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
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From: <ewkeh...@aol.com>
Sent: Sunday, September 25, 2011 10:47 AM
To: <time-nuts@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,
rob...@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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