by Flex Radio.  It is also used by the HPSDR group.  See these
links
http://www.flex-radio.com/
http://openhpsdr.org/

But you are right in that using dttsp is something that might take a long
tome to learn.   The above user group tends to have many "appliance users"
and a few programers so learning is not so much of an issue


If there are more than half a dozen people actually using dttsp, in the 
sense of modifying it, or doing something other than creating a UI for 
it, I'd be pretty surprised.  It's pretty much a product of the two main 
authors.  As you say, the learning curve is exceedingly steep, 
especially if you want to understand the architecture and internal 
structure.  You could probably go in and do "spot changes" without 
breaking too much, but any sort of radical change (like adding a new 
demodulator) would be a pretty big challenge.


The fact that it's the core of PowerSDR means that over the years, it's 
had a lot of customization for that particular application.  Someone 
trying to decode PSK WWVB isn't going to be interested in the latency of 
the CW keyer or the performance of the automated notch filter.





GNU Radio is popular in Universities where as soon as something works they
toss it out.   It's quite a bit easier to program or if you like there is
GRC that allows visual programming.I think this is better because it
allows a wider number of people to contribute.


it's much more "componentized" and the source of the components is broader.

Probably not as "finished" as something like PowerSDR, but much easier 
to bite off small chunks.


For simple tasks, there are also tools like DL4YHF(?) spectrumlab.
http://www.qsl.net/d/dl4yhf/spectra1.html
it has:
# Decoder for some time-code transmitters: MSF(60kHz), HBG(75kHz), DCF77 
(77.5kHz) can now be used to set your PC clock to a high accuracy. All 
you need is your longwave receiver and the soundcard.
# Modulator and decoder for some 'experimental' digital communication 
modes like PSK31, BPSK, QPSK, FSK,  multi-tone HELL, MSK (minimum shift 
keying since 2004-12), transmission and reception of letters with a 
small 'terminal' window.


I've used it a lot for a variety of tasks (a Doppler radar, for one thing)



My suggestion to use a platform where these two libraries run was really to
say that you should not write this on bare hardware.  It's a good way to
paint yourself into a corner and have to start over to add some new feature
we can't think of today.



Another idea, if you have access (e.g. student licenses or thru work) is 
Matlab/Simulink and real-time-workshop.


All the building blocks are there, you just hook them up.

Pretty pricey if you're not in the educational bucket, though.  And 
Octave doesn't really have all the cool toolboxes that Matlab does.


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Re: [time-nuts] WWVB BPSK Receiver Project?

[Chris Albertson]

On Thu, Mar 15, 2012 at 8:45 PM, Jim Lux  wrote:

>
>> http://dttsp.sourceforge.net/
>>
>
> documentation for dttsp is less than wonderful
>
>  
> http://www.oz9aec.net/index.**php/gnu-radio/grc-examples
>>
>
> seems to be a bit more diverse usage for gnuradio, so more examples and
> documentation
>

dttsp has by far the larger in-use user based because it is the engine used
by PowerSDR by Flex Radio.  It is also used by the HPSDR group.  See these
links
http://www.flex-radio.com/
http://openhpsdr.org/

But you are right in that using dttsp is something that might take a long
tome to learn.   The above user group tends to have many "appliance users"
and a few programers so learning is not so much of an issue

GNU Radio is popular in Universities where as soon as something works they
toss it out.   It's quite a bit easier to program or if you like there is
GRC that allows visual programming.I think this is better because it
allows a wider number of people to contribute.

My suggestion to use a platform where these two libraries run was really to
say that you should not write this on bare hardware.  It's a good way to
paint yourself into a corner and have to start over to add some new feature
we can't think of today.


Chris Albertson
Redondo Beach, California
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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Jim Lux]

On 3/15/12 3:27 PM, Poul-Henning Kamp wrote:

In message, Marek Peca writes:



Yes, it should work on any USB audio capable OS, ie. Linux, Windows, MacOS etc.


I would like to recommend against this approach for a number of reasons.

First, yes, while you can do undersampling and such, it puts very high
requirements on your analog filters.

