[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[glenlist via time-nuts]

Super advice Ed, this is really really good advice.

Erik this is sage advice. especially CMR at high frequencies...

Oh and now LED lights overhead your bench which are driven at 5-50kHz 
are are next new coupling of noise into your open bench circuits !!!


Glen.

(RF engineer)

On 13/07/2022 7:09 am, ed breya via time-nuts wrote:
Erik, I'd really recommend that you use a real, "solid" ground 
reference on the instrumentation side, with +/- large (12-20 V) 
supplies, as others have suggested.


Your most recent setup diagram indicates that you're relying on the 
"differential" input of the audio PC card etc analyzer to allow for 
the "floating" common of the analysis circuit. Do you know what the 
common-mode rejection characteristics are? A true differential input 
would have two coax lines entering a symmetric differential to 
single-ended conversion stage at the front end. I doubt that the PC 
card actually has this, but maybe some form of DC/LF isolation from 
the local input common to chassis ground.


The PC likely has lots of SMPS noise in common-mode form, which 
probably can be ignored for audio (the SMPS frequencies are almost 
always quite far above audio). As long as the interference signals 
aren't too big to upset the LNA operation by say, rectification in 
various junctions (especially the front end), it should be OK. You 
will also have in-band line frequency and harmonics present in the 
common-mode signal, but these should be easier to deal with by virtue 
of whatever LF CMRR the sound card does have at lower frequencies.


Now consider the analysis circuit environment, where you have 
apparently zero intentional bypassing capacitance from the floating 
measurement common to chassis/earth ground. Here, the only bypass caps 
effectively are C1 at the REF buffer's input (which will only 
aggravate the situation), and the small capacitance between the ports 
of the mixers. I believe you have some bypassing at points in the 
other portion of the circuit - the PLL for the reference - but I don't 
know what that looks like now. So, just looking at this section, I'd 
say you need some serious bypassing to ground, for the RF signals from 
the mixers, and the common-mode signals in and out of the audio 
analyzer, DUT, and REF.


I recall there were some recent discussions about rail-splitting and 
such, but I didn't look closely. I thought surely someone would have 
mentioned the simple way to rail-split with an opamp, into a large 
capacitive load, but maybe not.


Without resorting to a more desirable ground-referenced, +/- supply 
scenario, you can add significant bypass capacitance from the signal 
common to ground, with slight change to the buffer circuit.


1. Add a resistor between the opamp's output and the load, which is 
signal common. The current demand appears small, so maybe around a 
couple to few hundred ohms should do.


2. Add a resistor in series with the (sense line) inverting input. 
This can be in the many k ohms range, depending the opamp's bias current.


3. Add a small capacitor between the opamp's output and inverting 
input to stabilize it.


4. Add the bypass cap.

This setup just isolates the opamp from the capacitive load, with the 
LF/DC regulated by the opamp, and the HF shunted by the bypass cap.


I'm guessing that once you get good bypassing here, the LNA will work 
much better, and you should see the difference with the lower noise 
opamp. The reason is that any opamp has limited CMRR, so improving the 
bypassing makes the "CM" part smaller. This is also another reason to 
operate opamp inputs at or near ground. Actually, the best CM 
improvement can be provided by running in inverting mode, so both 
inputs are always at ground. Non-inverting modes require the inputs to 
move, depending on the signal. In your LNA, the CM input signal range 
is not too bad, due to the high gain. The trick is to keep the overall 
CM - the operating common level wrt ground and the power supplies - 
constant and noise-free.


Regarding microphonics, since you mentioned tapping the housing, it 
sounds like you have "canned it up," which is a good thing. Assuming 
the REF and DUT are external, so not involved, the audible is coming 
from the analysis circuit only, right? That's not too surprising since 
it's a high gain system. It could be related to individual component 
microphonics, but I'd guess it's an RF effect. The whole thing is 
awash in the 2f signal and harmonics from the mixer, and to a lesser 
extent the DUT frequency signal that leaks through, so mechanical 
dimension changes or movements in the can, board, wiring etc, can 
change the EM pattern inside, giving tiny, noticeable phase shifts - 
after all, that's what it's for.


Ed


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[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)

[Bob kb8tq via time-nuts]

HI

We’re not building a synthesizer here. We are putting together
a simple piece of test gear. The purpose of the test gear is to 
measure phase noise down into the -170 dbc / Hz range …..

