Re: [time-nuts] PN/AM and 1.5Hz spur from frequency doubling?

[Bill Byrom]

Since the spur moved in frequency when the amplitude of the 25 MHz
interference changed, my guess is that you have some grounding or cable
leakage issues which are causing the measuring system to produce
erroneous results due to overloading. Do you have all instruments and
sources plugged into the same power line circuit with a common safety
ground? Have you tried moving the equipment cases close to each other
and connecting them with a large gauge wire or strap between the
chassis? A 2 M long RF cable is about a quarter wavelength at 25 MHz,
and it's easy to get ingress if the RF field is high, especially if you
aren't using double shielded cables. Also be sure the 25 MHz transmitter
and transmission line system is well shielded and properly grounded.


What type of cables and connectors are used in the signal path to the
phase noise analyzer?


Has someone performed a field intensity survey in conjunction with the
25 MHz transmitter for safety purposes? You may have a high RF field in
that area, and if the V/m is too great you will have many difficulties.


--

Bill Byrom N5BB







On Fri, Jan 20, 2017, at 01:21 PM, Bob Camp wrote:

> Hi

> 

> I would bet that the spur moving is an indicator of either the 25 MHz
> transmitter carrier or

> modulator drifting in frequency. My guess is that the Maser does not

> drift :)

> 

> Bob

> 

>> On Jan 20, 2017, at 12:22 PM, Anders Wallin
>>  wrote:
>> 

>> I made some progress with this issue today.

>> It turns I was using a 75Ohm cable at some point (doh!) which
>> caused a
>> 'forest' of spurs far out. Possibly our other maser has a
>> faulty/cut cable
>> which behaves similarly.

>> The final fix was to turn off our 25 MHz radio time-code
>> transmitter which
>> was causing the strong close-in spur at around 1.5 Hz. It uses a
>> modified
>> DCF77 code where it transmits full power AM-modulated 25MHz
>> carrier for 0,
>> 100ms or 200ms at the start of each second.

>> 

>> Here are PN plots of the 5MHz maser signal, same signal through 75ohm
>> reflective cable to the doubler, and through a 50ohm cable

>> to the doubler which solves the far-out spurs, and finally turning
>> off the
>> radio transmitter. The result is now close to the +6dBc/Hz
>> expected for a
>> doubler.

>> https://goo.gl/photos/qKKvg3SfE1XKxtq17

>> as a time-series of residual phase the switchoff of the time-code

>> transmitter looks like so:

>> https://goo.gl/photos/jNVJK2kj1kGUkSVd9

>> 

>> Finally I tried it with the transmitter on, but reduced coupling
>> into the
>> lab by disconnecting a few monitoring-cables. Strangely this
>> shifts the
>> spur even closer in (close to 1Hz now) and reduces the amplitude as
>> expected
>> https://goo.gl/photos/jG6rxfuC8R2QKchM6

>> 

>> What makes frequency doublers especially sensitive to this kind of

>> interference? The 25MHz carrier is phase-locked to better than 1e-
>> 12 to our
>> masers, so there can't reasonably be a 1-1.5Hz offset in the carrier
>> frequency. What is the interaction? (5th harmonic of 5Mhz mixes with
>> 25MHz?)
>> 

>> Anders

>> 

>> 

>> On Fri, Jan 20, 2017 at 11:06 AM, Anders Wallin
>> >> wrote:

>> 

>>> Thanks for all the comments so far.

>>> I will try the doubler with another quieter source, and try removing
>>> various potential noise-sources and exchanging cables...

>>> 

>>> I have now uploaded a few more images of the same data to the
>>> shared album
>>> linked in my earlier post.

>>> 

>>> Anders

>>> 

>>> On Thu, Jan 19, 2017 at 10:39 PM, Bill Byrom 
>>> wrote:
>>> 

 I see spurs at 50 Hz and harmonics, which I assume are from the
 power
 line at your location. This might be due to an oscillation in the
 power
 supply regulator, leading to nonlinear regulator operation and

 feedthrough of power line ripple. For example, low dropout
 regulators
 can sometimes oscillate when an additional ceramic bypass
 capacitor is
 added due to decreased phase margin in the feedback loop. It's also
 possible that there is too much ripple before the regulator and
 you are
 exceeding the dropout voltage, or that the regulator is going in
 and out
 of an overcurrent condition. Many odd things may happen if the
 power
 supply regular isn't working properly.

 

 

 --

 

 Bill Byrom N5BB

 

 

 

 

 

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Re: [time-nuts] PN/AM and 1.5Hz spur from frequency doubling?

