Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Poul-Henning Kamp]

In message 
, "Deirdre 
O'Byrne" writes:

>MSF disciplined oscillator?! I don't trust these receivers to any better
>than about the 20ms mark, so such a disciplined oscillator would have quite
>a long integration time!

It's actually more complicated and better than that.

The low-pass filter dominates, so the falling flank at second N
depends on the pulsewidth at second N-1.

I can't remember the numbers I got when I "sorted" DCF77 pulses depending
on the previous pulse being short or long, but it was a fair bit better
than 20ms.

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Re: [time-nuts] eBay GPS antenna.

[Bob kb8tq]

Hi

If you spend some “quality time” with the pictures in the listing, the antenna
is indeed labeled “operating voltage 3.3 to 18V”. Yes, I find that a bit 
incredible.
If there is nonsense being generated, it’s not by the person listing the 
antenna 
on eBay.  My guess would be that the automotive world has pushed some odd
semiconductor outfit to tool up a regulator that does what’s needed.

Bob

> On Feb 6, 2018, at 4:03 PM, John Green  wrote:
> 
> I kind of have to believe the specs. The two survey grade antennas I
> already have, a Leica and a Trimble, both have regulators in the preamp
> sections. The Leica has an 8 volt one and the Trimble has a 5 volt one. I
> intend to hook it up to a variable supply and watch the current as I
> increase voltage. If it has a regulator, the current should stabilize at an
> input voltage just above what the internal preamp operates at. If not, it
> should continue to rise. I am tempted to pry it apart, even if it risks
> damage just so I can see for myself what they are using for the preamp
> stages.
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Deirdre O'Byrne]

>
>
> Splitting the MSF received signal into 100ms chunks, all of the seconds
> apart from the start-of-minute marker are of the form 0AB1. Using "x"
> to represent a 100ms chunk whose value could not be determined, I notice
> that many of the received seconds were of the form "0AB1x111" or "0AB11x11"
> etc - i.e. there was only one 100ms chunk within the second whose value
> could not be reliably determined and whose value was non-critical.
>

Ooops - apologies - this referred to another algorithm I investigated, and
makes no sense in the context of this algorithm.

Still I believe a blame algorithm would recover a lot of lost data. It
would require a shift register 1,200 wide - with each slot representing the
value during a 100ms interval from achosen edge.

Thanks.
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Deirdre O'Byrne]

>
>
> Did MSF finally go to a BPSK signal format? I heard they were considering
> that.
>

I don't know, though I've ordered a SDR which should be able to receive the
raw signal. I don't see anything about it in the documentation, though.

Regards,
Deirdre.
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Bob kb8tq]

Hi

> On Feb 6, 2018, at 3:48 PM, Deirdre O'Byrne  wrote:
> 
> Tom,
> 
> Thanks for the feedback!
> 
> On 6 February 2018 at 20:29, Tom Van Baak  wrote:
> 
>> 
>> 2) Not all decoding errors are equal. Since this is a time code instead of
>> arbitrary binary data you can use the internal structure of the data to
>> your benefit.
>> 
> 
> As I said to Poul-Henning, that is the next level of error detection, which
> also has application in error correcting some of the "almost-right" signals.
> 
> 
>> 3) A side-effect of your data set is that you can track performance of the
>> oscillator inside the logic analyzer: convert the 700k GPS timestamps into
>> interval, find and replace the 4 glitch lines with 2 lines of 1.000150, and
>> then use Stable32 or TimeLab to plot. I used a 10 minute running average to
>> reduce the 50 us quantization noise. Note the mean frequency of your
>> timebase is 152 ppm low.
> 
> 
> I made it out to be 152.2ppm, which is kinda disappointing. But the signal
> analyser cost very little, and you get what you pay for.
> 
> I have not yet wrapped my head around how to create ADEV plots, so thanks
> for your work on that - it's interesting to see that (presumed) initial
> thermal effect.
> 
> 
>> Over 8 days this results in a cumulative sampling error of 105 seconds. If
>> your decoding algorithms are relative instead of absolute this won't be a
>> problem. OTOH, you may be able to use your decoding process to detect this
>> drift and then compensate for it in software. You have the beginnings of a
>> MSF-Disciplined-Oscillator project.
>> 
> 
> MSF disciplined oscillator?! I don't trust these receivers to any better
> than about the 20ms mark, so such a disciplined oscillator would have quite
> a long integration time!

Once upon a time, that *was* how people did disciplined oscillators. Part of the
answer to “how?” is that their target accuracies were not as tight as what we 
now
think of as normal. 

Bob


> 
> Thanks again.
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Hal Murray]

deirdre@gmail.com said:
> MSF disciplined oscillator?! I don't trust these receivers to any better
> than about the 20ms mark, so such a disciplined oscillator would have quite
> a long integration time! 

It would be interesting to see if you can find any pattern in your histogram 
plots.  Say, time of day.

What happens if you average over 10 or 100 samples?


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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Deirdre O'Byrne]

Tom,

Thanks for the feedback!

On 6 February 2018 at 20:29, Tom Van Baak  wrote:

>
> 2) Not all decoding errors are equal. Since this is a time code instead of
> arbitrary binary data you can use the internal structure of the data to
> your benefit.
>

As I said to Poul-Henning, that is the next level of error detection, which
also has application in error correcting some of the "almost-right" signals.


> 3) A side-effect of your data set is that you can track performance of the
> oscillator inside the logic analyzer: convert the 700k GPS timestamps into
> interval, find and replace the 4 glitch lines with 2 lines of 1.000150, and
> then use Stable32 or TimeLab to plot. I used a 10 minute running average to
> reduce the 50 us quantization noise. Note the mean frequency of your
> timebase is 152 ppm low.


I made it out to be 152.2ppm, which is kinda disappointing. But the signal
analyser cost very little, and you get what you pay for.

I have not yet wrapped my head around how to create ADEV plots, so thanks
for your work on that - it's interesting to see that (presumed) initial
thermal effect.


> Over 8 days this results in a cumulative sampling error of 105 seconds. If
> your decoding algorithms are relative instead of absolute this won't be a
> problem. OTOH, you may be able to use your decoding process to detect this
> drift and then compensate for it in software. You have the beginnings of a
> MSF-Disciplined-Oscillator project.
>

MSF disciplined oscillator?! I don't trust these receivers to any better
than about the 20ms mark, so such a disciplined oscillator would have quite
a long integration time!

Thanks again.
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Re: [time-nuts] eBay GPS antenna.

[John Green]

I kind of have to believe the specs. The two survey grade antennas I
already have, a Leica and a Trimble, both have regulators in the preamp
sections. The Leica has an 8 volt one and the Trimble has a 5 volt one. I
intend to hook it up to a variable supply and watch the current as I
increase voltage. If it has a regulator, the current should stabilize at an
input voltage just above what the internal preamp operates at. If not, it
should continue to rise. I am tempted to pry it apart, even if it risks
damage just so I can see for myself what they are using for the preamp
stages.
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Poul-Henning Kamp]

In message <20180206225742.67030406...@ip-64-139-1-69.sjc.megapath.net>, Hal 
Murray writes:
>> Since MSF *is* on 60 KHz, you do indeed get dead spots.
>
>If the two signals are not encoded identically, there should be an 
>interesting signal when one of the transmitters is off and the other is on.  
>Has anybody looked for that sort of pattern?

