Bob, Using the approach you described I was able to verify the noise
floor of my initial measurement setup to be at -80dBc at 10Hz offset
from carrier and -100dBc above 1kHz with a strong peaks at 50Hz, 60Hz
and harmonics. This all with an RBW in the FFT of around 4Hz.
This level of noise is
Hi
With an audio spectrum analyzer, and an RPD-1 mixer, and +10 dbm on
each side of the mixer …. you should be able to get away with about 20 db
of “preamp gain”. Yes, that’s dependent on exactly what analyzer you have.
The typical sound card may well need closer to 50 db of gain. That’s better
Hi
Ok, single mixer phase noise basics:
First thing is to womp the mixer up to the point it almost smokes. Putting +7
dbm into
both ports on a “7 dbm” mixer is very normal in this case. Watching for the
fact that the
mixer likely is *not* a 50 ohm load is part of the process ( = pads might
Hi Jim,
On 2022-06-20 17:57, Lux, Jim via time-nuts wrote:
On 6/20/22 2:39 AM, Magnus Danielson via time-nuts wrote:
So, a counter is really like an ADC for phase, with wide bandwidth
input and a sub-sampling mechanism (trigger/time-base). Through
processing frequency estimates can be
I found the info on how to calibrate and lots of other practical stuff in
here: https://martein.home.xs4all.nl/pa3ake/hmode/dds_pmnoise_pll.html
Erik
On Mon, Jun 20, 2022, 19:43 Erik Kaashoek wrote:
> Bob, Magnus,
> Thanks, clear. A counter is for ADEV, not for phase noise.
> I made a test
Bob, Magnus,
Thanks, clear. A counter is for ADEV, not for phase noise.
I made a test setup to learn how to use the mixer/PLL approach.
First using 10MHz from both outputs of a DSS (Rigol DG990) to observe
the DC shift with shifting the phase between the two signal.
Then by modulating one
Hi
A “proper” phase noise analyzer will get you down to < -165 dbc/Hz. It also
will preserve
the frequency spectrum ( no sampling / nyquist roll over ). What you get at 132
Hz offset
is the (DSB) noise at that offset and *only* that noise.
With a counter ( as Magnus mentions ) the sampling
On 6/20/22 2:39 AM, Magnus Danielson via time-nuts wrote:
So, a counter is really like an ADC for phase, with wide bandwidth
input and a sub-sampling mechanism (trigger/time-base). Through
processing frequency estimates can be provided. Aliasing occurrs in
the sub-sampling. Modern counters
Erik,
A counter actually measures a number of phase measurements. Then, as you
process that you get a frequency readout based on the difference between
them (event-count divided by time between phase measurements). Now, as
you want to do frequency read-out, you can do a handful of filtering
Hi
Bob, many thanks for your explanations/recommendations and links.
According your advices I will try to make PN measurement on new SA with
cross-correlation to get more clear picture of the output signals.
The next my step will be a quadrature method measurement and comparison of
Bob,
Many thanks for the guidance you provide and the phase noise measurement
document.
Can you provide feedback on this reasoning: A counter is like an ADC but
in the frequency domain. So if you measure with 0.01 s tau you basically
average over 0.01 s so you can only observe "phase noise"
Hi
As HP found out back around 1973 or so, translating ADEV to phase noise
is not possible. This is true, even if you have the ADEV numbers for a variety
of Tau values as opposed to some sort of “average” kind of number.
There are a number of things ( like spurs ) that can strongly influence a
Hi
Thank you for the clarification and rf-tools link.
Agree with your calculation. That’s why I raised this question regarding a
fixing PN degradation by Pendulum CNT-91.
Could you please explain where is the error in my reasoning of the experiment :
* There is one 10 MHz
Hi
If the objective is “phase noise -130 dbc at a 10 KHz offset” and the signal is
at 25 MHz, the resultant jitter ( in a 10 KHz bandwidth ) is likely in the <
500 fs
range. The CNT-91 is only a 50 ps resolution device.
Since it’s a counter, there is no practical way to vary the bandwidth.
Hi
> The CNT-91 has a very high noise floor if you are trying to “see” phase noise.
May be but with this Pendulum CNT-91 I can fix PN degradation in the range -130
... -150 dBc/Hz where R FSQ8 can do nothing...
FYI: FSQ8 is not the worst SA: PN floor -130 dBc/Hz @10 kHz on 1 GHz.
Karen,
Hi
The CNT-91 has a very high noise floor if you are trying to “see”
phase noise. It also does not give you much in the way of frequency
offset information. A single mixer setup running into a sound card
is a *much* better approach if you are looking for another opinion
vs the FSQ8. I have used
Hi Bob,
Thank you for the advice. An issue with PN of 25 MHz reference source has been
decided - I found the PN source, changed schematic and now all works well.
My question is about an opportunity to fix PN degradation by Pendulum CNT-91
frequency meter-analyzer (which I measure the Allan
Hi
The “typical” approach to doing this is to multiply up to something around
100 MHz with a relatively narrowband PLL. You can get ( or build ) VCXO’s
in this range with phase noise (at 10KHz offset) in the 160’s to (maybe) 170’s.
This is much better performance than a 5 or 10 MHz reference can
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