[Bob Camp]

Hi

I would bet that the spur moving is an indicator of either the 25 MHz 
transmitter carrier or
modulator drifting in frequency. My guess is that the Maser does not drift :)

Bob

> On Jan 20, 2017, at 12:22 PM, Anders Wallin  
> wrote:
> 
> I made some progress with this issue today.
> It turns I was using a 75Ohm cable at some point (doh!) which caused a
> 'forest' of spurs far out. Possibly our other maser has a faulty/cut cable
> which behaves similarly.
> The final fix was to turn off our 25 MHz radio time-code transmitter which
> was causing the strong close-in spur at around 1.5 Hz. It uses a modified
> DCF77 code where it transmits full power AM-modulated 25MHz carrier for 0,
> 100ms or 200ms at the start of each second.
> 
> Here are PN plots of the 5MHz maser signal, same signal through 75ohm
> reflective cable to the doubler, and through a 50ohm cable
> to the doubler which solves the far-out spurs, and finally turning off the
> radio transmitter. The result is now close to the +6dBc/Hz expected for a
> doubler.
> https://goo.gl/photos/qKKvg3SfE1XKxtq17
> as a time-series of residual phase the switchoff of the time-code
> transmitter looks like so:
> https://goo.gl/photos/jNVJK2kj1kGUkSVd9
> 
> Finally I tried it with the transmitter on, but reduced coupling into the
> lab by disconnecting a few monitoring-cables. Strangely this shifts the
> spur even closer in (close to 1Hz now) and reduces the amplitude as expected
> https://goo.gl/photos/jG6rxfuC8R2QKchM6
> 
> What makes frequency doublers especially sensitive to this kind of
> interference? The 25MHz carrier is phase-locked to better than 1e-12 to our
> masers, so there can't reasonably be a 1-1.5Hz offset in the carrier
> frequency. What is the interaction? (5th harmonic of 5Mhz mixes with 25MHz?)
> 
> Anders
> 
> 
> On Fri, Jan 20, 2017 at 11:06 AM, Anders Wallin > wrote:
> 
>> Thanks for all the comments so far.
>> I will try the doubler with another quieter source, and try removing
>> various potential noise-sources and exchanging cables...
>> 
>> I have now uploaded a few more images of the same data to the shared album
>> linked in my earlier post.
>> 
>> Anders
>> 
>> On Thu, Jan 19, 2017 at 10:39 PM, Bill Byrom  wrote:
>> 
>>> I see spurs at 50 Hz and harmonics, which I assume are from the power
>>> line at your location. This might be due to an oscillation in the power
>>> supply regulator, leading to nonlinear regulator operation and
>>> feedthrough of power line ripple. For example, low dropout regulators
>>> can sometimes oscillate when an additional ceramic bypass capacitor is
>>> added due to decreased phase margin in the feedback loop. It's also
>>> possible that there is too much ripple before the regulator and you are
>>> exceeding the dropout voltage, or that the regulator is going in and out
>>> of an overcurrent condition. Many odd things may happen if the power
>>> supply regular isn't working properly.
>>> 
>>> 
>>> --
>>> 
>>> Bill Byrom N5BB
>>> 
>>> 
>>> 
>>> 
>>> 
 _
>>> 
 time-nuts mailing list -- time-nuts@febo.com
>>> 
 To unsubscribe, go to
>>> 
 https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> 
 and follow the instructions there.
>>> 
>>> 
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>>> ailman/listinfo/time-nuts
>>> and follow the instructions there.
>>> 
>> 
>> 
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Re: [time-nuts] PN/AM and 1.5Hz spur from frequency doubling?

[Anders Wallin]

I made some progress with this issue today.
It turns I was using a 75Ohm cable at some point (doh!) which caused a
'forest' of spurs far out. Possibly our other maser has a faulty/cut cable
which behaves similarly.
The final fix was to turn off our 25 MHz radio time-code transmitter which
was causing the strong close-in spur at around 1.5 Hz. It uses a modified
DCF77 code where it transmits full power AM-modulated 25MHz carrier for 0,
100ms or 200ms at the start of each second.