I have seen signs of that in my data in the shape of phase-shifts,
and that sort of made me concentrate on DCF & LORAN.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Bob kb8tq]

Hi

If you look at the papers for the “new” WWVB format, there are plots of where 
the
MSF issues are likely to be the greatest. Since both signals are phase and 
amplitude
 shifted by propagation effects, you will not get stationary nulls. You simply 
get zones
where the reception is tough. 

Bob

> On Feb 6, 2018, at 5:57 PM, Hal Murray  wrote:
> 
>> Since MSF *is* on 60 KHz, you do indeed get dead spots.
> 
> If the two signals are not encoded identically, there should be an 
> interesting signal when one of the transmitters is off and the other is on.  
> Has anybody looked for that sort of pattern?
> 
> Is there a map of the dead spots?  Any time-nuts live in/near one?
> 
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Hal Murray]

> Since MSF *is* on 60 KHz, you do indeed get dead spots.

If the two signals are not encoded identically, there should be an 
interesting signal when one of the transmitters is off and the other is on.  
Has anybody looked for that sort of pattern?

Is there a map of the dead spots?  Any time-nuts live in/near one?



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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Bob kb8tq]

Hi

> On Feb 6, 2018, at 4:19 PM, Poul-Henning Kamp  wrote:
> 
> 
> In message 
> , 
> "Deirdre O'Byrne" writes:
> 
>> With a blame algorithm in place it should be possible to recover these 
>> signals.
> 
> Yes, easily.
> 
> At distance MSF is significantly harder to receive than DCF77.
> 
> One of the reasons is that USA also operates two 60kHz transmitters
> also very precisely on frequency, so there are areas of the world
> where the three signals cancel and areas where they reinforce
> each other.

I believe we only have one transmitter on the air at 60 KHz in the US. The 
Japanese do indeed operate multiple transmitters on the same frequency 
( 40 KHz). There have been a number of proposals to set up a second US
transmitter. The last time I noticed them beating the drum for one, it was 
going to be at 40 KHz rather than 60 KHz. The proposal pretty much died 
yet again ….

Since MSF *is* on 60 KHz, you do indeed get dead spots. There probably is an
interesting plot of locations that have issues with both the 40 KHz and 60 KHz
transmissions due to simply being in the wrong place. 

Bob

> 
> I tried to model this many years ago, but I don't trust the result,
> somebody with better HF-propagation chops than me should look at it.
> 
> In addition to that problem, switch-mode designers seems to just
> *love* 60 kHz, and at least here in Denmark there is a lot more
> "hash" around 60 kHz than 77.5 kHz.
> 
> Finally, the modulation scheme of MSF is a bit on the overengineered
> side, which makes pulse discrimination needlessly hard - as you have
> also found out.
> 
> The big advantage of the blame algorithm is that since it is so
> tolerant of missing pulses, you can be throw everything away which
> isn't 100% clearcut.
> 
> If you look at the top of the dcf77.c file, you can see how I did
> that for DCF77, but the complex modulation of MSF needs a much
> more complex state engine there.
> 
> Finally, many of the small "clock-receivers", like the one you use,
> are optimised for battery-life and therefore they use very resonant
> filters, often crystal-filters, and heavy low-pass after demodulation,
> and that trows away a LOT of information which would be useful to
> have to discriminate the pulses.
> 
> If you go for the SDR approach, you will have much more information
> available, and can use much more well-behaved filters to detect the
> pulses, and one added advantage of carrier-tracking is that the
> power-modulation is carrier-synchronous, which makes them much
> easier to spot.
> 
> So really:  Get yourself an 1MSPS ADC chip and go that route instead.
> 
> (In theory, certain modern sound-cards should be usable for this if
> you can rip out their low-pass filters.  Havn't tried.)
> 
> -- 
> 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] Symmetricom 58532A GPS Antenna : Launch3 Surplus

[Angus via time-nuts]

On Tue, 6 Feb 2018 14:54:23 -0500, you wrote:

>3) it’s designed for continuous outdoor use  (connector is well shielded etc)

That's something that has always baffled me - the number of antennas
which the manufacturers claim are suitable for long term outdoor use
that have connectors which are impossible to seal without large
quantities of sealant or whatever.

Angus.
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[paul swed]

Deirdre,
Great discussion on my favorite topic. I am the guy on the other side of
the lake that curses MSFs interference with WWVB.
I did indeed cheat by using the GPS time and 1 second tick to recreate the
WWVB timecode bits to remove the psk shifts in the received signal here on
the east coast. This allowed phase tracking receivers to correctly work
again.
Did MSF finally go to a BPSK signal format? I heard they were considering
that.
regards
Paul
WB8TSL

On Tue, Feb 6, 2018 at 4:26 PM, Poul-Henning Kamp 
wrote:

> 
> In message , Bob kb8tq
> writes:
>
> >If you want to get even more “nutty", look at the “seed” that you likely
> already have
> >for the computation. In this day and age, you probably know what day /
> month / year it is.
>
> So, some of us think of that as cheating :-)
>
> >Since you might not (say) know the hour, you have a +/- 1 day sort of
> tolerance on that. It rolls
> >into month and year in some cases. The seed adds complexity, but probably
> makes
> >things more robust.
>
> I tried it, and it gave surprisingly little benefit.
>
> Unless very fast initial aquisition is your goal (why?!) you get a
> more robust result by not "cheating", since in real life at some
> point your RTC chip will contain bogus values.
>
> If you go the SDR route and decode DCF77 and MSF (and 162kHz France,
> WWV/B, the japanese signal at 40kHz and the russian at 200/3 kHz for
> that matter) in parallel, it is perfectly fair to expect them all
> to have the same date (modulus timezones).
>
> And yes, I would really *love* to se a colaborative project that
> produced an "all-world VLF timecode SDR-receiver"...
>
> >One cute thing is that this stuff is (in general) not very compute
> intensive. If data past the
> >minute tick is being looked at, you probably can afford to run multiple
> parallel solutions (even
> >on a < $5 MCU).
>
> The NTPns ran on a Soekris4501 and I was never able to measure a
> difference in power having the DCF77 blame code running or not.
>
> After all, it's only sixty trival patterns to match once a second...
>
> --
> 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] Receiving the MSF time signal on cheap radio modules

[Poul-Henning Kamp]

In message , Bob kb8tq writes:

>If you want to get even more “nutty", look at the “seed” that you likely 
>already have 
>for the computation. In this day and age, you probably know what day / month / 
>year it is. 