The reason I use 1MSPS is that it allows me to use a very sloppy low-pass
filter filter which just cuts off somewhere around 150-200 kHz, and do
everything else in software.


and if you have any sort of processing behind the 1MSPS, you can do a 
simple digital filter and decimate.




This means that I have no phase/group-delay distortion in the analog
part that I need to compensate in software.

It also means that I don't have to change hardware to play with different
signals, they're all there, all the time, for instance the stuff under
http://phk.freebsd.dk/Leap/
is pulled out that way.

If I, based on my design, were to design a gadget for doing VLF
time-nuts stuff, it would be:

Floating Input trafo with center-tap for powering antenna
16 bit 1MSPS ADC
ARM chip
10MHz clock input
1PPS sync input
1PPS sync output
(DAC output for {Rb|Ocxo}DO use ?)
1-4MB RAM
USB2 interface

Sending 2MB/s through a serial port profile is not a big problem
for USB2 or for that matter for an operating system, so you can
easily grap full spectrum and play with your your PC, and once you
have made some of it work, you can compile the same code and and
download it to the ARM chip, and use the serial port only for
stats/summary/(Tek4010-graphs) or you can use another USB profile
or whatever.

The ARM chip is plenty powerful to do pretty much anything you
are to on its own once you give it the code to do so.




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Re: [time-nuts] WWVB BPSK Receiver Project?

[Jim Lux]

On 3/15/12 3:24 PM, Chris Albertson wrote:

On Thu, Mar 15, 2012 at 2:51 PM, Attila Kinali  wrote:


After the discussion here, i had a similar idea. I want to use the
STM32F4xx for something bigger and bought two discovery boards to get
used to them. But i didn't know what i want to do... it should be something
usefull.. at least half way usefull. And the discussion here prodded
me that i could do a SDR DCF77 with that. A 160MHz 32bit uC with hardware
single precision floatingpoint is way more than fast enough to handle that :-


You might want to choose a platform that can run either dttsp or
Gnuradio/GRC or else you will be writing from scratch.  You will spend
weeks doing what could be done in hours.  Look at these
http://dttsp.sourceforge.net/


documentation for dttsp is less than wonderful


http://www.oz9aec.net/index.php/gnu-radio/grc-examples


seems to be a bit more diverse usage for gnuradio, so more examples and 
documentation




Chris Albertson
Redondo Beach, California

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Jim Lux]

On 3/15/12 8:10 AM, J. Forster wrote:

Why make it simple when complicated also works?

-John


Can't get your doctorate doing something someone else has already 
done...






Enormous literature out there on this, and it's been grist for many a
Master's or PhD dissertation.
All in a quest to get ever closer to the Shannon limit...



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Re: [time-nuts] WWVB BPSK Receiver Project?

[Chris Albertson]

That would be big expensive filter.   All you really need is the
average of the last N samples.
But with WWVB the bits are amplitude modulated at one bit per second.
so you want a big time constant on any AGC, maybe 100 seconds.   If
you are sampling at 192K that would use way to much memory if you
stored each sample.  Better to only keep running statistics.For
AGC you don't need to process every sample, you can feed the AGC a
subset of the sample stream. But with a 24b-t ADC you may not need
AGC

On Thu, Mar 15, 2012 at 4:01 PM, Azelio Boriani
 wrote:
> PHK,
> I'm interested in your circular averaging buffer: suppose 1K long, the 1st
> sample goes into position 0, the 2nd into 1 ... the 1000th into 999 or, the
> 1st gets scaled and then summed with that already present in position 0
> then the result back in position 0? And so on, of course, for position 1, 2
> ...
>
> On Thu, Mar 15, 2012 at 11:48 PM, Chris Albertson > wrote:
>
>> On Thu, Mar 15, 2012 at 3:13 PM, Poul-Henning Kamp 
>> wrote:
>> > In message <20120315152620.8347488e049854218aed4...@kinali.ch>, Attila
>> Kinali w
>> > rites:
>> >
>> >>> Do you need 16 bits or can you get by with a 12 bit ADC?
>> >
>> > In general: The more the merrier, for a digital dude like me, having
>> > more bits is easier than getting AGC working correctly :-)
>> >
>> >>> Have you considered using an FPGA for signal processing? It seems
>> >> you need a fairly serious CPU to handle that much data.
>>
>>
>> "That much data" we are talking about 192K samples per second.   I can
>> routinely record multiple tracks of 192K audio and do processing in
>> real time and the CPU meter hardly moves  the bottom.    Even a
>> gigabit per second Ethernet port is not "a lot of data" on a modern
>> computer.
>>
>> FPGAs and DSP come into play if you are talking about tens of millions
>> of samples per second with data rates above say 200Mb/Sec  But the
>> rate from an audio interface running 192K and 24-bits is still under
>> one megabyte per second.    An interesting ratio is the number of CPU
>> cycles available to process one sample.  On my Apple iMac that would
>> be about roughly  200,000 operations per data sample.
>>
>> In real life SDR receivers even an older CPU can process the I and Q
>> channels and maintain a large graphic screen and send and receive data
>> over a network and still not be "maxed out"
>>
>>
>> Chris Albertson
>> Redondo Beach, California
>>
>> ___
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>>
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-- 