Here are PN plots of the 5MHz maser signal, same signal through 75ohm
reflective cable to the doubler, and through a 50ohm cable
 to the doubler which solves the far-out spurs, and finally turning off the
radio transmitter. The result is now close to the +6dBc/Hz expected for a
doubler.
https://goo.gl/photos/qKKvg3SfE1XKxtq17
as a time-series of residual phase the switchoff of the time-code
transmitter looks like so:
https://goo.gl/photos/jNVJK2kj1kGUkSVd9

Finally I tried it with the transmitter on, but reduced coupling into the
lab by disconnecting a few monitoring-cables. Strangely this shifts the
spur even closer in (close to 1Hz now) and reduces the amplitude as expected
https://goo.gl/photos/jG6rxfuC8R2QKchM6

What makes frequency doublers especially sensitive to this kind of
interference? The 25MHz carrier is phase-locked to better than 1e-12 to our
masers, so there can't reasonably be a 1-1.5Hz offset in the carrier
frequency. What is the interaction? (5th harmonic of 5Mhz mixes with 25MHz?)

Anders


On Fri, Jan 20, 2017 at 11:06 AM, Anders Wallin  wrote:

> Thanks for all the comments so far.
> I will try the doubler with another quieter source, and try removing
> various potential noise-sources and exchanging cables...
>
> I have now uploaded a few more images of the same data to the shared album
> linked in my earlier post.
>
> Anders
>
> On Thu, Jan 19, 2017 at 10:39 PM, Bill Byrom  wrote:
>
>> I see spurs at 50 Hz and harmonics, which I assume are from the power
>> line at your location. This might be due to an oscillation in the power
>> supply regulator, leading to nonlinear regulator operation and
>> feedthrough of power line ripple. For example, low dropout regulators
>> can sometimes oscillate when an additional ceramic bypass capacitor is
>> added due to decreased phase margin in the feedback loop. It's also
>> possible that there is too much ripple before the regulator and you are
>> exceeding the dropout voltage, or that the regulator is going in and out
>> of an overcurrent condition. Many odd things may happen if the power
>> supply regular isn't working properly.
>>
>>
>> --
>>
>> Bill Byrom N5BB
>>
>>
>>
>>
>>
>> > _
>>
>> > time-nuts mailing list -- time-nuts@febo.com
>>
>> > To unsubscribe, go to
>>
>> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>
>> > and follow the instructions there.
>>
>>
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>> ailman/listinfo/time-nuts
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>>
>
>
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Re: [time-nuts] PN/AM and 1.5Hz spur from frequency doubling?

[Anders Wallin]

Thanks for all the comments so far.
I will try the doubler with another quieter source, and try removing
various potential noise-sources and exchanging cables...

I have now uploaded a few more images of the same data to the shared album
linked in my earlier post.

Anders

On Thu, Jan 19, 2017 at 10:39 PM, Bill Byrom  wrote:

> I see spurs at 50 Hz and harmonics, which I assume are from the power
> line at your location. This might be due to an oscillation in the power
> supply regulator, leading to nonlinear regulator operation and
> feedthrough of power line ripple. For example, low dropout regulators
> can sometimes oscillate when an additional ceramic bypass capacitor is
> added due to decreased phase margin in the feedback loop. It's also
> possible that there is too much ripple before the regulator and you are
> exceeding the dropout voltage, or that the regulator is going in and out
> of an overcurrent condition. Many odd things may happen if the power
> supply regular isn't working properly.
>
>
> --
>
> Bill Byrom N5BB
>
>
>
>
>
> > _
>
> > time-nuts mailing list -- time-nuts@febo.com
>
> > To unsubscribe, go to
>
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>
> > and follow the instructions there.
>
>
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> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
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Re: [time-nuts] PN/AM and 1.5Hz spur from frequency doubling?

[Bill Byrom]

I see spurs at 50 Hz and harmonics, which I assume are from the power
line at your location. This might be due to an oscillation in the power
supply regulator, leading to nonlinear regulator operation and
feedthrough of power line ripple. For example, low dropout regulators
can sometimes oscillate when an additional ceramic bypass capacitor is
added due to decreased phase margin in the feedback loop. It's also
possible that there is too much ripple before the regulator and you are
exceeding the dropout voltage, or that the regulator is going in and out
of an overcurrent condition. Many odd things may happen if the power
supply regular isn't working properly.


--

Bill Byrom N5BB





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Re: [time-nuts] PN/AM and 1.5Hz spur from frequency doubling?