So, some of us think of that as cheating :-)

>Since you might not (say) know the hour, you have a +/- 1 day sort of 
>tolerance on that. It rolls 
>into month and year in some cases. The seed adds complexity, but probably makes
>things more robust. 

I tried it, and it gave surprisingly little benefit.

Unless very fast initial aquisition is your goal (why?!) you get a
more robust result by not "cheating", since in real life at some
point your RTC chip will contain bogus values.

If you go the SDR route and decode DCF77 and MSF (and 162kHz France,
WWV/B, the japanese signal at 40kHz and the russian at 200/3 kHz for
that matter) in parallel, it is perfectly fair to expect them all
to have the same date (modulus timezones).

And yes, I would really *love* to se a colaborative project that
produced an "all-world VLF timecode SDR-receiver"...

>One cute thing is that this stuff is (in general) not very compute intensive. 
>If data past the 
>minute tick is being looked at, you probably can afford to run multiple 
>parallel solutions (even 
>on a < $5 MCU). 

The NTPns ran on a Soekris4501 and I was never able to measure a
difference in power having the DCF77 blame code running or not.

After all, it's only sixty trival patterns to match once a second...

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Poul-Henning Kamp]

In message 
, "Deirdre 
O'Byrne" writes:

>With a blame algorithm in place it should be possible to recover these signals.

Yes, easily.

At distance MSF is significantly harder to receive than DCF77.

One of the reasons is that USA also operates two 60kHz transmitters
also very precisely on frequency, so there are areas of the world
where the three signals cancel and areas where they reinforce
each other.

I tried to model this many years ago, but I don't trust the result,
somebody with better HF-propagation chops than me should look at it.

In addition to that problem, switch-mode designers seems to just
*love* 60 kHz, and at least here in Denmark there is a lot more
"hash" around 60 kHz than 77.5 kHz.

Finally, the modulation scheme of MSF is a bit on the overengineered
side, which makes pulse discrimination needlessly hard - as you have
also found out.

The big advantage of the blame algorithm is that since it is so
tolerant of missing pulses, you can be throw everything away which
isn't 100% clearcut.

If you look at the top of the dcf77.c file, you can see how I did
that for DCF77, but the complex modulation of MSF needs a much
more complex state engine there.

Finally, many of the small "clock-receivers", like the one you use,
are optimised for battery-life and therefore they use very resonant
filters, often crystal-filters, and heavy low-pass after demodulation,
and that trows away a LOT of information which would be useful to
have to discriminate the pulses.

If you go for the SDR approach, you will have much more information
available, and can use much more well-behaved filters to detect the
pulses, and one added advantage of carrier-tracking is that the
power-modulation is carrier-synchronous, which makes them much
easier to spot.

So really:  Get yourself an 1MSPS ADC chip and go that route instead.

(In theory, certain modern sound-cards should be usable for this if
you can rip out their low-pass filters.  Havn't tried.)

-- 
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] Anyone have experience with this antenna?

[Bob kb8tq]

Hi

Since we are talking about an L1 / L2 antenna here, a reasonable assumption 
would be that the target is something better than an “average result”. If you 
construct 
a cover out of a piece of PVC pipe (as shown in the original drawing), your 
worst 
case path has a foot or so of PVC in it compared to a best case path with well 
under
a tenth of an inch. That’s going to give you a bit of variation ….. Add some 
dirt or water
or ice to the equation and who knows what the result might be. 

Bob

> On Feb 6, 2018, at 3:45 PM, Michael Wouters  wrote:
> 
> I can see why the geodetic community would worry about antenna phase centre
> variation when a radome is installed but is it really an issue in timing
> applications? The few papers I've read suggest PCVs of less than 10 mm, or
> equivalently, 30 ps. This is at the level of precision available from
> post-processed, carrier phase time-transfer but  invisible in the 1 pps
> coming out of your receiver, even with a good sawtooth correction. Am I
> missing something?
> 
> Cheers
> Michael
> 
> On Wed, 7 Feb 2018 at 4:14 am, Bob kb8tq  wrote:
> 
>> Hi
>> 
>> There are “cell site” specific GPS antennas on the market. Panasonic has
>> had one out
>> for quite a while. I’m sure there are several others.
>> 
>> One issue with doing any sort of “cover” for a precision antenna is
>> distorting it’s pattern.
>> Plastic (or whatever you use) will have different properties than air. A
>> path through a blob
>> of “not air” will change the effective path length. That impacts the
>> timing and thus the
>> navigation solution. If you are worried about 2mm sort of pattern
>> accuracy, things get
>> tricky. Early on, there was a big “throw out the radomes push when this
>> was first noticed.
>> 
>> Bob
>> 
>>> On Feb 6, 2018, at 6:15 AM, Bo Hansen  wrote:
>>> 
>>> Hi
>>> 
>>> Besides the RF characteristics it may also be worth considering the
>> quality of the plastics used. Over time water ingress may become an issue.
>> Fours years after the installation of a CN brand antenna, sourced locally
>> so probably not counterfeit either, we had to replace it at OZ7IGY
>> www.oz7igy.dk
>>> 
>>> RF wise 42 dB of gain IS an issue. Again at OZ7IGY, with 12 carriers in
>> the air especially 13 cm and 23 cm, blocking and IMD were an issue before
>> we mounted a BPF. I have taken apart the above mentioned antenna, a
>> Motorola antenna and an eBay "hockey puck" antenna. The best design was
>> clearly the Motorola one because it had a BPF after the pre-amp - probably
>> because it was designed by RF competent people too. Each of the other ones
>> had two FETs/MMICs in series and then a BPF. Of cause if no nearby carriers
>> are in the air it may be less of an issue.
>>> 
>>> So designing a really good antenna and pre-amp may be a business
>> opportunity. There are many hi IP3 MMICs available designed for GPS and the
>> like purposes. SAW BPFs with <1 dB loss are available fairly cheap so one
>> before the FET/MMIC with a 1 dB NF is the way to go. A DIY radome using
>> standard materials from any hardware shop is attached.
>>> 
>>> Bo, OZ2M
>>> 
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Re: [time-nuts] eBay GPS antenna.

[Attila Kinali]

On Tue, 6 Feb 2018 07:08:42 -0600
John Green  wrote:

> Thanks for the responses. It looks similar to but not exactly like the two
> antennas referenced. They say the preamp is 3 to 5.5 volts, whereas the
> eBay antenna says its preamp is good from 3.3 to 18 volts, indicating I can
> run it off 12 volts.

I am pretty sure that this is either a mistake or a deliberate
deceit. Most LNA's I am aware of work between 3.3V and 5V. The
cheap ones are definitely all in that range. Some of those might
work for a short time with higher voltage, depending on the actual
semiconductor process used for production. But that means using
those chips outside their specs and putting a high straign on the
semiconductor, which will lead to an early death. It also cannot
be an LDO inside the antenna, as 3.3V is pretty much the lowest
voltage you can get an LNA for. There are some that work at 3.0V
still, but that would leave only 0.3V for the LDO, which requires
a more expensive LDO. I am pretty sure there are some LNAs that work
at 2.5V or even lower, but those would be definitely in the
way-too-expensive category.