Bob

> On Jul 12, 2022, at 4:05 PM, Mike Monett via time-nuts 
>  wrote:
> 
> To Bob kb8tq:
> 
> Unfortunately, most of your post made very little sense. D-flops are noisy,
> and the higher you go in frequency, the noisier they are. This is clear
> from the schematic. Here is the schematic for a MC1670 D-flop: MC1670SC.PDF.
> 
> Most of the noise is generated in the input SR latch. When the clock signal
> arrives, the input latch state is transferred to the output SR latch.
> Obviously, the sheer number of transistors involved is going to generate
> noise.
> 
> Unfortunately, the D-flop is needed in every known synthesizer. Keeping
> this noise out of the signal is the goal of every designer. Stanford
> Research Systems is one company that has mastered the art. See
> 
> https://www.thinksrs.com/products/siggen.html
> 
> But you need to know how much noise is involved. That is where my new
> method can help. I am busy collecting parts - the HMC984LP4E's will arrive
> tomorrow, and I am looking for a pair of low noise VCXO's.
> 
> I will have to regenerate test equipment that I haven't used in 5 decades
> to measure deadband, loop bandwidth, damping, crosstalk, jitter response,
> etc. I will also get a DBM to compare the results.
> 
> I will also need ripple filters for the electronics. I have described this
> before in 2N3906G.PNG
> 
> All this will take time - maybe months. But I have intended on making my
> own phase noise analyzer for a long time, and this will be an excellent way
> to get started.
> 
> Along the way, there are plenty of other projects to attend to: a 4GHz to
> 8GHz low noise signal generator using YIG oscillators, a GPSDO to supply an
> accurate 10MHz reference, a new method of eliminating the sampling jitter
> in the 1PPS signal from the GPDSO, a low noise VCXO to supply a 10MHz
> reference from the 1PPS signal, an ultra stable signal generator to allow
> sampling of signals up to 150GHz, and so on.
> 
> As there is little else to talk about, I will go silent while I am working
> on these projects.
> 
> Bye
> 
> Mike
> <2N3906G.PNG>___
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[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[Lux, Jim via time-nuts]

On 7/12/22 3:51 PM, ed breya via time-nuts wrote:
I forgot to mention that you should also consider possible effects 
from the RF present, on the LNA. This can be more significant than 
SMPS frequencies getting where they don't belong, especially since the 
RF is intentionally right at the opamp's input. Your LPF only reduces, 
and does not eliminate, the 2F and harmonics, so there can be 
significant RF present on the LNA circuit.


A simplistic view is that the RF is far beyond the opamp's GBW or 
closed loop gain and should have no response, but it's not at all 
beyond upsetting or altering the operation. This can result in extra 
DC offsets and noise due to RF rectification in the input circuits, 
which only remain "linear" at frequencies where the output and 
feedback can keep up with the input.


This can be fixed if necessary, by adding extra RF filtering, 
particularly some built to low-pass at a higher cutoff frequency well 
above the analysis frequency, and well below the expected f and 2f.


For instance, in your circuit it looks like L1 is 1 mH, with 100 nF 
caps, which ideally cuts off quite low. However, 1 mH is a pretty big 
choke, and will tend to have a lot of inter-winding capacitance (and 
high resistance - don't forget to include it in noise), making it less 
effective at the higher frequencies. Adding an LC section in front of 
it, but set up for something in the MHz region, will give much greater 
rejection of the f and 2f, due to having more appropriate smaller L 
and C.


Anyway, if it works fine as is, then no problem, but it's something to 
be aware of if you get strange effects down the road.


Ed



and a single LC is only a single pole, so the roll off isn't all that 
great in a dB/decade sense.

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[time-nuts] DIY Low offset Phase Noise Analyzer (Erik Kaashoek)

[Mike Monett via time-nuts]

To Bob kb8tq:

Unfortunately, most of your post made very little sense. D-flops are noisy,
and the higher you go in frequency, the noisier they are. This is clear
from the schematic. Here is the schematic for a MC1670 D-flop: MC1670SC.PDF.

Most of the noise is generated in the input SR latch. When the clock signal
arrives, the input latch state is transferred to the output SR latch.
Obviously, the sheer number of transistors involved is going to generate
noise.

Unfortunately, the D-flop is needed in every known synthesizer. Keeping
this noise out of the signal is the goal of every designer. Stanford
Research Systems is one company that has mastered the art. See

https://www.thinksrs.com/products/siggen.html

But you need to know how much noise is involved. That is where my new
method can help. I am busy collecting parts - the HMC984LP4E's will arrive
tomorrow, and I am looking for a pair of low noise VCXO's.

I will have to regenerate test equipment that I haven't used in 5 decades
to measure deadband, loop bandwidth, damping, crosstalk, jitter response,
etc. I will also get a DBM to compare the results.

I will also need ripple filters for the electronics. I have described this
before in 2N3906G.PNG

All this will take time - maybe months. But I have intended on making my
own phase noise analyzer for a long time, and this will be an excellent way
to get started.

Along the way, there are plenty of other projects to attend to: a 4GHz to
8GHz low noise signal generator using YIG oscillators, a GPSDO to supply an
accurate 10MHz reference, a new method of eliminating the sampling jitter
in the 1PPS signal from the GPDSO, a low noise VCXO to supply a 10MHz
reference from the 1PPS signal, an ultra stable signal generator to allow
sampling of signals up to 150GHz, and so on.

As there is little else to talk about, I will go silent while I am working
on these projects.

Bye

Mike


MC1670SC.PDF
Description: Adobe PDF document
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[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[ed breya via time-nuts]

Erik, I'd really recommend that you use a real, "solid" ground reference 
on the instrumentation side, with +/- large (12-20 V) supplies, as 
others have suggested.


