[time-nuts] Any thoughts on best rubidium?

EWKehren at aol.com EWKehren at aol.com
Mon Sep 26 11:06:06 UTC 2011


Roy
I did have a HP 8566A before replacing it with the 70000 series. Same size  
and weight.
Bert Kehren
 
 
In a message dated 9/26/2011 6:27:59 A.M. Eastern Daylight Time,  
phill.r1 at btinternet.com writes:

Bert
What's your opinion of the "old" HP8568B  with its  max. frequency range of 
1.3 Ghz and its weight of around 100 lbs. - are  the more recent 
instruments 
that much better  ?
Roy


--------------------------------------------------
From:  <EWKehren at aol.com>
Sent: Sunday, September 25, 2011 10:47 AM
To:  <time-nuts at febo.com>
Subject: Re: [time-nuts] Any thoughts on best  rubidium?

> 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…
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