Chris Albertson
Redondo Beach, California

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Azelio Boriani]

PHK,
I'm interested in your circular averaging buffer: suppose 1K long, the 1st
sample goes into position 0, the 2nd into 1 ... the 1000th into 999 or, the
1st gets scaled and then summed with that already present in position 0
then the result back in position 0? And so on, of course, for position 1, 2
...

On Thu, Mar 15, 2012 at 11:48 PM, Chris Albertson  wrote:

> On Thu, Mar 15, 2012 at 3:13 PM, Poul-Henning Kamp 
> wrote:
> > In message <20120315152620.8347488e049854218aed4...@kinali.ch>, Attila
> Kinali w
> > rites:
> >
> >>> Do you need 16 bits or can you get by with a 12 bit ADC?
> >
> > In general: The more the merrier, for a digital dude like me, having
> > more bits is easier than getting AGC working correctly :-)
> >
> >>> Have you considered using an FPGA for signal processing? It seems
> >> you need a fairly serious CPU to handle that much data.
>
>
> "That much data" we are talking about 192K samples per second.   I can
> routinely record multiple tracks of 192K audio and do processing in
> real time and the CPU meter hardly moves  the bottom.Even a
> gigabit per second Ethernet port is not "a lot of data" on a modern
> computer.
>
> FPGAs and DSP come into play if you are talking about tens of millions
> of samples per second with data rates above say 200Mb/Sec  But the
> rate from an audio interface running 192K and 24-bits is still under
> one megabyte per second.An interesting ratio is the number of CPU
> cycles available to process one sample.  On my Apple iMac that would
> be about roughly  200,000 operations per data sample.
>
> In real life SDR receivers even an older CPU can process the I and Q
> channels and maintain a large graphic screen and send and receive data
> over a network and still not be "maxed out"
>
>
> Chris Albertson
> Redondo Beach, California
>
> ___
> time-nuts mailing list -- time-nuts@febo.com
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Re: [time-nuts] WWVB BPSK Receiver Project?

[Chris Albertson]

On Thu, Mar 15, 2012 at 3:13 PM, Poul-Henning Kamp  wrote:
> In message <20120315152620.8347488e049854218aed4...@kinali.ch>, Attila Kinali 
> w
> rites:
>
>>> Do you need 16 bits or can you get by with a 12 bit ADC?
>
> In general: The more the merrier, for a digital dude like me, having
> more bits is easier than getting AGC working correctly :-)
>
>>> Have you considered using an FPGA for signal processing? It seems
>> you need a fairly serious CPU to handle that much data.


"That much data" we are talking about 192K samples per second.   I can
routinely record multiple tracks of 192K audio and do processing in
real time and the CPU meter hardly moves  the bottom.Even a
gigabit per second Ethernet port is not "a lot of data" on a modern
computer.

FPGAs and DSP come into play if you are talking about tens of millions
of samples per second with data rates above say 200Mb/Sec  But the
rate from an audio interface running 192K and 24-bits is still under
one megabyte per second.An interesting ratio is the number of CPU
cycles available to process one sample.  On my Apple iMac that would
be about roughly  200,000 operations per data sample.