So, my guess is, they tested the antenna whether it works with 12V,
seen that it does, and just "adjusted" the specs. But in reality,
the LNA still maxes out at 5V if you want a reliable device.


Attila Kinali
-- 
The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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Re: [time-nuts] Anyone have experience with this antenna?

[Michael Wouters]

I can see why the geodetic community would worry about antenna phase centre
variation when a radome is installed but is it really an issue in timing
applications? The few papers I've read suggest PCVs of less than 10 mm, or
equivalently, 30 ps. This is at the level of precision available from
post-processed, carrier phase time-transfer but  invisible in the 1 pps
coming out of your receiver, even with a good sawtooth correction. Am I
missing something?

Cheers
Michael

On Wed, 7 Feb 2018 at 4:14 am, Bob kb8tq  wrote:

> Hi
>
> There are “cell site” specific GPS antennas on the market. Panasonic has
> had one out
> for quite a while. I’m sure there are several others.
>
> One issue with doing any sort of “cover” for a precision antenna is
> distorting it’s pattern.
> Plastic (or whatever you use) will have different properties than air. A
> path through a blob
> of “not air” will change the effective path length. That impacts the
> timing and thus the
> navigation solution. If you are worried about 2mm sort of pattern
> accuracy, things get
> tricky. Early on, there was a big “throw out the radomes push when this
> was first noticed.
>
> Bob
>
> > On Feb 6, 2018, at 6:15 AM, Bo Hansen  wrote:
> >
> > Hi
> >
> > Besides the RF characteristics it may also be worth considering the
> quality of the plastics used. Over time water ingress may become an issue.
> Fours years after the installation of a CN brand antenna, sourced locally
> so probably not counterfeit either, we had to replace it at OZ7IGY
> www.oz7igy.dk
> >
> > RF wise 42 dB of gain IS an issue. Again at OZ7IGY, with 12 carriers in
> the air especially 13 cm and 23 cm, blocking and IMD were an issue before
> we mounted a BPF. I have taken apart the above mentioned antenna, a
> Motorola antenna and an eBay "hockey puck" antenna. The best design was
> clearly the Motorola one because it had a BPF after the pre-amp - probably
> because it was designed by RF competent people too. Each of the other ones
> had two FETs/MMICs in series and then a BPF. Of cause if no nearby carriers
> are in the air it may be less of an issue.
> >
> > So designing a really good antenna and pre-amp may be a business
> opportunity. There are many hi IP3 MMICs available designed for GPS and the
> like purposes. SAW BPFs with <1 dB loss are available fairly cheap so one
> before the FET/MMIC with a 1 dB NF is the way to go. A DIY radome using
> standard materials from any hardware shop is attached.
> >
> > Bo, OZ2M
> >
> > ___
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Bob kb8tq]

Hi

If you want to get even more “nutty", look at the “seed” that you likely 
already have 
for the computation. In this day and age, you probably know what day / month / 
year it is. 
Since you might not (say) know the hour, you have a +/- 1 day sort of tolerance 
on that. It rolls 
into month and year in some cases. The seed adds complexity, but probably makes
things more robust. 

If the purpose is to “always be right” then retaining a seed probably improves 
things. 

The flip side is (of course) “what if I’ve been lied to?”. That applies with or 
without a seed. 
Heading off into a situation where you never (re)lock could be one result. How 
long do you go before 
you decide to try something else? 

One cute thing is that this stuff is (in general) not very compute intensive. 
If data past the 
minute tick is being looked at, you probably can afford to run multiple 
parallel solutions (even 
on a < $5 MCU). 

Lots of zigs and zags ….

Bob

> On Feb 6, 2018, at 2:37 PM, Poul-Henning Kamp  wrote:
> 
> 
> In message 
> 
> , "Deirdre O'Byrne" writes:
> 
>> I've been trying to see if I could design a decoding algorithm that
>> would be more noise-tolerant than the algorithms I've seen out in
>> the wild.
> 
> You can: I baptised it "the blame algoritm".
> 
> The trick is not to try to accept pulses as valid but to try to
> throw out pulses which are impossible.
> 
> Imagine you have a 120 second long shift-register, and you feed
> your received pulses into it.
> 
> Then try brute force, for every one of the newest 60 positions if
> that can be the start of a minute or not, by testing all the
> constraints you can think of, and there are surprisingly many.
> 
> Some are obvious, the bits encoding the hour cannot contain "39",
> but that is a remarkable weak filter that seldom kicks in.
> 
> A much stronger filter is that the bits encoding the hour must be
> the same as in the previous minute *unless* minutes were 59 in the
> previous minute *and* zero in this minute.
> 
> If you count it up, that is a strong and very peculiar relationship
> on all the hour-bits and all the minutes-bits and if even one single
> of them are wrong, you can definitively discard that theory for the
> start of the minute.
> 
> A similar thing holds for the date bits, the time in the
> previous minute must be 23:59:59 and in this 00:00:00 for
> there to be any difference between the dates, and even
> then, only a small number of possible changes in the date
> bits are valid.
> 
> If you look in http://phk.freebsd.dk/phkrel/NTPns.20080902.tgz
> you will find a file called dcf77_blame.c with my code,
> here is a couple of the simpler tests:
> 
>/* LSB of minutes must be different from previous minute */
>j = ip->shiftprev[(offset + 21) % 60];
>if (j * ip->shiftreg[(offset + 21) % 60] > 0)
>FAIL((why, " 0"));
> 
>/*
> * If the LSB of minutes was '1' in previous minute
> * the next higher bit must have changed, if it was
> * a '0' it must not.
> */
>if (j *
>ip->shiftreg[(offset + 22) % 60] *
>ip->shiftprev[(offset + 22) % 60] > 0)
>FAIL((why, " 1"));
> 
> When using this algorithm, missing pulses is almost a
> non-issue up to around 40% of them missing, and even
> in an enviroment like that, it is not uncommon to see
> the algorithm lock on to the minute in about 34 seconds
> and know the full time in less than 3 minutes.
> 
> If you make your pulse width discriminator *really* selective,
> which you might as well, you can "blacklist" disproved
> minute positions for the next many minutes as the
> risk of a '1' and '0' being confused is close to zero.
> 
> That will get you minute lock, even with 70%-90% missing
> pulses, in a matter of minutes if you use a longer
> shift register.
> 
> I did a parallel prototype for MSF, but I didn't need it
> so I never completed it, not sure I have it around any
> more.
> 
> I should really write an article about that code...
> 
> Poul-Henning
> 
> -- 
> 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] Receiving the MSF time signal on cheap radio modules

[Deirdre O'Byrne]

That's the next level of error detection. Unfortunately I notice with MSF
and these cheap receivers it can be difficult to determine what the binary
values being transmitted during the second were, which was my motivation
for the analysis I did.

