Hello,
The setup is the following:
make name type
level/attenuation
Tesla [?] T284 SWR
bridge
Rohde & Schwarz SMIQ 03 Generator
+10dBm
Rohde & Schwarz FSP 13 Spectrum Analyzer
Agilent N9355B Power limiter
-0.98dBm@10MHz
The notch filter attenuation @10MHz and @10dBm input is the following:
Att [dB] delta f [Hz]
90 0.0
80 0.1
70 0.6
60 1.6
50 4.3
40 12.7
30 40.6
20 131.5
12.76 569.2
12.22 904.1 [this is the far out attenuation of the
setup]
Disclaimer: I am not an advocate of this [notch filter] PN or PN+AN measurement
method. I just have the idea of compensating a SWR bridge having on its DUT
port an XC by a resistor at its reference port and I was amazed by its
simplicity [compared with other notch filter setups]. For the particular XC I
have used, the VSWR is not top notch as the XC proved to have some 15ohm series
resonance. So, losses given impedance mismatches shall be considered [@ the
12dB far out attenuation of the setup].
I have no deep knowledge about XCs at all and very little about their close in
noise [I can extend why, in private emails]. If this setup is useful for
somebody, it is fine. If not, it is also, fine. Do not shoot [on] me for
posting these findings.
Best regards,
Adrian
________________________________________
From: time-nuts [[email protected]] on behalf of Bob Camp
[[email protected]]
Sent: Monday, October 03, 2016 12:17 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] notch filter for close in phase noise measurement
Hi
If you do a power sweep on a crystal resonance, it’s a very predictable sort of
thing.
Essentially you “chase” the resonance up (or down) in frequency with the sweep.
At some
point, it “snaps” and drops back to the low power line. I suspect that what is
being observed
is the “snap” as the crystal stops accepting power.
In some crystals, you can get a very observable effect at a few hundred
microwatts. With
other designs it’s 10’s of microwaves or maybe even up around a milliwatt.
Liquid nitrogen cooled crystals anyone? :)
Bob
> On Oct 2, 2016, at 4:49 PM, Chuck Harris <[email protected]> wrote:
>
> That is a most interesting suggestion.
>
> Suppose the filter crystal was pulled to the DUT frequency, and due
> to the inertia of its very high Q, was able to show you the phase noise
> variations of the DUT better than one might expect?
>
> -Chuck Harris
>
>
> Bob Camp wrote:
>> .....One thing you may be seeing is the crystal shift frequency as it is
>> tuned to “accept” power from the source.
>> With milliwatts of power flying around, that would not be unusual.
>
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