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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I've not tried this model but an SDR would work
for a lot more work (tuneable down-converter front end) you could use the much cheaper usb SDR types
Judging by the older stuff that I have, and the newer stuff available, a cheap SDR for your frequencies of interest should be available soon.
If you are doing relative measurements then the above will work, if you want absolute measurements then the internal oscillators will not be stable or repeatable enough, you will need something like a rubidium-based oscillator for the mixer clock(s)
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
@2Spoons superhet is usually better for most types of problems as the fractional bandwidth of a filter design remains nearly the same, but the absolute bandwidth is much more narrow at a lower frequency.
This was not what I'm looking for, but thank you for the replies. =)
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Carbon_Rod wrote ...
I am looking for a tune-able or select-able filter with a very narrow pass-band under 5kHz wide at 1.2 to 2.5 GHz.
Does anyone know of such a device maker?
I am trying to measure orbital Doppler shifts with a homodyne receiver.
Cheers, Rod
I do not believe that there is such a thing as a very low bandwidth, GHz range, tuneable filter that is practical, unless frequency mixing is involved.
You are using homodyne detection ? How ? Maybe you mean heterodyne ?
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
@johnf I came to the same conclusion of using bypass signal switching, chaining bpf windows, and managed to find a few sub 10Mhz-ish bw SAW filters that look promising given they overlap the area of interest. Unfortunately, this design also means the insertion losses will necessitate an awful lot wrangling to get it to behave as each stage will need a matching network, and the noise floor may ultimately come up too high to grab the weaker signals.
@Sulaiman Indeed, some trivial problems can get ridiculous rather quickly. Yet if it were easy it wouldn't be any fun.. I may end up having to stick everything in a temperature controlled oven to keep the tuning stable, but I can only handle one issue at a time..
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Narrow band RF filter options