I notice that there is one significant difference between DCF and MSF - the
former does not entirely turn off the carrier during the second, whereas
the latter does. I suspect that is the reason why with MSF receivers it can
so often be difficult to determine what the binary values transmitted were,
as the receiver AGC circuitry possibly has a difficult time keeping up with
drastically changing received power levels, which subsequently give rise to
noise in the received signal.

Splitting the MSF received signal into 100ms chunks, all of the seconds
apart from the start-of-minute marker are of the form 0AB1. Using "x"
to represent a 100ms chunk whose value could not be determined, I notice
that many of the received seconds were of the form "0AB1x111" or "0AB11x11"
etc - i.e. there was only one 100ms chunk within the second whose value
could not be reliably determined and whose value was non-critical. With a
blame algorithm in place it should be possible to recover these signals.


On 6 February 2018 at 19:37, Poul-Henning Kamp  wrote:

> 
> In message  gmail.com>
> , "Deirdre O'Byrne" writes:
>
> >I've been trying to see if I could design a decoding algorithm that
> >would be more noise-tolerant than the algorithms I've seen out in
> >the wild.
>
> You can: I baptised it "the blame algoritm".
>
> The trick is not to try to accept pulses as valid but to try to
> throw out pulses which are impossible.
>
> Imagine you have a 120 second long shift-register, and you feed
> your received pulses into it.
>
> Then try brute force, for every one of the newest 60 positions if
> that can be the start of a minute or not, by testing all the
> constraints you can think of, and there are surprisingly many.
>
> Some are obvious, the bits encoding the hour cannot contain "39",
> but that is a remarkable weak filter that seldom kicks in.
>
> A much stronger filter is that the bits encoding the hour must be
> the same as in the previous minute *unless* minutes were 59 in the
> previous minute *and* zero in this minute.
>
> If you count it up, that is a strong and very peculiar relationship
> on all the hour-bits and all the minutes-bits and if even one single
> of them are wrong, you can definitively discard that theory for the
> start of the minute.
>
> A similar thing holds for the date bits, the time in the
> previous minute must be 23:59:59 and in this 00:00:00 for
> there to be any difference between the dates, and even
> then, only a small number of possible changes in the date
> bits are valid.
>
> If you look in http://phk.freebsd.dk/phkrel/NTPns.20080902.tgz
> you will find a file called dcf77_blame.c with my code,
> here is a couple of the simpler tests:
>
> /* LSB of minutes must be different from previous minute */
> j = ip->shiftprev[(offset + 21) % 60];
> if (j * ip->shiftreg[(offset + 21) % 60] > 0)
> FAIL((why, " 0"));
>
> /*
>  * If the LSB of minutes was '1' in previous minute
>  * the next higher bit must have changed, if it was
>  * a '0' it must not.
>  */
> if (j *
> ip->shiftreg[(offset + 22) % 60] *
> ip->shiftprev[(offset + 22) % 60] > 0)
> FAIL((why, " 1"));
>
> When using this algorithm, missing pulses is almost a
> non-issue up to around 40% of them missing, and even
> in an enviroment like that, it is not uncommon to see
> the algorithm lock on to the minute in about 34 seconds
> and know the full time in less than 3 minutes.
>
> If you make your pulse width discriminator *really* selective,
> which you might as well, you can "blacklist" disproved
> minute positions for the next many minutes as the
> risk of a '1' and '0' being confused is close to zero.
>
> That will get you minute lock, even with 70%-90% missing
> pulses, in a matter of minutes if you use a longer
> shift register.
>
> I did a parallel prototype for MSF, but I didn't need it
> so I never completed it, not sure I have it around any
> more.
>
> I should really write an article about that code...
>
> Poul-Henning
>
> --
> 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] Receiving the MSF time signal on cheap radio modules

[Poul-Henning Kamp]

In message 

Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Hal Murray]

rnabioul...@gmail.com said:
> How difficult would it be to complete these modules and integrate them with
> the rest of NTP, as NTP decoder modules?  So instead of an AM HF receiver,
> the setup for these signals would be: 

The simple way to do that is to use the shared-memory interface.  No changes 
to ntpd required.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] eBay GPS antenna.

[John Green]

It should work with a T bolt since its range is 3.3 to 18 volts. I also
have a good bias T and GPS type splitter that only passes power to one port
that I can also use. I hope the gain isn't a problem. I live in the
country, so local RF shouldn't be an issue. I can scrounge up some pads if
need be. I plan on starting out with the Leica if I can retrieve it from
its present location. Then, I will probably compare that to the Trimble and
later the Chinese made one. I also have a couple of the type they use at
cellsites, one of which is a Motorola. Something tells me that the Leica
will be the eventual winner. It is the only one that is a choke ring type.
I keep looking on eBay for a reasonably priced unit that will work with the
new L5 civilian band birds. Nothing so far.
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Deirdre O'Byrne]

I used this cheap (but good for the price!) signal analyser -

http://www.ebay.ie/itm/Hobby-Components-UK-USB-24M-8CH-24MHz-Logic-Analyser/161309221423?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I used sigrok to do the recording -

https://www.sigrok.org/

Let me know if you collect some data - I'd be interested in seeing your
results!


On 6 February 2018 at 19:36, Adrian Godwin  wrote:

> Hi Deirdre,
>
> I'd like to repeat your measurement at a different location (eastern
> england).
>
> What did you use to capture the data and write it as a vcd file ?
>
> -adrian
>
>
> On Tue, Feb 6, 2018 at 6:40 PM, Deirdre O'Byrne 
> wrote:
>
> > OK so it's not the microsecond or nanosecond stuff that much of this list
> > is about, but I've been running an experiment for the past few days
> > gathering data on how well (or otherwise) a pair of cheap EM2S radio
> > receiver modules receive the MSF radio signal. I've been trying to see
> if I
> > could design a decoding algorithm that would be more noise-tolerant than
> > the algorithms I've seen out in the wild.
> >
> > Details are on my github, and the results are presented in a paper -
> >
> > https://github.com/deirdreobyrne/MSF-EM2S/blob/master/paper.pdf
> > ___
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> >
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Ruslan Nabioullin]

On Tue, Feb 6, 2018 at 2:37 PM, Poul-Henning Kamp  wrote:
> If you look in http://phk.freebsd.dk/phkrel/NTPns.20080902.tgz
> you will find a file called dcf77_blame.c with my code,
> here is a couple of the simpler tests:
>
> /* LSB of minutes must be different from previous minute */
> j = ip->shiftprev[(offset + 21) % 60];
> if (j * ip->shiftreg[(offset + 21) % 60] > 0)
> FAIL((why, " 0"));
>
> /*
>  * If the LSB of minutes was '1' in previous minute
>  * the next higher bit must have changed, if it was
>  * a '0' it must not.
>  */
> if (j *
> ip->shiftreg[(offset + 22) % 60] *
> ip->shiftprev[(offset + 22) % 60] > 0)
> FAIL((why, " 1"));
> ...
> I did a parallel prototype for MSF, but I didn't need it
> so I never completed it, not sure I have it around any
> more.
>
> I should really write an article about that code...

