[time-nuts] crystal notch filter // numbers

[Bob Camp]

Hi

Nice data !!!

Thanks for posting it.

Bob

> On Oct 3, 2016, at 1:29 PM, Adrian Rus <adrian.rus at broadhurst.ro> wrote:
> 
> 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 at 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 [time-nuts-bounces at febo.com] on behalf of Bob Camp [kb8tq at n1k.org]
> 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 <cfharris at erols.com> 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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