In real life SDR receivers even an older CPU can process the I and Q
channels and maintain a large graphic screen and send and receive data
over a network and still not be "maxed out"


Chris Albertson
Redondo Beach, California

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Attila Kinali]

On Thu, 15 Mar 2012 22:27:53 +
"Poul-Henning Kamp"  wrote:

> If I, based on my design, were to design a gadget for doing VLF
> time-nuts stuff, it would be:
> 
> Floating Input trafo with center-tap for powering antenna
> 16 bit 1MSPS ADC
> ARM chip 
> 10MHz clock input
> 1PPS sync input
> 1PPS sync output
> (DAC output for {Rb|Ocxo}DO use ?)

How good would that DAC need to be?

> 1-4MB RAM

over a 256kB RAM it's get pretty thin if you want to stay in the uC
busines. Unless you want to use an ARM9 or better with external SDRAM
and Flash. But those are mostly BGA (very few QFP chips out there) and
they are assumed to run Linux or Windows CE on them... Support for bare
metal stuff is pretty thin.

On the other hand, if you dont have to support an OS and work on the
bare metal, you can get away with very little RAM. 128k is a damn lot
if you have to fill it with usefull data structures ;-)


> USB2 interface 

Which would mean you need a pretty recent chip as HighSpeed USB has not
been introduced into the uC world for more than 2 years or so.


Attila Kinali

-- 
Why does it take years to find the answers to
the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Poul-Henning Kamp]

In message , Marek Peca writes:


>Yes, it should work on any USB audio capable OS, ie. Linux, Windows, MacOS etc.

I would like to recommend against this approach for a number of reasons.

First, yes, while you can do undersampling and such, it puts very high
requirements on your analog filters.

The reason I use 1MSPS is that it allows me to use a very sloppy low-pass
filter filter which just cuts off somewhere around 150-200 kHz, and do
everything else in software.

This means that I have no phase/group-delay distortion in the analog
part that I need to compensate in software.

It also means that I don't have to change hardware to play with different
signals, they're all there, all the time, for instance the stuff under
http://phk.freebsd.dk/Leap/
is pulled out that way.

If I, based on my design, were to design a gadget for doing VLF
time-nuts stuff, it would be:

Floating Input trafo with center-tap for powering antenna
16 bit 1MSPS ADC
ARM chip 
10MHz clock input
1PPS sync input
1PPS sync output
(DAC output for {Rb|Ocxo}DO use ?)
1-4MB RAM
USB2 interface 

Sending 2MB/s through a serial port profile is not a big problem
for USB2 or for that matter for an operating system, so you can
easily grap full spectrum and play with your your PC, and once you
have made some of it work, you can compile the same code and and
download it to the ARM chip, and use the serial port only for
stats/summary/(Tek4010-graphs) or you can use another USB profile
or whatever.

The ARM chip is plenty powerful to do pretty much anything you
are to on its own once you give it the code to do so.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Chris Albertson]

On Thu, Mar 15, 2012 at 2:51 PM, Attila Kinali  wrote:

> After the discussion here, i had a similar idea. I want to use the
> STM32F4xx for something bigger and bought two discovery boards to get
> used to them. But i didn't know what i want to do... it should be something
> usefull.. at least half way usefull. And the discussion here prodded
> me that i could do a SDR DCF77 with that. A 160MHz 32bit uC with hardware
> single precision floatingpoint is way more than fast enough to handle that :-

You might want to choose a platform that can run either dttsp or
Gnuradio/GRC or else you will be writing from scratch.  You will spend
weeks doing what could be done in hours.  Look at these
http://dttsp.sourceforge.net/
http://www.oz9aec.net/index.php/gnu-radio/grc-examples

Chris Albertson
Redondo Beach, California

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Poul-Henning Kamp]

In message <20120315152620.8347488e049854218aed4...@kinali.ch>, Attila Kinali w
rites:

>> Do you need 16 bits or can you get by with a 12 bit ADC?

In general: The more the merrier, for a digital dude like me, having 
more bits is easier than getting AGC working correctly :-)

>> Have you considered using an FPGA for signal processing? It seems
> you need a fairly serious CPU to handle that much data.

