"John Miles" wrote in message
...
In article ,
says...

The W7ZOI homebrew spectrum analyzer article is not to be missed:

http://www.qsl.net/n9zia/wireless/pdf/9808035.pdf (part 1)
http://www.qsl.net/n9zia/wireless/pdf/9809037.pdf (part 2)

You'll find this design vastly superior to the "poor man's spectrum
analyzer" projects out there that are based on CATV tuners.

The W7ZOI project is very interesting. I'm interested in what ways you
think
it's superior to the poor man's spectrum analysers based on CATV tuners?
The
latter surely have greater frequency coverage. But in what ways are they
inferior and can you quantify it?

Apart from what Ian said, it's also really important to have a stable
LO. If you don't -- i.e., you're relying on an inadequately-stabilized
cable TV tuner -- you can only tell if a signal is present or absent.
You can't tell much about its stability and noise level, or look for
close-in IMD products. Narrow resolution bandwidths require stable LOs.

I haven't used a W7ZOI analyzer myself, but it ought to be at least an
order of magnitude more stable than any CATV implementation. It would
indeed be interesting to see a spec-for-spec comparison between the two.

The W7ZOI analyser uses a mini-circuits VCO. I couldn't find any stability
data on the minicricuits website, do you know of a source?
I suppose oscillator phase noise is also important. I'm interested in why a
minicircuits VCO should be an order of magnitude more stable than a CATV or
UHF TV tuner's VCO? I have a UHF tuner here (470-862MHz). The tuning voltage
(approx 1-25V) is stabilised by a simple zener diode arrangement. Even when
left on for hours tuned to a TV station, no re-tuning is necessary. As far
as I can tell there is no AFC employed.


Either way, they make great educational projects.


Agreed!

Hans G0UPL

Oscillator phase noise will show up as noise sidebands on the signals
you're measuring. They'll limit your ability to use your spectrum
analyzer to judge the noise that's really coming from the signals. As a
very good and professional engineer who spent a number of years
designing some of the best commercial spectrum analyzers made, Wes most
certainly paid a great deal of attention to phase noise and dynamic
range, two of the most important potentially limiting factors of
spectrum analyzer performance.

Roy Lewallen, W7EL

Hans Summers wrote:

. . .
I suppose oscillator phase noise is also important. . .

Oscillator phase noise will show up as noise sidebands on the signals
you're measuring. They'll limit your ability to use your spectrum
analyzer to judge the noise that's really coming from the signals. As a
very good and professional engineer who spent a number of years
designing some of the best commercial spectrum analyzers made, Wes most
certainly paid a great deal of attention to phase noise and dynamic
range, two of the most important potentially limiting factors of
spectrum analyzer performance.

Roy Lewallen, W7EL

Hans Summers wrote:

. . .
I suppose oscillator phase noise is also important. . .