How difficult would it be to complete these modules and integrate them
with the rest of NTP, as NTP decoder modules?  So instead of an AM HF
receiver, the setup for these signals would be:

LF receiver set to CW demodulation set to appropriate parameters ->
NTP timekeeping system sound card

One of my organization's projects consists of robust public time
transfer via NTP over the Internet, based on a combination of various
on-site standards (rackmount OCXO, rubidium, and/or cesium standards)
and external signals (incl. WWV and CHU, using preamplifier ->
preselector -> analog parametric demodulator -> sound card, controlled
by ionospheric prediction daemon software on GNU/Linux via GPIB), the
nodes being geographically dispersed throughout the US and Canada.
It's probable that I will end up relocating to Western Europe
(coincidentally, the Republic of Ireland!) in the moderate future, and
therefore it would be nice if these LF or HF signals were to be
supported, for use as fallbacks to the standard GNSS sources (each
site typically will have one military and one industrial civilian
rackmount GPS receiver).

-Ruslan

-- 
Ruslan Nabioullin
Wittgenstein Laboratories
rnabioul...@gmail.com
(508) 523-8535
50 Louise Dr.
Hollis, NH 03049
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Re: [time-nuts] Symmetricom 58532A GPS Antenna : Launch3 Surplus

[Bob kb8tq]

Hi

That’s likely a “better” antenna for a TBolt-only setup than the L1 / L2 gizmo 
that
we have been chatting about. Why? 

1) if it’s still $25 it would be ~ 1/4 the price

2) it has a pretty good filter built into it. 

3) it’s designed for continuous outdoor use  (connector is well shielded etc)

4) It’s smaller and easier to mount 

Lots to like.

Bob

> On Feb 6, 2018, at 2:45 PM, Gregory Beat  wrote:
> 
> https://www.febo.com/pipermail/time-nuts/2015-October/094105.html
> In 2014 and 2015 Launch3 Telecom offered NOS Symmetricom 58532A GPS Antennas 
> at a good price ($25 each) to time-nuts members  These were surplus (>750), 
> never used, due to mobile/cellular company merger over decade ago.  Looks 
> like they still have some.
> https://www.launch3telecom.com/symmetricom/58532a.html
> Symmetricom 58532A GPS Antenna -- Data-sheet
> http://www.microsemi.com/document-portal/doc_view/133381-58532a
> Launch3Telecom.com
> 27 Daniel Road
> Fairfield, New Jersey 07004
> ===
> 
> Sent from iPad Air
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[time-nuts] Symmetricom 58532A GPS Antenna : Launch3 Surplus

[Gregory Beat]

https://www.febo.com/pipermail/time-nuts/2015-October/094105.html
In 2014 and 2015 Launch3 Telecom offered NOS Symmetricom 58532A GPS Antennas at 
a good price ($25 each) to time-nuts members  These were surplus (>750), never 
used, due to mobile/cellular company merger over decade ago.  Looks like they 
still have some.
https://www.launch3telecom.com/symmetricom/58532a.html
Symmetricom 58532A GPS Antenna -- Data-sheet
http://www.microsemi.com/document-portal/doc_view/133381-58532a
Launch3Telecom.com
27 Daniel Road
Fairfield, New Jersey 07004
===

Sent from iPad Air
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Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Poul-Henning Kamp]

In message 
, "Deirdre O'Byrne" writes:

>I've been trying to see if I could design a decoding algorithm that
>would be more noise-tolerant than the algorithms I've seen out in
>the wild.

You can: I baptised it "the blame algoritm".

The trick is not to try to accept pulses as valid but to try to
throw out pulses which are impossible.

Imagine you have a 120 second long shift-register, and you feed
your received pulses into it.

Then try brute force, for every one of the newest 60 positions if
that can be the start of a minute or not, by testing all the
constraints you can think of, and there are surprisingly many.

Some are obvious, the bits encoding the hour cannot contain "39",
but that is a remarkable weak filter that seldom kicks in.

A much stronger filter is that the bits encoding the hour must be
the same as in the previous minute *unless* minutes were 59 in the
previous minute *and* zero in this minute.

If you count it up, that is a strong and very peculiar relationship
on all the hour-bits and all the minutes-bits and if even one single
of them are wrong, you can definitively discard that theory for the
start of the minute.

A similar thing holds for the date bits, the time in the
previous minute must be 23:59:59 and in this 00:00:00 for
there to be any difference between the dates, and even
then, only a small number of possible changes in the date
bits are valid.

If you look in http://phk.freebsd.dk/phkrel/NTPns.20080902.tgz
you will find a file called dcf77_blame.c with my code,
here is a couple of the simpler tests:

/* LSB of minutes must be different from previous minute */
j = ip->shiftprev[(offset + 21) % 60];
if (j * ip->shiftreg[(offset + 21) % 60] > 0)
FAIL((why, " 0"));

/*
 * If the LSB of minutes was '1' in previous minute
 * the next higher bit must have changed, if it was
 * a '0' it must not.
 */
if (j *
ip->shiftreg[(offset + 22) % 60] *
ip->shiftprev[(offset + 22) % 60] > 0)
FAIL((why, " 1"));

When using this algorithm, missing pulses is almost a
non-issue up to around 40% of them missing, and even
in an enviroment like that, it is not uncommon to see
the algorithm lock on to the minute in about 34 seconds
and know the full time in less than 3 minutes.

If you make your pulse width discriminator *really* selective,
which you might as well, you can "blacklist" disproved
minute positions for the next many minutes as the
risk of a '1' and '0' being confused is close to zero.

That will get you minute lock, even with 70%-90% missing
pulses, in a matter of minutes if you use a longer
shift register.

I did a parallel prototype for MSF, but I didn't need it
so I never completed it, not sure I have it around any
more.

I should really write an article about that code...

Poul-Henning

-- 
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] Receiving the MSF time signal on cheap radio modules

[Adrian Godwin]

Hi Deirdre,

I'd like to repeat your measurement at a different location (eastern
england).

What did you use to capture the data and write it as a vcd file ?

-adrian


On Tue, Feb 6, 2018 at 6:40 PM, Deirdre O'Byrne 
wrote:

> OK so it's not the microsecond or nanosecond stuff that much of this list
> is about, but I've been running an experiment for the past few days
> gathering data on how well (or otherwise) a pair of cheap EM2S radio
> receiver modules receive the MSF radio signal. I've been trying to see if I
> could design a decoding algorithm that would be more noise-tolerant than
> the algorithms I've seen out in the wild.
>
> Details are on my github, and the results are presented in a paper -
>
> https://github.com/deirdreobyrne/MSF-EM2S/blob/master/paper.pdf
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Re: [time-nuts] Anyone have experience with this antenna?

[Bo Hansen]

Hi

Indeed a radome may distort the antenna pattern. In teh case of DIY projects 
the trick that most can apply is to take a piece of the radome material and put 
it into a microwave own. If it doesn't get hot it is OK for most DIY cases.