Your most recent setup diagram indicates that you're relying on the 
"differential" input of the audio PC card etc analyzer to allow for the 
"floating" common of the analysis circuit. Do you know what the 
common-mode rejection characteristics are? A true differential input 
would have two coax lines entering a symmetric differential to 
single-ended conversion stage at the front end. I doubt that the PC card 
actually has this, but maybe some form of DC/LF isolation from the local 
input common to chassis ground.


The PC likely has lots of SMPS noise in common-mode form, which probably 
can be ignored for audio (the SMPS frequencies are almost always quite 
far above audio). As long as the interference signals aren't too big to 
upset the LNA operation by say, rectification in various junctions 
(especially the front end), it should be OK. You will also have in-band 
line frequency and harmonics present in the common-mode signal, but 
these should be easier to deal with by virtue of whatever LF CMRR the 
sound card does have at lower frequencies.


Now consider the analysis circuit environment, where you have apparently 
zero intentional bypassing capacitance from the floating measurement 
common to chassis/earth ground. Here, the only bypass caps effectively 
are C1 at the REF buffer's input (which will only aggravate the 
situation), and the small capacitance between the ports of the mixers. I 
believe you have some bypassing at points in the other portion of the 
circuit - the PLL for the reference - but I don't know what that looks 
like now. So, just looking at this section, I'd say you need some 
serious bypassing to ground, for the RF signals from the mixers, and the 
common-mode signals in and out of the audio analyzer, DUT, and REF.


I recall there were some recent discussions about rail-splitting and 
such, but I didn't look closely. I thought surely someone would have 
mentioned the simple way to rail-split with an opamp, into a large 
capacitive load, but maybe not.


Without resorting to a more desirable ground-referenced, +/- supply 
scenario, you can add significant bypass capacitance from the signal 
common to ground, with slight change to the buffer circuit.


1. Add a resistor between the opamp's output and the load, which is 
signal common. The current demand appears small, so maybe around a 
couple to few hundred ohms should do.


2. Add a resistor in series with the (sense line) inverting input. This 
can be in the many k ohms range, depending the opamp's bias current.


3. Add a small capacitor between the opamp's output and inverting input 
to stabilize it.


4. Add the bypass cap.

This setup just isolates the opamp from the capacitive load, with the 
LF/DC regulated by the opamp, and the HF shunted by the bypass cap.


I'm guessing that once you get good bypassing here, the LNA will work 
much better, and you should see the difference with the lower noise 
opamp. The reason is that any opamp has limited CMRR, so improving the 
bypassing makes the "CM" part smaller. This is also another reason to 
operate opamp inputs at or near ground. Actually, the best CM 
improvement can be provided by running in inverting mode, so both inputs 
are always at ground. Non-inverting modes require the inputs to move, 
depending on the signal. In your LNA, the CM input signal range is not 
too bad, due to the high gain. The trick is to keep the overall CM - the 
operating common level wrt ground and the power supplies - constant and 
noise-free.


Regarding microphonics, since you mentioned tapping the housing, it 
sounds like you have "canned it up," which is a good thing. Assuming the 
REF and DUT are external, so not involved, the audible is coming from 
the analysis circuit only, right? That's not too surprising since it's a 
high gain system. It could be related to individual component 
microphonics, but I'd guess it's an RF effect. The whole thing is awash 
in the 2f signal and harmonics from the mixer, and to a lesser extent 
the DUT frequency signal that leaks through, so mechanical dimension 
changes or movements in the can, board, wiring etc, can change the EM 
pattern inside, giving tiny, noticeable phase shifts - after all, that's 
what it's for.


Ed



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[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[ed breya via time-nuts]

I forgot to mention that you should also consider possible effects from 
the RF present, on the LNA. This can be more significant than SMPS 
frequencies getting where they don't belong, especially since the RF is 
intentionally right at the opamp's input. Your LPF only reduces, and 
does not eliminate, the 2F and harmonics, so there can be significant RF 
present on the LNA circuit.


A simplistic view is that the RF is far beyond the opamp's GBW or closed 
loop gain and should have no response, but it's not at all beyond 
upsetting or altering the operation. This can result in extra DC offsets 
and noise due to RF rectification in the input circuits, which only 
remain "linear" at frequencies where the output and feedback can keep up 
with the input.


This can be fixed if necessary, by adding extra RF filtering, 
particularly some built to low-pass at a higher cutoff frequency well 
above the analysis frequency, and well below the expected f and 2f.


For instance, in your circuit it looks like L1 is 1 mH, with 100 nF 
caps, which ideally cuts off quite low. However, 1 mH is a pretty big 
choke, and will tend to have a lot of inter-winding capacitance (and 
high resistance - don't forget to include it in noise), making it less 
effective at the higher frequencies. Adding an LC section in front of 
it, but set up for something in the MHz region, will give much greater 
rejection of the f and 2f, due to having more appropriate smaller L and C.