[John Miles]

You may find that the behavior varies quite a bit depending on what you put 
between the maser output and the doubler.  I've seen one case in particular 
that generates a ton of PM spurs, specifically an HP 11721A doubler driven by 
the 5 MHz output of a 5061A Cs standard.  The 5 MHz output uses a narrowband 
transformer with a parallel-tuned primary, so it looks highly reactive at 
frequencies other than 5 MHz.  I'm not sure what's really going on, but the 
11721A (which is being run below its frequency spec in this case) doesn't seem 
happy at all ( http://www.ke5fx.com/11721a.png ).  Adding an SLP-5 lowpass 
filter in front of the 11721A makes the spurs go away, as does an isolation amp.

The 1.5 Hz spur in your plot looks like leakage from a nearby 10 MHz source, 
presumably a free-running OCXO that's a bit off frequency.  The rest of it 
looks like an open coax shield or something.  (If you're using a coaxial balun, 
try removing it.)  It's possible to get 2-3 dB of excess noise from a 
multiplier beyond the expected 20*log(N), depending on source and load 
characteristics, but I haven't seen anything that bad in the absence of other 
problems.

-- john, KE5FX
Miles Design LLC

> >> I'm seeing +20-30 dBc/Hz of excess AM/PN, as well as a strong 1.5 Hz spur
> >> created by frequency doubling from 5 MHz to 10 MHz.
> >> https://goo.gl/photos/GFx9tQoxrSmyzUQo8
> >> The input amplitude to the doubler should be just above the
> recommended 11
> >> dBm.
> >> What's going on??
> >>
> >> thanks!
> >> Anders

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Re: [time-nuts] PN/AM and 1.5Hz spur from frequency doubling?

[Magnus Danielson]

Hi,

Considering that you have a diode and a tuned LC-tank, the tank will 
"ring" in it's own frequency, even if it is driven by the diode and 5 
MHz. This creates a single side-band tone which then shows up both as AM 
and PM. Well, that is my guess. 1.5 Hz is however very very close, which 
is quite impressive for 10 MHz, so there should be something more going 
on, I'm just speculating.


This gives some insight as one of many:
https://www.minicircuits.com/app/DOUB9-2.pdf
See the warning of over-power on last page.

MVH
Magnus

On 01/18/2017 06:01 PM, Bob Camp wrote:

Hi

Without seeing the circuit involved it’s a bit tough to guess all of the 
possible
things that might be happening. One branch leads off to things like the circuit
it’s self oscillating and creating the spur. Sub branches involve oscillation in
a regulator at low frequency vs RF oscillation somewhere else. Another branch
heads in the direction  of a loose cable running around the shop with a bunch
of 10 MHz on it. There are many branches ….

Bob


On Jan 18, 2017, at 11:13 AM, Anders Wallin  wrote:

I'm seeing +20-30 dBc/Hz of excess AM/PN, as well as a strong 1.5 Hz spur
created by frequency doubling from 5 MHz to 10 MHz.
https://goo.gl/photos/GFx9tQoxrSmyzUQo8
The input amplitude to the doubler should be just above the recommended 11
dBm.
What's going on??

thanks!
Anders
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Re: [time-nuts] PN/AM and 1.5Hz spur from frequency doubling?

[Bob Camp]

Hi

Without seeing the circuit involved it’s a bit tough to guess all of the 
possible
things that might be happening. One branch leads off to things like the circuit
it’s self oscillating and creating the spur. Sub branches involve oscillation 
in 
a regulator at low frequency vs RF oscillation somewhere else. Another branch 
heads in the direction  of a loose cable running around the shop with a bunch 
of 10 MHz on it. There are many branches ….

Bob

> On Jan 18, 2017, at 11:13 AM, Anders Wallin  
> wrote:
> 
> I'm seeing +20-30 dBc/Hz of excess AM/PN, as well as a strong 1.5 Hz spur
> created by frequency doubling from 5 MHz to 10 MHz.
> https://goo.gl/photos/GFx9tQoxrSmyzUQo8
> The input amplitude to the doubler should be just above the recommended 11
> dBm.
> What's going on??
> 
> thanks!
> Anders
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Re: [time-nuts] PN/AM and 1.5Hz spur from frequency doubling?

[Mattia Rizzi]

Hello,
can you share also the Phase Difference trace?

cheers,
Mattia

2017-01-18 17:13 GMT+01:00 Anders Wallin :

> I'm seeing +20-30 dBc/Hz of excess AM/PN, as well as a strong 1.5 Hz spur
> created by frequency doubling from 5 MHz to 10 MHz.
> https://goo.gl/photos/GFx9tQoxrSmyzUQo8
> The input amplitude to the doubler should be just above the recommended 11
> dBm.
> What's going on??
>
> thanks!
> Anders
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