[time-nuts] E4437B phase noise spurs. Any ideas?

[Bill Byrom]

Sorry - I forgot that this list server only distributes plain text
messages, so my two images from the HP/Agilent/Keysight ESG and
Rohde&Schwarz SMIQ datasheets were not included. Please see the two
attachments.

--
Bill Byrom N5BB
Tektronix RF Application Engineer
 
On Fri, Jul 17, 2015, at 12:47 AM, Bill Byrom wrote:
> Hi, Wolfgang. Both of your generators appear to be well within their
> datasheet specifications based on the spectrums you posted.
>  
> The datasheet for that ESG-DP (digital modulation with high spectral
> purity) model is at:
> http://cp.literature.agilent.com/litweb/pdf/5965-3096E.pdf
>  
> The E4437B nonharmonic spur specification is on page 5 (use the ESG-
> DP columns):
>  
> So according to that table, above 2 GHz the E4437B spurs at >3 kHz
> offset **should be below -68 dBc**. It appears to me that the largest
> spur at such offsets (at about +3.5 kHz offset from the carrier) is
> **actually about -74 dBc**. The largest spur is about -63 dBc at +1 kHz
> offset (which is closer than the spur specs).
>  
>  
> The R&S SMIQ03B specs are:
>  
>  
> The SMIQ03B nearby spurs in your screen capture are at about +/- 9 kHz
> offset from the carrier (about -85 dBc), so are too close to be covered
> by the spec above. The spurs at >10 kHz offset are about -90 dBc.
>  
> I'm guessing that the spurs might be affected by several adjustments
> performed during factory alignment. In most modern complex instruments
> (including both of these signal generators, I believe) there are far too
> many alignments to be made by a human, and a long automated process
> using a rack of equipment is used to align the instrument and store
> certain constants in nonvolatile memory in the instrument. But there is
> no reason to worry based on your results, since they are well within
> instrument specifications.
>  
> So ... assuming that the spurs aren't coming from your spectrum analyzer
> or other sources (and I'm guessing that's a FSU which is very good),
> both generators appear to be within specifications (after warmup within
> the calibration interval, of course).
> * *The E4437B closest spur covered by the >3 kHz spec is at about +3.5
>   kHz, and it's about 6 dB better than the spec.*
> * The SMIQ03B has a 6 dB better spurious spec than the E4437B between 2
>   and 3 GHz, but the SMIQ offset for their spur spec is wider than the
>   ESG (10 kHz rather than 3 kHz).
> * At other carrier frequencies the spurs may be higher or lower in
>   amplitude (and at different offsets). Try tuning the frequency in 1
>   kHz steps over a wide range -- I would guess that the spur offsets
>   and levels will change in a complex fashion due to the synthesizer.
> * The phase noise specifications normally apply to a smoothed trace and
>   do not include narrowband spurs such as the ones you see in your
>   screen capture.
> --
> Bill Byrom N5BB
> Tektronix RF Application Engineer
>  
>  
> On Thu, Jul 16, 2015, at 04:15 AM, Wolfgang DL1SKY wrote:
>> Hi,
>>  
>> I just got a used/refurbished E4437B which I wanted to use as a
>> all-purpose RF generator primarily for 3-4 GHz.
>>  
>> Unfortunately, I'm seeing strange spurs for frequencies above 2.4 GHz,
>> see the green curve in the attached image.
>> The yellow curve is an SMIQ03 for comparison.
>>  
>> Observations:
>>  
>> - For frequencies below 2.4 GHz none of the spurs appear.
>>  
>> - It has an OCXO and I left the device in standby (oven on) for
>>   12 hours.
>>  
>> - If I leave the device ON for 1-2 hours, the spurs go down.
>>  
>> Anybody else seeing this? Any ideas how to fix this? Does this look
>> like a pre-failure sign?
>>  
>> Regards,
>> Wolfgang DL1SKY
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>> Email had 1 attachment:
>  
>  
>> * E4437B-phase_noise_problem-1.png
>>   34k (image/png)
>  
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