[time-nuts] Ebay FE-5680A Rb: Are they that good?

Javier Herrero jherrero at hvsistemas.es
Fri Dec 9 12:23:16 EST 2011


El 09/12/2011 17:51, ed breya escribió:
> When looking at harmonic distortion of the 10 MHz, also consider the 
> distortion of the SA itself. I rebuilt my filter made from LAN 
> components that I described a while back, and achieved about 85 dB 
> rejection from 30 MHz to 70 MHz, which should have made harmonics of 
> even a crappy sine wave all but disappear. When I put actual signals 
> through it, I was shocked to see that it hardly made a difference - it 
> seems that the SA mixer provided way more distortion than what I was 
> looking for, making it impossible to tell if the filter worked.
Good point. I've checked it and the 8566B is spec for 2nd harmonic at 
<-70dBc (100Hz-50MHz, 50-700MHz) and <-80dBc (50-700MHz), but at <-40dBm 
mixer input. In my measurement, mixer input ins around -14dBm, and the 
second harmonic is a around -68dBc, so not bad. I can compare also with 
a Tek 495 (I first did a quick check of the Rb output with it, because I 
have it at a nearer distance in the lab...) but as far as I remember, 
results were more or less the same.
>
>
>
> I gave up trying to measure the filter response to actual signals at 
> that point, until I review the 8566B specs. I assume that performance 
> limit was one of the reasons why HP offered a low-band preselector.
>
I think that the low-band preselector (I don't remember the model) was 
more oriented to increase the dynamic range for EMC testing, rather than 
due to a crappy harmonic response of the analyzer. It also includes a 
preamplifier.

Regards,

Javier





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