Narrow band RF filter options
Carbon_Rod, Tue Jan 22 2019, 07:40AMI 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
Re: Narrow band RF filter options
2Spoons, Tue Jan 22 2019, 09:45PM
So you want a filter with a Q of about 500,000.
That seems unlikely to me.
2Spoons, Tue Jan 22 2019, 09:45PM
So you want a filter with a Q of about 500,000.
That seems unlikely to me.
Re: Narrow band RF filter options
Sulaiman, Tue Jan 22 2019, 10:06PM
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)
Sulaiman, Tue Jan 22 2019, 10:06PM
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)
Re: Narrow band RF filter options
Plasma, Tue Jan 22 2019, 10:09PM
Would a MOV with some signal basis filter it.
No experience in the above.
Plasma, Tue Jan 22 2019, 10:09PM
Would a MOV with some signal basis filter it.
No experience in the above.
Re: Narrow band RF filter options
2Spoons, Tue Jan 22 2019, 11:11PM
I agree with sulaiman: superhet would be the more practical approach for a narrow band receiver.
2Spoons, Tue Jan 22 2019, 11:11PM
I agree with sulaiman: superhet would be the more practical approach for a narrow band receiver.
Re: Narrow band RF filter options
Carbon_Rod, Wed Jan 23 2019, 08:30PM
@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.
=)
Carbon_Rod, Wed Jan 23 2019, 08:30PM
@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.
=)
Re: Narrow band RF filter options
johnf, Thu Jan 24 2019, 06:19PM
BAW filters already exist for this, maybe not the desired Q, but cascading slightly differing models would get close
johnf, Thu Jan 24 2019, 06:19PM
BAW filters already exist for this, maybe not the desired Q, but cascading slightly differing models would get close
Re: Narrow band RF filter options
Sulaiman, Thu Jan 24 2019, 09:29PM
unless frequency mixing is involved.
You are using homodyne detection ?
How ?
Maybe you mean heterodyne ?
Sulaiman, Thu Jan 24 2019, 09:29PM
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,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
unless frequency mixing is involved.
You are using homodyne detection ?
How ?
Maybe you mean heterodyne ?
Re: Narrow band RF filter options
Carbon_Rod, Fri Jan 25 2019, 12:48AM
@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..
Cheers,
Rod
Carbon_Rod, Fri Jan 25 2019, 12:48AM
@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..
Cheers,
Rod
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