Anyway, if it works fine as is, then no problem, but it's something to 
be aware of if you get strange effects down the road.


Ed



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[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[Stephen C. Menasian via time-nuts]

On Tue, 12 Jul 2022 08:17:33 -0800
Bob kb8tq via time-nuts  wrote:

> Hi
> 
> If you have any ceramic capacitors in the mix, they are often
> microphonic. The X7R versions are typically the best “high C” types.
> NPO’s normally are completely non-microphonic. Other non-ceramic caps
> should be ok, but who knows. 
> 
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Actually X7Rs are quite bad. Z5Us, also. Both are piezoelectric. I don't
use them any more except for power supply bypass in non-critical
supplies. As a part of a precision temperature controller project
(microKelvin), I needed to select capacitors for low microphonics.
The ceramic types mentioned above are the worst offenders; but
several other types (certain film types included) show some microphonic
activity.

Best to evaluate every capacitor type by charging to 10 Volts, or so, AC
coupling to an audio amplifier/sensitive oscilloscope/or other and tapping
to see if noise is produced.

Stephen Menasian
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[time-nuts] Re: GPS failed

[Mark Spencer via time-nuts]

Thanks Bob.

I believe this is what I have (I would need to climb up on the roof to double 
check the part number (assuming the label is still legible..))

https://www.microsemi.com/document-portal/doc_view/133381-58532a-datasheet

Best regards
Mark Spencer

Sent from Mail for Windows

From: Bob kb8tq
Sent: July 12, 2022 11:19 AM
To: Discussion of precise time and frequency 
measurement
Cc: Mark Spencer
Subject: Re: [time-nuts] GPS failed

Hi

The “typical” Symmetricom cone shaped GPS antennas are targeted at
cell phone tower applications. Being mounted on the same structure
as multiple cell transmitters puts them in a significant RF environment.
They have a *lot* of filtering built into the antenna to try to prevent overload
issues.

As with a lot of things, Symmetricom simply rebrands antennas made by
others. Not all cone shaped antennas are identical. However it’s a pretty
good bet that most of them are very similar to what Symmetericom ( and
the other folks ) supply for cell applications.

The “other end” of the range are the multi band saucer shaped “survey”
antennas. They tend to have a lot less filtering and be more focused at
allowing the user to access a wide range of frequencies ( both GNSS and
supplemental services) via a single device. Lots of filtering also tends to
mess up delay here or there, that’s not a great thing for high precision
work.

Bob

> On Jul 12, 2022, at 9:39 AM, Mark Spencer via time-nuts 
>  wrote:
>
> For what it is worth...
>
> I have a commercial grade ( Symmetricom ?) GPS antenna on the roof of my 
> home.  I don't recall ever having any issues with GPS reception despite 
> having / had various other transmit / receive antennas on the roof for 
> various frequencies from 1.8 MHz thru 1.3 GHz.  Power levels on some bands 
> (not including 1.2 GHz thru 1.3 GHz where I have never exceeded approx 10 
> watts) can equal or occasionally exceed 100 watts.
>
> As far as I know all my GPS receivers are using the typical 1.5 GHz GPS band.
>
> As usual the experiences of others may differ from mine.
>
> Best regards
> Mark Spencer
>
>> On Jul 12, 2022, at 12:08 AM, Matthias Welwarsky via time-nuts 
>>  wrote:
>>
>> Hi,
>>
>> if you're worried about in-band interference, the 23cm HAM radio band is
>> reasonably close to the L1 GPS frequency. When I was still active in packet
>> radio back in the days, our digipeater DB0DAR lost an interlink due to
>> interference with a precision GPS receiver in use by another university
>> institute. We had to shut it down. I think they operated a DGPS site at the
>> time and our link traffic caused errors in the correction data. Or something.
>>
>> BR,
>> Matthias
>>
>>> On Montag, 11. Juli 2022 01:19:18 CEST skipp Isaham via time-nuts wrote:
>>> Hello to the Group,
>>>
>>> I'd like to get some opinions and war stories regarding GPS reliability at
>>> high RF level and elevation locations.
>>>
>>> Background:  Three different hill-top GPS receivers, all different types,
>>> using different antennas mounted on an outside fixiture, plain view of the
>>> open sky, all stopped working.
>>>
>>> Test antennas were brought in and placed on a fixture well away from the
>>> original antennas, the recevers went back in to capture and lock.
>>>
>>> From what I understand, the original antennas are what I would call straight
>>> preamp with no pre-selection / filtering.
>>>
>>> The ordered and now inbound replacements are said to contain a SAW filter
>>> system. It is the intent of the client to just place these "improved
>>> antennas" in to service and get on with life.
>>>
>>> I would suspect a GPS antenna (and receiver) could be subject to RF overload
>>> or blocking, however, we're assuming nothing major has changed at the site,
>>> nor any nearby location.  One might think there are more GPS receivers
>>> being pushed out of reliable operation by the world around them, I'm just
>>> not hearing those stories from a lot of people using them (GPS receivers).
>>>
>>> Any new install GPS receiver antenna ordered will/should contain some
>>> pre-selection to potentially avoid a problem, even some years down the
>>> road? Seems like that's where things are going... no more off the shelf,
>>> wide band, (hot) preamplified GPS antennas in busy locations?
>>>
>>> Thank you in advance for any related comments and/or opions ...
>>>
>>> cheers,
>>>
>>> skipp
>>>
>>> skipp025 at jah who dot calm
>>> ___
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>>
>>
>>
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[time-nuts] Re: GPS failed

