[time-nuts] Any thoughts on best rubidium?

[EWKehren at aol.com]

If you want low noise in a spectrum analyzer  it all comes down to the  
signal quality into the first mixer. Every thing else with today's technology 
is  down hill.
Bert Kehren 
 
 
In a message dated 9/25/2011 5:32:31 A.M. Eastern Daylight Time,  
Robert at delien.nl writes:

> One  other thing is that some spectrum analyzers aren't really designed 
>  for low noise performance. Since the noise floor is often pretty high,  
> the design of the whole RF chain (e.g. spur levels and such) might  have 
> assumed that lots of things would be hidden in the  grass.

True, it's one of the many selection criterions for selecting  the 
instrument that meets your needs.
I've been looking a the luggable HP  series 859x and 856x, preferring the 
latter because they have a PLL YIG  whereas the fist uses a free-running 
oscillator. But these machines are old,  80's and 90's, pricey, and not really 
THAT good. Add decent range (up to 9GHz  to see recent 5.8GHz devices) and a 
tracking generator and before you know it,  you'll be paying $6k or more for 
a 20 year old instrument.

> If the  
> analyzer is of the recent "bring a band of RF down to an IF, sample  and 
> FFT it for fine resolution" architecture, such things as the  number of 
> bits in the ADC and the "cleanliness" of the sampling clock  might have 
> been chosen based upon doing 1024 point transforms being  displayed with 
> 100dB dynamic range (10dB/div and 10  divisions).

Most modern instruments do that, at least to some degree.  My R&S goes down 
to a RBW of 10Hz by just mixing. Additionally RBWs of 5,  3, 2 and 1Hz are 
achieve by additional FFT. This instrument dates from 2001,  but I don't 
think more recent instruments can achieve a mixing-only RBW of 5Hz  or below.

> (not to mention the spectrum analyzer actually  generating spurious 
> signals.  I ran across that one last year  and thought I had an 
> interference source, but, no, went back and  checked the spec sheet and 
> it said spurious are <-80dBc, and sure  enough, there it was at -82 dBc. 
>  And stories about the first LO  coming back out through the input are 
> legion.)

Gee, I wish I  had consulted this group BEFORE buying my instrument. I'm 
happy with it and I  don't regret anything, but you could have added a lot 
more arguments in favor  or against…
_______________________________________________
time-nuts  mailing list -- time-nuts at febo.com
To unsubscribe, go to  
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the  instructions there.