Building a good YIG based synthesizer has its challenges i admitt, first problem is that usually YIGs are not as good in phasenoise to begin with, next thing is that you have to design your drivers carefully and use really low noise powersupplies and filtering, one issue is that with the tuning range of the YIG beein much wider than of a VCO noise and interference on the psu and tuning lines will take its toll on the phasenoise so even the driver and associated lines need to be shielded and filtered.
Next is the approach on how to reduce the Frequency, a frequency divider is nice however there are not too many out there covering 2-18GHz that offer low noise, another approach is to use a harmonic mixer to down convert the Signal to a lower IF range and then prescale and go to a PLL.
Generally it never hurts to look at what HP did , study the design and learn from it, one thing about the 8566 is that it uses a 3-6GHz YIG and for some reason 3-6GHZ seems to be a sweet spot for low phasenoise, at least you get the idea if you look at datasheets, most low phasenoise YIGS are 3-6GHz, dont ask me why
John Miles <jmiles@...> wrote:
> Hi John,
Yes I have seen that unit - I was pondering something more
sophisticated. Along the lines of 100MSa/s to FPGA to digitize x,y or
if and an embedded web-server to get the data out.
Keep in mind that there's no benefit to digitizing post-detected trace
signals (x and y) at rates beyond the bandwidth of the widest video filter,
typically a few MHz at most. And if you digitize the final IF, the
bandwidth may still be limited to a few MHz by other filters in the SA's
signal chain.
If you are that ambitious, I think the best approach -- meaning, the one
that would benefit others the most, and require you to do the least original
engineering work -- would be to launch a project using the USRP or other GNU
Radio peripherals as a general-purpose spectrum analyzer back end. Keep it
simple at first or you'll never get anywhere! Trust me on that...
I figure I might
have enough space on that board and use the control inputs for other
purposes such as selected storage mode or other function since they
wouldn't be controlling the tube any more. Still early ponderances -
I only just got the SA and need to play with it a bit more!! I've
decided its time to move into the exciting world of RF and high speed
digital - spent enough of time on slow - medium speed digital and
software - besides - that's what I do at work.
It's definitely a good idea to spend time coming to grips with the
limitations of what you have. The obvious specification deficiencies aren't
always the ones that will end up limiting your measurements.
I was interested in your hybrid 2GHz vco and possible use as a yig
stabilizer.
Heh... that will teach you all you (n)ever wanted to know about noise and
stability. Building a clean YIG synthesizer is a challenging project. I
still haven't managed to do as well as the old HP designs, even with
much-newer opamps and other parts... which is one reason I chickened out
when I realized I was faced with that sort of problem in my 8566 'redesign'
project. It will have to wait until I can devote a lot more time to it.
I just realised that we looked at using your pc sound system where I
work. We're now moving from SGIs into pcs and may be looking at it
again. :-)
Oh, you mean the sound system I'm supposed to be working on right now. Oh,
yeah, THAT. :)
-- john, KE5FX
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