[Bob kb8tq via time-nuts]

Hi

The “typical” Symmetricom cone shaped GPS antennas are targeted at 
cell phone tower applications. Being mounted on the same structure
as multiple cell transmitters puts them in a significant RF environment. 
They have a *lot* of filtering built into the antenna to try to prevent overload
issues. 

As with a lot of things, Symmetricom simply rebrands antennas made by
others. Not all cone shaped antennas are identical. However it’s a pretty
good bet that most of them are very similar to what Symmetericom ( and
the other folks ) supply for cell applications. 

The “other end” of the range are the multi band saucer shaped “survey” 
antennas. They tend to have a lot less filtering and be more focused at 
allowing the user to access a wide range of frequencies ( both GNSS and
supplemental services) via a single device. Lots of filtering also tends to 
mess up delay here or there, that’s not a great thing for high precision 
work. 

Bob

> On Jul 12, 2022, at 9:39 AM, Mark Spencer via time-nuts 
>  wrote:
> 
> For what it is worth...
> 
> I have a commercial grade ( Symmetricom ?) GPS antenna on the roof of my 
> home.  I don't recall ever having any issues with GPS reception despite 
> having / had various other transmit / receive antennas on the roof for 
> various frequencies from 1.8 MHz thru 1.3 GHz.  Power levels on some bands 
> (not including 1.2 GHz thru 1.3 GHz where I have never exceeded approx 10 
> watts) can equal or occasionally exceed 100 watts.
> 
> As far as I know all my GPS receivers are using the typical 1.5 GHz GPS band.
> 
> As usual the experiences of others may differ from mine.
> 
> Best regards 
> Mark Spencer
> 
>> On Jul 12, 2022, at 12:08 AM, Matthias Welwarsky via time-nuts 
>>  wrote:
>> 
>> Hi,
>> 
>> if you're worried about in-band interference, the 23cm HAM radio band is 
>> reasonably close to the L1 GPS frequency. When I was still active in packet 
>> radio back in the days, our digipeater DB0DAR lost an interlink due to 
>> interference with a precision GPS receiver in use by another university 
>> institute. We had to shut it down. I think they operated a DGPS site at the 
>> time and our link traffic caused errors in the correction data. Or something.
>> 
>> BR,
>> Matthias
>> 
>>> On Montag, 11. Juli 2022 01:19:18 CEST skipp Isaham via time-nuts wrote:
>>> Hello to the Group,
>>> 
>>> I'd like to get some opinions and war stories regarding GPS reliability at
>>> high RF level and elevation locations.
>>> 
>>> Background:  Three different hill-top GPS receivers, all different types,
>>> using different antennas mounted on an outside fixiture, plain view of the
>>> open sky, all stopped working.
>>> 
>>> Test antennas were brought in and placed on a fixture well away from the
>>> original antennas, the recevers went back in to capture and lock.
>>> 
>>> From what I understand, the original antennas are what I would call straight
>>> preamp with no pre-selection / filtering.
>>> 
>>> The ordered and now inbound replacements are said to contain a SAW filter
>>> system. It is the intent of the client to just place these "improved
>>> antennas" in to service and get on with life.
>>> 
>>> I would suspect a GPS antenna (and receiver) could be subject to RF overload
>>> or blocking, however, we're assuming nothing major has changed at the site,
>>> nor any nearby location.  One might think there are more GPS receivers
>>> being pushed out of reliable operation by the world around them, I'm just
>>> not hearing those stories from a lot of people using them (GPS receivers).
>>> 
>>> Any new install GPS receiver antenna ordered will/should contain some
>>> pre-selection to potentially avoid a problem, even some years down the
>>> road? Seems like that's where things are going... no more off the shelf,
>>> wide band, (hot) preamplified GPS antennas in busy locations?
>>> 
>>> Thank you in advance for any related comments and/or opions ...
>>> 
>>> cheers,
>>> 
>>> skipp
>>> 
>>> skipp025 at jah who dot calm
>>> ___
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>> 
>> 
>> 
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[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[Lux, Jim via time-nuts]

On 7/12/22 8:53 AM, Erik Kaashoek via time-nuts wrote:

I'm struggling with the noise floor.
First tests where done with a 5nV/sqrt(Hz) opamp. Noise floor with 
shorted mixer output at 10kHz was -140dBc/Hz. Then I tried with 
1nV/sqrt(Hz) opamp, but that made no difference, noise floor at 10kHz 
was still -140dBc/Hz
The setup was simplified to this schematic: 
http://athome.kaashoek.com/time-nuts/PNA/SSPNA.JPG


What's the noise contribution of the resistors? V = sqrt(4*k*T*R*B)

51 ohms  is sqrt (4 * 1.38E-23 * 300 * 51) = 0.9 nV/sqrt(Hz)  100 ohms 
is ~1.4 nV/sqrt(Hz)


What kind of op amp? what's the current noise vs the voltage noise?  - 
you might low voltage noise, but high current noise, and that current 
noise across the input impedance can turn into surprisingly high voltage 
noise at the output.



