[time-nuts] Any thoughts on best rubidium?

[Roy Phillips]

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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