HI > On Apr 9, 2017, at 4:28 PM, Attila Kinali <att...@kinali.ch> wrote: > > On Tue, 4 Apr 2017 17:58:11 -0700 > jimlux <jim...@earthlink.net> wrote: > >>> The advantage of such a system would be that there is only a single >>> path through the system for all signals, especially through the filters. >>> Thus the variability of the differential phase shift between the >>> frequency bands would be significantly reduced, which would result >>> in better stability. >> >> Oh, I'm not sure about that. It would depend on the filter kind and >> topology. >> >> If it's a SAW or BAW filter, it's all one "brick", but I think you'd >> still need to calibrate the differential phase shift vs temp. And it >> might be very predictable in a "measure 10 of them, and now you know the >> characteristics of the next 1000" > > 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? Bob > And at the same time, because the IF frequency > being low, you don't need any specialized filter components that > might not be available in a couple of months. > > Of course, this doesn't really work that way when significantly > wider signals (E5) have to be caught together with "narrow band" > signals (L1 C/A or L2C). > > >> >> Of course, that's the theory. Whether things work >>> out this way in reality is a different question. What can be said for >>> sure is, because of the high IF frequency of >200MHz, the standard tuner >>> chips cannot be used anymore and the RX chain has to be build from >>> "discrete" components, >> >> There's a ton of integrated demodulator/ADC parts out there these days >> that go up to 6GHz. >> AD9361 for example >> >> it will do 56 MHz BW through the IF, with 12 bit ADC feeding a 128 tap >> FIR filter, etc. > > Unfortunately, the AD9361 does not offer the IF bandwith necessary. > Even though it has a high sample rate and can offer high bandwidth > capture of signals, the zero-IF nature of its design doesn't work > for this design approach. The IF of the AD9361 has a low pass filter > of at most 56MHz, ie it offers to capture a bandwith of 56MHz of > frequency space (using both I and Q channels). But the above approach > would need an IF of >200MHz, but it would be enough to only have a > single channel. > > I looked up the prices for the components and figured that the prices for > mixer and IF amplifiers are actually quite low (a 2-4 USD per IC) so it > isn't that much more expensive to build such a system than using a 3 tuner > approach (eg using MAX2120 as Peter Monta did with the GNSS Firehose). > > 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 > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.