I have considered FPGA, DSP would probably be more suitable, but
if I can do it in an ARM with C/Assy code, I prefer that.

>I think Poul-Henning is refering to his AducLoran receiver, 

That's one of the few experiements I bothered to document, I've been
doing similar stuff with DCF77 phase-code etc.

As long as you're after time/freq, you can use very deep averaging
which only takes a few instructions per sample, so for instance
the 42MHz Aduc7026 chip copes nicely with a single Loran-C signal.

I think I could squeeze a Loran-C navigation solution into it, if
I wanted to and as long as we're not talking too high speeds (again
allowing deep averaging) but I have not bothered.

A modern PC has a lot of computing power for stuff like this, and
is great for prototyping code, before dumping into a smaller chip.

That's how I found out that the circular-buffer averaging comb-filter
is a much better and stronger signal discriminator than almost anything
else you can come up with, for frequency/phase reception.

See for instance: http://phk.freebsd.dk/loran-c/CW/

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Attila Kinali]

On Thu, 15 Mar 2012 22:51:55 +0100
Attila Kinali  wrote:

> > Of course I mean it should pick your 60kHz, as well as other systems known 
> > to 
> > me: Japanese 40kHz, 60kHz, Swiss 75kHz, British 60kHz and possibly others. 
> > Highly unsure about Russian 25kHz, even do not know, whether it is still on 
> > air.
> 
> HBG has been switched of earlier this year. So DCF77 and Alison are the
> only time LF senders left in continental europe.

Err,, it's Allouis. Don't ask me where that Alison came from...

Attila Kinali
-- 
Why does it take years to find the answers to
the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Attila Kinali]

On Thu, 15 Mar 2012 20:02:31 +0100 (CET)
Marek Peca  wrote:

> Of course I mean it should pick your 60kHz, as well as other systems known to 
> me: Japanese 40kHz, 60kHz, Swiss 75kHz, British 60kHz and possibly others. 
> Highly unsure about Russian 25kHz, even do not know, whether it is still on 
> air.

HBG has been switched of earlier this year. So DCF77 and Alison are the
only time LF senders left in continental europe.

 
> 1. first, deliver simple USB audio sampling unit with 77.5kHz-proven ferrite 
> rod preamplifier, ready to work with 40..80kHz signals at least;
> every processing within PC / Gnuradio framework;

After the discussion here, i had a similar idea. I want to use the
STM32F4xx for something bigger and bought two discovery boards to get
used to them. But i didn't know what i want to do... it should be something
usefull.. at least half way usefull. And the discussion here prodded
me that i could do a SDR DCF77 with that. A 160MHz 32bit uC with hardware
single precision floatingpoint is way more than fast enough to handle that :-)

If i've time, i sketch the HW this weekend and build it as soon as i've
time... And then it's just software :-)

Attila Kinali

-- 
Why does it take years to find the answers to
the questions one should have asked long ago?

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Chris Albertson]

The major advantage of simply sampling at 192K is that it is so
simple.  Not much hardware outside of a good audio interface is
required.

But the mixer is attractive because  then you can make it a quadrature
mixer and then sample with both stereo channels.   One then could use
a more common 44.1 or 48K sample rate.

You trade a bit of hardware up front for reduced processing
requirements later.


On Thu, Mar 15, 2012 at 12:38 AM, Peter Monta  wrote:
>> Many A/D converter systems use a sample and hold before the A/D converter.
>> If you do the same before your sound card (your A/D converter) and drive the 
>> S&H with an audio output from your sound
>> card, say at 6.1 kHz you would get a 1 kHz signal into your sound card to 
>> process. You can call it under sampling
>> aliasing or whatever.
>
> Yes, this would work, but instantaneous sampling would tend to alias
> in many harmonics, requiring good prefiltering at RF (if you can call
> 60 kHz RF).  Just as easy would be a mixer from CMOS switches, driven
> say at 50 kHz to get 10 kHz into the sound card.
>
> The WWVB signal apparently has a double-sided bandwidth of about 1200
> Hz (not clear from the paper if that means 3 dB bandwidth or something
> else).  To get all of the signal something like 2 or 3 kHz might be
> safest, requiring an IF of several kHz at least.
>
> Cheers,
> Peter
>
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-- 

Chris Albertson
Redondo Beach, California

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Chris Albertson]

On Thu, Mar 15, 2012 at 1:48 AM, Chuck Forsberg WA7KGX N2469R
 wrote:
> How about this:  Generate a precise 60 KHz signal from a GPSDO's 10 MHz.
> Modulate it with 1 bit audio generated by a Linux program which would know
> about DST.

The standard NTP source code distribution comes with a program to
generate the time code.  So you'd not have the write it yourself.
It's purpose is to test the the WWV drivers n NTP.   It is not built
by default, from memory the source is in a directory called "test".

But for those radio clocks in your house the new WWVB signal should
just work.   They will not notice the phase modulation
Chris Albertson
Redondo Beach, California

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Re: [time-nuts] WWVB BPSK Receiver Project? (fwd)

[Marek Peca]

Forgot to Cc: the maillist, sorry. So, FYI:

-- Forwarded message --
Date: Thu, 15 Mar 2012 16:31:14 +0100 (CET)
From: Marek Peca 
To: David J Taylor 
Subject: Re: [time-nuts] WWVB BPSK Receiver Project?

Hello,

I would perhaps be interested in something which would pick up our local 60 
KHz transmissions, and having a USB interface would be OK.  However, all my 
systems are Windows, so whatever software was produced would have to work on 
Windows.


Of course I mean it should pick your 60kHz, as well as other systems known to 
me: Japanese 40kHz, 60kHz, Swiss 75kHz, British 60kHz and possibly others. 
Highly unsure about Russian 25kHz, even do not know, whether it is still on 
air.


Yes, it should work on any USB audio capable OS, ie. Linux, Windows, MacOS etc.

I take it that you are thinking of all the detection and processing in the 
PC?  I would prefer as much processing as possible to be in the device, and 
that it perhaps output serial data over the USB port, looking like a GPS.  Is 
that too much to ask?


Well, I will tell you, what I would like to do in larger picture:

1. first, deliver simple USB audio sampling unit with 77.5kHz-proven ferrite 
rod preamplifier, ready to work with 40..80kHz signals at least;

every processing within PC / Gnuradio framework;

BUT

2. be ready to upgrade a firmware of the board to do all the PRBS BPSK tracking 
etc. within the board's MCU and deliver at least 1pps output, preferably also 
sinewave LF-locked output (range 100kHz..1MHz) for further processing.


So, I mean, the board will work in PC-based SDR mode in first iteration, and 
after all the processing will be proven by multiple users, we can then switch 
to better firmware, which will do basic tasks even without the PC.



I think I can provide basic firmware by myself, for more elaborate things it 
seems to me the best solution is to start our common open-source project.


However, the board's MCU will accept anyone's firmware, anyway.


Please, tell me your oppinion.
I would like to know, whether to put some time into development,
so if there are really some people, who would appreciate such a
LF-SDR-USB kit.


Best regards,
Marek

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Bob Camp]

Hi

If you can handle the data rates for Loran at 100 KHz with a micro, then you
should be able to handle the data rates for something at 60 KHz. My guess is
that a simple "I know what the waveform is now compare it" approach would
not be terribly processor intensive. Put another way, you can easily predict
exactly what the signal will be doing at any instant. You just need to steer
to the error from that prediction.

Bob

-Original Message-
From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On
Behalf Of Attila Kinali
Sent: Thursday, March 15, 2012 10:26 AM
To: shali...@gmail.com; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] WWVB BPSK Receiver Project?

On Thu, 15 Mar 2012 13:50:08 +
shali...@gmail.com wrote:

> Poul-Henning,
> 
> Do you need 16 bits or can you get by with a 12 bit ADC?
> 
> Have you considered using an FPGA for signal processing? It seems you need
a fairly serious CPU to handle that much data.
> 

I think Poul-Henning is refering to his AducLoran receiver, which
used a 1Msps ADC [1]. I dont remember what he exactly does with the signal,
but IIRC he uses a 40MHz uC which leaves him with 40 Cycles per sample,
which is quite a lot if you only do just some math calculation to detect
the start of a second...

And unlike with the FPGA, it does not take more time to process 8bit
or 24 bit samples as the uC works with 32bit numbers anyways.


Attila Kinali


[1] http://phk.freebsd.dk/AducLoran/

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin

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Re: [time-nuts] WWVB BPSK Receiver Project?

[Attila Kinali]

On Thu, 15 Mar 2012 07:49:15 -0700 (PDT)
"J. Forster"  wrote:

> Suppose the modulation is not present. The output of the phase detector
> that steers the local standard ot indicator works correctly.
> 
> Now reverse the 60 kHz carrier. The phase detector works exactly thye
> opposite way...  wrong.
> 
> Now alternate between 0 and 190 degrees.
> 
> The loop alternate works between exactly right and exactly wrong...  it
> dithers around and the output is a measure of the ratio of 1's to 0's and
> is utterly useless.

That under the assumption, that they do not make sure that the average
phase is zeros out (or converges to 90°). I have not found anything
taht suggests this... on the other hand, there is nothing that suggests
the contrary either.

But you didnt address my main point yet: The phase of the WWVB signal
is already fluctuating a lot, just by natural occuring atmospherical
"noise". If a 180° phase shift does destabilize your PLL, what does
these "shifts" which are much larger do?

Attila Kinali

-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin

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Re: [time-nuts] WWVB BPSK Receiver Project?

[J. Forster]

Why make it simple when complicated also works?

-John





> On 3/15/12 7:49 AM, J. Forster wrote:
>> Suppose the modulation is not present. The output of the phase detector
>> that steers the local standard ot indicator works correctly.
>>
>> Now reverse the 60 kHz carrier. The phase detector works exactly thye
>> opposite way...  wrong.
>>
>> Now alternate between 0 and 190 degrees.
>>
>> The loop alternate works between exactly right and exactly wrong...  it
>> dithers around and the output is a measure of the ratio of 1's to 0's
>> and
>> is utterly useless.
>>
>
> and the cleverness of the  Costas loop is that it uses (an estimate of)
> the current data bit (the output of the I arm) to flip the sign of the
> error signal from the quadrature arm.
>
> There's a lot of scope for modification of the basic linear Costas loop.
>   Hard/soft limiters in either or both arms, you've got three filters
> (the two arm filters and the loop filter) to fool with, plus all sorts
> of schemes using "data aiding" where you get feedback from your symbol
> slicer to help do a better job on the carrier tracking.
>
> You can also run your loop with hard limited signal input (makes the
> "mixers" turn into XOR gates).
>
> If you don't need the bits in real time (i.e. you can tolerate some
> latency), then you can also build tracking loops that effectively "look
> into the future"; i.e. make decisions on carrier and bit at time t using
> future data from t>now, as well as t=[-infinity, now].
>
>
> Enormous literature out there on this, and it's been grist for many a
> Master's or PhD dissertation.
> All in a quest to get ever closer to the Shannon limit...
>
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Re: [time-nuts] WWVB BPSK Receiver Project?

[Jim Lux]

On 3/15/12 7:49 AM, J. Forster wrote:

Suppose the modulation is not present. The output of the phase detector
that steers the local standard ot indicator works correctly.

Now reverse the 60 kHz carrier. The phase detector works exactly thye
opposite way...  wrong.

Now alternate between 0 and 190 degrees.

The loop alternate works between exactly right and exactly wrong...  it
dithers around and the output is a measure of the ratio of 1's to 0's and
is utterly useless.



and the cleverness of the  Costas loop is that it uses (an estimate of) 
the current data bit (the output of the I arm) to flip the sign of the 
error signal from the quadrature arm.


There's a lot of scope for modification of the basic linear Costas loop. 
 Hard/soft limiters in either or both arms, you've got three filters 
(the two arm filters and the loop filter) to fool with, plus all sorts 
of schemes using "data aiding" where you get feedback from your symbol 
slicer to help do a better job on the carrier tracking.


You can also run your loop with hard limited signal input (makes the 
"mixers" turn into XOR gates).


If you don't need the bits in real time (i.e. you can tolerate some 
latency), then you can also build tracking loops that effectively "look 
into the future"; i.e. make decisions on carrier and bit at time t using 
future data from t>now, as well as t=[-infinity, now].