The REF_buffer creates a virtual ground, the Audio_LNA amplifies into 
the differential audio output .

Why did the lower noise opamp not make a difference?
Also the setup is acting like a nice microphone. Tapping the housing 
is clearly audible. Which component may be causing the microphony?


My guess would be a parasitic capacitance between circuit and housing. 
changing the distance changes the C.





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[time-nuts] Re: GPS failed

[Mark Spencer via time-nuts]

For what it is worth...

 I have a commercial grade ( Symmetricom ?) GPS antenna on the roof of my home. 
 I don't recall ever having any issues with GPS reception despite having / had 
various other transmit / receive antennas on the roof for various frequencies 
from 1.8 MHz thru 1.3 GHz.  Power levels on some bands (not including 1.2 GHz 
thru 1.3 GHz where I have never exceeded approx 10 watts) can equal or 
occasionally exceed 100 watts.

As far as I know all my GPS receivers are using the typical 1.5 GHz GPS band.

As usual the experiences of others may differ from mine.

Best regards 
Mark Spencer

> On Jul 12, 2022, at 12:08 AM, Matthias Welwarsky via time-nuts 
>  wrote:
> 
> Hi,
> 
> if you're worried about in-band interference, the 23cm HAM radio band is 
> reasonably close to the L1 GPS frequency. When I was still active in packet 
> radio back in the days, our digipeater DB0DAR lost an interlink due to 
> interference with a precision GPS receiver in use by another university 
> institute. We had to shut it down. I think they operated a DGPS site at the 
> time and our link traffic caused errors in the correction data. Or something.
> 
> BR,
> Matthias
> 
>> On Montag, 11. Juli 2022 01:19:18 CEST skipp Isaham via time-nuts wrote:
>> Hello to the Group,
>> 
>> I'd like to get some opinions and war stories regarding GPS reliability at
>> high RF level and elevation locations.
>> 
>> Background:  Three different hill-top GPS receivers, all different types,
>> using different antennas mounted on an outside fixiture, plain view of the
>> open sky, all stopped working.
>> 
>> Test antennas were brought in and placed on a fixture well away from the
>> original antennas, the recevers went back in to capture and lock.
>> 
>> From what I understand, the original antennas are what I would call straight
>> preamp with no pre-selection / filtering.
>> 
>> The ordered and now inbound replacements are said to contain a SAW filter
>> system. It is the intent of the client to just place these "improved
>> antennas" in to service and get on with life.
>> 
>> I would suspect a GPS antenna (and receiver) could be subject to RF overload
>> or blocking, however, we're assuming nothing major has changed at the site,
>> nor any nearby location.  One might think there are more GPS receivers
>> being pushed out of reliable operation by the world around them, I'm just
>> not hearing those stories from a lot of people using them (GPS receivers).
>> 
>> Any new install GPS receiver antenna ordered will/should contain some
>> pre-selection to potentially avoid a problem, even some years down the
>> road? Seems like that's where things are going... no more off the shelf,
>> wide band, (hot) preamplified GPS antennas in busy locations?
>> 
>> Thank you in advance for any related comments and/or opions ...
>> 
>> cheers,
>> 
>> skipp
>> 
>> skipp025 at jah who dot calm
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> 
> 
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[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[Bob kb8tq via time-nuts]

Hi

If you have any ceramic capacitors in the mix, they are often microphonic. 
The X7R versions are typically the best “high C” types. NPO’s normally are
completely non-microphonic. Other non-ceramic caps should be ok, but 
who knows. 

Roughly speaking, 1 nV / Hz should be low enough to not matter. Since all
these specs are “typical” one never knows quite what this or that part may
be doing. You *should* see a drop putting in a 1 nV in place of a 5 nV.

Bob

> On Jul 12, 2022, at 7:53 AM, Erik Kaashoek  wrote:
> 
> I'm struggling with the noise floor.
> First tests where done with a 5nV/sqrt(Hz) opamp. Noise floor with shorted 
> mixer output at 10kHz was -140dBc/Hz. Then I tried with 1nV/sqrt(Hz) opamp, 
> but that made no difference, noise floor at 10kHz was still -140dBc/Hz
> The setup was simplified to this schematic: 
> http://athome.kaashoek.com/time-nuts/PNA/SSPNA.JPG
> The REF_buffer creates a virtual ground, the Audio_LNA amplifies into the 
> differential audio output .
> Why did the lower noise opamp not make a difference?
> Also the setup is acting like a nice microphone. Tapping the housing is 
> clearly audible. Which component may be causing the microphony?
> 
> 
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[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik, Kaashoek)

[Erik Kaashoek via time-nuts]

I'm struggling with the noise floor.
First tests where done with a 5nV/sqrt(Hz) opamp. Noise floor with 
shorted mixer output at 10kHz was -140dBc/Hz. Then I tried with 
1nV/sqrt(Hz) opamp, but that made no difference, noise floor at 10kHz 
was still -140dBc/Hz
The setup was simplified to this schematic: 
http://athome.kaashoek.com/time-nuts/PNA/SSPNA.JPG
The REF_buffer creates a virtual ground, the Audio_LNA amplifies into 
the differential audio output .