Infinion have some nice GNSS MMICs e.g. BGA924N6 


Bo

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[time-nuts] Receiving the MSF time signal on cheap radio modules

[Deirdre O'Byrne]

OK so it's not the microsecond or nanosecond stuff that much of this list
is about, but I've been running an experiment for the past few days
gathering data on how well (or otherwise) a pair of cheap EM2S radio
receiver modules receive the MSF radio signal. I've been trying to see if I
could design a decoding algorithm that would be more noise-tolerant than
the algorithms I've seen out in the wild.

Details are on my github, and the results are presented in a paper -

https://github.com/deirdreobyrne/MSF-EM2S/blob/master/paper.pdf
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Re: [time-nuts] Anyone have experience with this antenna?

[Bob kb8tq]

Hi

The microwave trick is fine for working out if it is a lossy material. 
Unfortunately 
what gets you in this case is more than just loss. A coax cable has core 
material 
that will (usually) do quite well in a microwave. None the less, the delay 
through 
the coax is different than through air ( = the coax has a velocity factor). 

Bob


> On Feb 6, 2018, at 12:25 PM, Bo Hansen  wrote:
> 
> Hi
> 
> Indeed a radome may distort the antenna pattern. In teh case of DIY projects 
> the trick that most can apply is to take a piece of the radome material and 
> put it into a microwave own.  If it doesn't get hot it is OK for most DIY 
> cases.
> 
> Infinion have some nice GNSS MMICs e.g. BGA924N6 
> http://demo.21dianyuan.com/infineon/download/download_down/id/40/type/cn 
> 
> 
> Bo

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Re: [time-nuts] Anyone have experience with this antenna?

[Van Horn, David]

In a previous job, I used plastics to "lens" antennas at 2.4 GHz, shaping the 
patterns for more desirable results. 
XFDTD is a great software package for this application but it is expensive.
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Re: [time-nuts] Anyone have experience with this antenna?

[Bob kb8tq]

Hi

There are “cell site” specific GPS antennas on the market. Panasonic has had 
one out 
for quite a while. I’m sure there are several others. 

One issue with doing any sort of “cover” for a precision antenna is distorting 
it’s pattern. 
Plastic (or whatever you use) will have different properties than air. A path 
through a blob
of “not air” will change the effective path length. That impacts the timing and 
thus the 
navigation solution. If you are worried about 2mm sort of pattern accuracy, 
things get 
tricky. Early on, there was a big “throw out the radomes push when this was 
first noticed.

Bob

> On Feb 6, 2018, at 6:15 AM, Bo Hansen  wrote:
> 
> Hi
> 
> Besides the RF characteristics it may also be worth considering the quality 
> of the plastics used. Over time water ingress may become an issue. Fours 
> years after the installation of a CN brand antenna, sourced locally so 
> probably not counterfeit either, we had to replace it at OZ7IGY www.oz7igy.dk
> 
> RF wise 42 dB of gain IS an issue. Again at OZ7IGY, with 12 carriers in the 
> air especially 13 cm and 23 cm, blocking and IMD were an issue before we 
> mounted a BPF. I have taken apart the above mentioned antenna, a Motorola 
> antenna and an eBay "hockey puck" antenna. The best design was clearly the 
> Motorola one because it had a BPF after the pre-amp - probably because it was 
> designed by RF competent people too. Each of the other ones had two 
> FETs/MMICs in series and then a BPF. Of cause if no nearby carriers are in 
> the air it may be less of an issue.
> 
> So designing a really good antenna and pre-amp may be a business opportunity. 
> There are many hi IP3 MMICs available designed for GPS and the like purposes. 
> SAW BPFs with <1 dB loss are available fairly cheap so one before the 
> FET/MMIC with a 1 dB NF is the way to go. A DIY radome using standard 
> materials from any hardware shop is attached.
> 
> Bo, OZ2M
> 
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Re: [time-nuts] Heathkit GC 1000 Most Accurate Question

[Scott McGrath]

I've got one as well replaced that pot with 10 turn pot and electrolytic 
replacement

Content by Scott
Typos by Siri

On Feb 6, 2018, at 9:05 AM, paul swed  wrote:

Exactly they are the small open air pots.
Just one possibility along with the other good suggestions mentioned.
Regards
Paul
WB8TSL

On Tue, Feb 6, 2018 at 7:29 AM, Dave B via time-nuts 
wrote:

> 
>> Bill
>> I see the manual is online for the GC1000.
>> The 1KHZ tone decoder may be suspect in that its drifted off frequency.
> Its
>> a little ne-567 chip with a pot.
>> ne 567s were never all that great...
>> Regards
>> Paul
> 
> 
> 
> 567's are not too bad, not "precision", but not bad.
> 
> Small pot's are not great for long term stability either, especially if
> the track/wiper is exposed.
> 
> 73.
> 
> Dave.
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Re: [time-nuts] eBay GPS antenna.

[Bob kb8tq]

Hi

There is no need for something this exotic for L1 only reception. It *is*
nice to have Glonass L1, but that’s about the extent of how fancy you 
need to go. 

As noted in another post, the preamp gain probably is pretty high
on this antenna. That’s a standard that goes back to the early days of
Trimble survey GPS gear. It’s great if you happen to want to drive a 
32 port resistive splitter for your collection of GPSDO’s. If you have more
modest needs for splitting, pads would be a very good idea. 

Bob

> On Feb 6, 2018, at 8:08 AM, John Green  wrote:
> 
> Thanks for the responses. It looks similar to but not exactly like the two
> antennas referenced. They say the preamp is 3 to 5.5 volts, whereas the
> eBay antenna says its preamp is good from 3.3 to 18 volts, indicating I can
> run it off 12 volts. Regarding the internals, I must have somehow missed
> the photo which clearly shows it to be a patch antenna. It looks pretty
> similar to the Trimble I asked about recently, inside, that is. That
> Trimble had been dropped from a great height. The nylon screws that hold
> the actual antenna assembly had all been broken. I ordered new ones and
> replaced them. Disassembly was easy, reassembly not so much. Mine was made
> to have the groundplane, but doesn't have it. I suspect that since I am not
> doing surveying, it won't matter all that much. I bought an adapter for the
> 5/8 by 11 thread it uses and have a pvc pipe mount ready to go up. My
> location is not ideal. It will be atop a 40 foot Rohn 25 tower, but there
> are tall trees nearby. Since my Z3801 died, I don't have much of a GPSDO to
> use the antenna with. Just a couple of T bolts and some kind of postcard
> sized unit I need to build a housing and power supply for. Still, enough to
> experiment with.
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Re: [time-nuts] Heathkit GC 1000 Most Accurate Question

[paul swed]

Exactly they are the small open air pots.
Just one possibility along with the other good suggestions mentioned.
Regards
Paul
WB8TSL

On Tue, Feb 6, 2018 at 7:29 AM, Dave B via time-nuts 
wrote:

>
> > Bill
> > I see the manual is online for the GC1000.
> > The 1KHZ tone decoder may be suspect in that its drifted off frequency.
> Its
> > a little ne-567 chip with a pot.
> > ne 567s were never all that great...
> > Regards
> > Paul
>
> 
>
> 567's are not too bad, not "precision", but not bad.
>
> Small pot's are not great for long term stability either, especially if
> the track/wiper is exposed.
>
> 73.
>
> Dave.
> ___
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> mailman/listinfo/time-nuts
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>
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Re: [time-nuts] eBay GPS antenna.