Enormous literature out there on this, and it's been grist for many a 
Master's or PhD dissertation.

All in a quest to get ever closer to the Shannon limit...

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Re: [time-nuts] WWVB BPSK Receiver Project?

[J. Forster]

Jim wrote:

a square wave,
>> multiplied by itself, has the same output as input.
>
> Oh... I was assuming you had the two quadrature square waves (which are
> just like the saturated LO for the mixer in RF land)

You don't have two square waves in quadrature. You have the (amplified)
signal from the antenna.


>> A Costas Loop recovers the bit stream and the carrier frequency (from
>> the local VCO) from a BPSK. It is self syncronizing.
>
>
> Yes.. but if you don't care about the bitstream, and you want simpler
> hardware, squaring works. (especially if the modulator doesn't have good
> carrier suppression)

I think a better implementation would be:

Analog multiplier
Adaptive comparator (slice level = 1/2 P_P signal)
Flip Flop
Rabbit ears filter at 60 kHz

-John

=

>
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Re: [time-nuts] WWVB BPSK Receiver Project?

[J. Forster]

Suppose the modulation is not present. The output of the phase detector
that steers the local standard ot indicator works correctly.

Now reverse the 60 kHz carrier. The phase detector works exactly thye
opposite way...  wrong.

Now alternate between 0 and 190 degrees.

The loop alternate works between exactly right and exactly wrong...  it
dithers around and the output is a measure of the ratio of 1's to 0's and
is utterly useless.

-John




> On Wed, 14 Mar 2012 18:14:56 -0700
> WB6BNQ  wrote:
>
>>
>> His enthusiasm was aimed totally at new products.  Although he admitted
>> it leaves all the real Timenut type people, actually
>> using the system for its intended purpose, out in the cold, he really
>> did not seem to care.  Pointing out that a failure
>> with the GPS system left WWVB as the only alternate did not seem to
>> matter either.
>
> Could someone be so kind and could explain me what the problem with
> the BPSK modulation is? I mean the phase of WWVB shifts around several
> 10us
> during sunrise/sunset already... Not to talk about the changing
> propagation
> conditions. Just see [1] for an example of what's happening.
>
> Yes, for those devices that lock on the phase, you'd have to change
> their correction/detection loop, but overall, they should still work.
>
>
>   Attila Kinali
>
>
> [1] http://www.febo.com/time-freq/wwvb/spectracom/index.html
>
> --
> The trouble with you, Shev, is you don't say anything until you've saved
> up a whole truckload of damned heavy brick arguments and then you dump
> them all out and never look at the bleeding body mangled beneath the heap
>   -- Tirin, The Dispossessed, U. Le Guin
>
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>
>



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Re: [time-nuts] WWVB BPSK Receiver Project?

[Demian Martin]

There are a number of sound cards (and have been for 10 years now) that can
capture up to 95 KHz with extraordinary fidelity. They sample at 192 KHz and
usually have "24" bit converters good tor 20+ bits. These can capture the
complete FM MPX output pretty easily.

Some of the newer ADC's have less that .001% THD at 192 KHz sampling.  The
AK5394a for example has -105 dB THD at 1 KHz. Can be had as a chip for about
$22 ea if you want to build your own. Some current motherboards have an
SPDIF input that can handle the 192 KHz sample rate. The next challenge is
getting the OS to handle it, not difficult.
Demian


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Re: [time-nuts] WWVB BPSK Receiver Project?

[Marek Peca]

Dear american colleagues,

as I read last few posts about WWVB, I am very tempted to return to LF 
time signal fun. As I wrote you, there vere very good results using cheap 
2 IC circuitry and a PC with our local DCF77 signal.


Under influence of this maillist, I am thinking about recreating of the 
receiver using recent MCU, ferrite rod on one side, optional 10MHz input, 
USB device acting as a standard USB audio class soundcard output.
Everything working with GNUradio, MATLAB, HAM waterfalls etc. out of the 
box.


Could be used as an audio frequency front-end for HAM radio, too.

Would you be interested in such a kit? It should be <$100 all inclusive, 
if there will be more people involved (let say 5-10) to cover PCBs.



Best regards,
Marek

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