Why did the lower noise opamp not make a difference?
Also the setup is acting like a nice microphone. Tapping the housing is 
clearly audible. Which component may be causing the microphony?


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[time-nuts] Re: GPS failed

[John Sloan via time-nuts]

> I'd like to get some opinions and war stories regarding GPS reliability at 
> high RF level and elevation locations. 

At last count I’ve got ten GPS/GNSS active antennas scattered around the
house (I have a very understanding spousal unit), including one in the
kitchen skylight and one outside. We are currently in a sunspot cycle, and
this summer has been an unusually active season. Several times I’ve seen
one or more of my systems fail, sometimes for a couple of days at a time.

I subscribe to the NOAA Space Weather Prediction Center alert system.

https://www.swpc.noaa.gov/communities/space-weather-enthusiasts

Inevitably about the time I’m thinking about swapping an antenna to see if
it fixes the problem, I get an alert from the SWPC warning about a major
coronal mass ejection event.

I’ve finally learning to check the SWPC web site first before messing with
hardware. I’ve also learned to check the systems before sunrise (I’m an
early riser anyway) and after sunset.

In each case the systems effected came back to working order without my
having to do anything. Some antennas - regardless of location - seem to
be affected more than others.

(Why so many antennas? Five of them are GPS-disciplined NTP servers. Two
of them are part of a little NTP/GPS monitoring system I built. Two are
part of a Differential GNSS test bed I run 24x7. And one is just the test
antenna to my work bench for whatever I’m working on.)

- John

--
J. L. Sloan Digital Aggregates Corporation
+1.303.489.5178 3440 Youngfield Street
mailto:jsl...@diag.com  #209
http://www.diag.com Wheat Ridge CO 80033 USA




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[time-nuts] Re: GPS failed

[Björn via time-nuts]

Hi Matthias,

There has been interference reported and resolved between 23cm and Galileo, 
which have signals in the 23cm band. 

/Björn 

Sent from my Phone

> On 12 Jul 2022, at 09:20, Matthias Welwarsky via time-nuts 
>  wrote:
> 
> Hi,
> 
> if you're worried about in-band interference, the 23cm HAM radio band is 
> reasonably close to the L1 GPS frequency. When I was still active in packet 
> radio back in the days, our digipeater DB0DAR lost an interlink due to 
> interference with a precision GPS receiver in use by another university 
> institute. We had to shut it down. I think they operated a DGPS site at the 
> time and our link traffic caused errors in the correction data. Or something.
> 
> BR,
> Matthias
> 
>> On Montag, 11. Juli 2022 01:19:18 CEST skipp Isaham via time-nuts wrote:
>> Hello to the Group,
>> 
>> I'd like to get some opinions and war stories regarding GPS reliability at
>> high RF level and elevation locations.
>> 
>> Background:  Three different hill-top GPS receivers, all different types,
>> using different antennas mounted on an outside fixiture, plain view of the
>> open sky, all stopped working.
>> 
>> Test antennas were brought in and placed on a fixture well away from the
>> original antennas, the recevers went back in to capture and lock.
>> 
>> From what I understand, the original antennas are what I would call straight
>> preamp with no pre-selection / filtering.
>> 
>> The ordered and now inbound replacements are said to contain a SAW filter
>> system. It is the intent of the client to just place these "improved
>> antennas" in to service and get on with life.
>> 
>> I would suspect a GPS antenna (and receiver) could be subject to RF overload
>> or blocking, however, we're assuming nothing major has changed at the site,
>> nor any nearby location.  One might think there are more GPS receivers
>> being pushed out of reliable operation by the world around them, I'm just
>> not hearing those stories from a lot of people using them (GPS receivers).
>> 
>> Any new install GPS receiver antenna ordered will/should contain some
>> pre-selection to potentially avoid a problem, even some years down the
>> road? Seems like that's where things are going... no more off the shelf,
>> wide band, (hot) preamplified GPS antennas in busy locations?
>> 
>> Thank you in advance for any related comments and/or opions ...
>> 
>> cheers,
>> 
>> skipp
>> 
>> skipp025 at jah who dot calm
>> ___
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> 
> 
> 
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[time-nuts] Re: GPS failed

[Scott McGrath via time-nuts]

I’m going to bring up jamming here as 1) i live directly under a military air 
route.  2) a local OTR  trucker brings regularly scheduled jamming when he 
leaves/arrives home.

