odd results working at 250ksp/s
246tnt at gmail.com
Tue Oct 22 08:29:28 UTC 2013
> I don't understand what is happening here. 1 MHz is an even multiple of
> 250kHz, so maybe I'm getting an image of OAK overpowering the relatively
> weaker SFO signal. But should there not be filters that manage this?
Yes most likely an image.
> I guess I was expecting that if the device is set to 250ksps, then it would
> "close down" filters appropriately to reject signals out of that band. But
> maybe the filters don't work properly below a certain sample rate? Like the
> rtl2832 can sample down to 250ksps, but the 820T tuner was not designed for
The filters you'd need wouldn't be in the R820T anyway (it has filters
but not that narrow).
IIRC, the rtl2832 always sample at a fixed high frequency but it has
an internal downconverter + FIR filter inside to convert the sample
rate down. But that FIR probably can't handle such a big reduction ...
> Can I control the filters directly?
If you find out, let us know, but AFAIK all attempts so far didn't
succeed to get it more narrow than this.
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