[John Green]

Thanks for the responses. It looks similar to but not exactly like the two
antennas referenced. They say the preamp is 3 to 5.5 volts, whereas the
eBay antenna says its preamp is good from 3.3 to 18 volts, indicating I can
run it off 12 volts. Regarding the internals, I must have somehow missed
the photo which clearly shows it to be a patch antenna. It looks pretty
similar to the Trimble I asked about recently, inside, that is. That
Trimble had been dropped from a great height. The nylon screws that hold
the actual antenna assembly had all been broken. I ordered new ones and
replaced them. Disassembly was easy, reassembly not so much. Mine was made
to have the groundplane, but doesn't have it. I suspect that since I am not
doing surveying, it won't matter all that much. I bought an adapter for the
5/8 by 11 thread it uses and have a pvc pipe mount ready to go up. My
location is not ideal. It will be atop a 40 foot Rohn 25 tower, but there
are tall trees nearby. Since my Z3801 died, I don't have much of a GPSDO to
use the antenna with. Just a couple of T bolts and some kind of postcard
sized unit I need to build a housing and power supply for. Still, enough to
experiment with.
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[time-nuts] Anyone have experience with this antenna?

[Bo Hansen]

Hi

Besides the RF characteristics it may also be worth considering the quality of 
the plastics used. Over time water ingress may become an issue. Fours years 
after the installation of a CN brand antenna, sourced locally so probably not 
counterfeit either, we had to replace it at OZ7IGY www.oz7igy.dk

RF wise 42 dB of gain IS an issue. Again at OZ7IGY, with 12 carriers in the air 
especially 13 cm and 23 cm, blocking and IMD were an issue before we mounted a 
BPF. I have taken apart the above mentioned antenna, a Motorola antenna and an 
eBay "hockey puck" antenna. The best design was clearly the Motorola one 
because it had a BPF after the pre-amp - probably because it was designed by RF 
competent people too. Each of the other ones had two FETs/MMICs in series and 
then a BPF. Of cause if no nearby carriers are in the air it may be less of an 
issue.

So designing a really good antenna and pre-amp may be a business opportunity. 
There are many hi IP3 MMICs available designed for GPS and the like purposes. 
SAW BPFs with <1 dB loss are available fairly cheap so one before the FET/MMIC 
with a 1 dB NF is the way to go. A DIY radome using standard materials from any 
hardware shop is attached.

Bo, OZ2M

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Re: [time-nuts] Anyone have experience with this antenna?

[Attila Kinali]

On Tue, 6 Feb 2018 08:54:23 -0500
Bob kb8tq  wrote:

> One gotcha (if the data sheets are correct) is going to be the supply voltage.
> We normally stay away from 12V antennas because TBolt’s put out 5V. In the
> case of a survey antenna, 12V is what most of the gear puts out. I don’t know
> of any L1 / L2 gear that puts out 5 rather than 12V ….

Well, that's at least a very easy modification. Just open up the connection
between the bias-T and the LNA and insert some LM1117 or better an TPS7A45xx.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Anyone have experience with this antenna?

[Bob kb8tq]

Hi

One gotcha (if the data sheets are correct) is going to be the supply voltage.
We normally stay away from 12V antennas because TBolt’s put out 5V. In the
case of a survey antenna, 12V is what most of the gear puts out. I don’t know
of any L1 / L2 gear that puts out 5 rather than 12V ….

Bob

> On Feb 6, 2018, at 6:48 AM, Attila Kinali  wrote:
> 
> Moin,
> 
> On Mon, 5 Feb 2018 21:33:59 -0600
> John Green  wrote:
> 
>> https://www.ebay.com/itm/High-Precision-L1-L2-GNSS-GPS-GLONASS-BeiDou-RTK-CORS-survey-antenna/162718512935?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
>> 
>> Listed on eBay as a L1/L2 antenna with decent specs. They seem to indicate
>> it is as good as a choke ring antenna. I suspect it is just a patch in a
>> fancy package. 
> 
> It actually is. The fourth picture in the ebay listing shows that it's
> a dual, stacked patch antenna with a 4 point (0°, 90°, 180°, 270°)
> excitation using fiberglass as substrate. I am not sure I would trust
> the +/-2mm phase center error, but it's probably quite decent.
> But advertising it as "high precision" or even "chocke ring antenna
> functionality without out the size or weight" is an outright lie. 
> For one, they are too cheap to use nylon screws instead of
> metal screws in the antenna, which will lead to distortions in the
> radiation pattern. For another the fiberglass/epoxy substrate is going
> to change its dielectric constant with humidity, which will inevitably
> lead to changes in its resonance and radiation pattern. Third, the
> choke ring is to minimize influence of reflections close to or below
> the antenna horizon. This antenna does not have anything that comes even
> close to provide this feature.
> 
> Judging from the meager information on the ebay lsting, it's most likely
> a Shenzen Beitan 7151[1] or a 7201[2] ("data"sheets attached).
> 
> BTW: You can get the 7151 for 75USD and free sheeping on aliexpress.
> 
>> That is what the Leica and Trimble survey grade antennas I
>> have contain anyway. I bought one but haven't had the chance to do any
>> testing. I couldn't figure out how to get to the insides to take a peek
>> without damaging it. My antenna testing abilities are pretty feeble.
>> Mostly, I will just compare it to the Leica and Trimble to see how many
>> satellites it sees and look at position wander of the uBlox. Is there any
>> simple way to judge the quality of a GPS antenna?
> 
> If you have a known-good reference antenna and two receivers that can
> record the carrier phase data of the two antennas, then it's relatively
> easy to compare them (although there is quite a bit of math involved
> and you probably eed to write the software yourself, as i am not aware
> of any publicly, for hobbyists available software package).
> 
>   Attila Kinali
> 
> [1] http://www.sz-beitian.com/ProductsDetail?product_id=53
> [2] http://www.sz-beitian.com/ProductsDetail?product_id=52
> 
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] Heathkit GC 1000 Most Accurate Question

[Dave B via time-nuts]

> Bill
> I see the manual is online for the GC1000.
> The 1KHZ tone decoder may be suspect in that its drifted off frequency. Its
> a little ne-567 chip with a pot.
> ne 567s were never all that great...
> Regards
> Paul



567's are not too bad, not "precision", but not bad.

Small pot's are not great for long term stability either, especially if
the track/wiper is exposed.

73.

Dave.
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