Your client could also be in proximity to a ‘prepper’ who is running a GPS 
jammer to prevent ‘three letter agencies’ from tracking them.   Or a trucker 
doing the same and forgetting to shut down their jammer.   GPS jammers are 
available ‘under the counter’ at virtually every truck stop in the US.

Yes it’s highly illegal and disrespectful of other system users and in the 
prepper case will eventually attract the attention of those very authorities 
they wished to avoid.

A reasonable way to check for jamming is the FAA ADS-B system.   if a ADS-B 
outage exists in same area and time as client sees GPS failure Client is likely 
to be experiencing jamming as ADS-B utilizes onboard GPS receivers to report 
aircraft position using a transmitter at   1090MHz in real time instead of 
depending on ATC radar to trigger a transponder.

Link to the FAA ADS-B outage system below 

https://sapt.faa.gov/outages.php?outageType=129001450=0.5





Content by Scott
Typos by Siri

On Jul 12, 2022, at 3:20 AM, Matthias Welwarsky via time-nuts 
 wrote:

Hi,

if you're worried about in-band interference, the 23cm HAM radio band is 
reasonably close to the L1 GPS frequency. When I was still active in packet 
radio back in the days, our digipeater DB0DAR lost an interlink due to 
interference with a precision GPS receiver in use by another university 
institute. We had to shut it down. I think they operated a DGPS site at the 
time and our link traffic caused errors in the correction data. Or something.

BR,
Matthias

On Montag, 11. Juli 2022 01:19:18 CEST skipp Isaham via time-nuts wrote:
> Hello to the Group,
> 
> I'd like to get some opinions and war stories regarding GPS reliability at
> high RF level and elevation locations.
> 
> Background:  Three different hill-top GPS receivers, all different types,
> using different antennas mounted on an outside fixiture, plain view of the
> open sky, all stopped working.
> 
> Test antennas were brought in and placed on a fixture well away from the
> original antennas, the recevers went back in to capture and lock.
> 
> From what I understand, the original antennas are what I would call straight
> preamp with no pre-selection / filtering.
> 
> The ordered and now inbound replacements are said to contain a SAW filter
> system. It is the intent of the client to just place these "improved
> antennas" in to service and get on with life.
> 
> I would suspect a GPS antenna (and receiver) could be subject to RF overload
> or blocking, however, we're assuming nothing major has changed at the site,
> nor any nearby location.  One might think there are more GPS receivers
> being pushed out of reliable operation by the world around them, I'm just
> not hearing those stories from a lot of people using them (GPS receivers).
> 
> Any new install GPS receiver antenna ordered will/should contain some
> pre-selection to potentially avoid a problem, even some years down the
> road? Seems like that's where things are going... no more off the shelf,
> wide band, (hot) preamplified GPS antennas in busy locations?
> 
> Thank you in advance for any related comments and/or opions ...
> 
> cheers,
> 
> skipp
> 
> skipp025 at jah who dot calm
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-le...@lists.febo.com



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[time-nuts] Re: GPS failed

[Matthias Welwarsky via time-nuts]

Hi,

if you're worried about in-band interference, the 23cm HAM radio band is 
reasonably close to the L1 GPS frequency. When I was still active in packet 
radio back in the days, our digipeater DB0DAR lost an interlink due to 
interference with a precision GPS receiver in use by another university 
institute. We had to shut it down. I think they operated a DGPS site at the 
time and our link traffic caused errors in the correction data. Or something.

BR,
Matthias

On Montag, 11. Juli 2022 01:19:18 CEST skipp Isaham via time-nuts wrote:
> Hello to the Group,
> 
> I'd like to get some opinions and war stories regarding GPS reliability at
> high RF level and elevation locations.
> 
> Background:  Three different hill-top GPS receivers, all different types,
> using different antennas mounted on an outside fixiture, plain view of the
> open sky, all stopped working.
> 
> Test antennas were brought in and placed on a fixture well away from the
> original antennas, the recevers went back in to capture and lock.
> 
> From what I understand, the original antennas are what I would call straight
> preamp with no pre-selection / filtering.
> 
> The ordered and now inbound replacements are said to contain a SAW filter
> system. It is the intent of the client to just place these "improved
> antennas" in to service and get on with life.
> 
> I would suspect a GPS antenna (and receiver) could be subject to RF overload
> or blocking, however, we're assuming nothing major has changed at the site,
> nor any nearby location.  One might think there are more GPS receivers
> being pushed out of reliable operation by the world around them, I'm just
> not hearing those stories from a lot of people using them (GPS receivers).
> 
> Any new install GPS receiver antenna ordered will/should contain some
> pre-selection to potentially avoid a problem, even some years down the
> road? Seems like that's where things are going... no more off the shelf,
> wide band, (hot) preamplified GPS antennas in busy locations?
> 
> Thank you in advance for any related comments and/or opions ...
> 
> cheers,
> 
> skipp
> 
> skipp025 at jah who dot calm
> ___
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