[time-nuts] Sinlge ADC multi-band receiver

[Attila Kinali]

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
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson