[time-nuts] Sinlge ADC multi-band receiver
alex at pcscons.com
Mon Apr 10 19:39:09 EDT 2017
depend how much in-band loss could you afford it is relative easy to
make cavity filters if you have a network analyzer available
On 4/10/2017 9:11 AM, Attila Kinali wrote:
> On Sun, 9 Apr 2017 18:13:48 -0400
> Bob kb8tq <kb8tq at n1k.org> wrote:
>>> The beauty of the system would be that you don't need a SAW filter
>>> at all. If the input stage (LNA + mixer) has a high enough dynamic
>>> range, then the (first) IF filer alone can remove all those out of
>>> band interference.
>> Why would you substitute an expensive IF filter for a cheap front end filter?
> Availability: Although there are L1/L2 filters available, they are not
> easy to get unless you buy them in bulk. The standard L1 filters you
> can buy are rather narrow band (just 2-4MHz) and don't allow the
> reception of the modern signals. L5 filters are very rare and E5 filters
> simply do not exist yet.
> And keep in mind that the IF filter does not need to be a special
> ultra-steep filter. The high sampling rate of the ADC allows to place
> the input signal such, that the stop band can be quite far from the
> pass band. Also, the filter is only really necessary to filter out
> narrow band interference, which is hopefully far from the signal anyways.
> Having a bit of noise fold in is, as Jim noted earlier, not a problem at all.
> Attila Kinali
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