Re: [Discuss-gnuradio] USRP Custom Filter Taps

[Daniel Garcia]

Matt Ettus wrote:
>Yes, you can change the filter taps in the FPGA.  See the halfband (HB)
> verilog code.

Thanks! I'll take a look.

>> I read on a previous thread that it is possible to invert the spectrum of 
>> the sampled signal so that the tuned frequency would be the FM carrier. The 
>> end result being a stream from the USRP where 0 Hz is the center frequency 
>> of the audio carrier the the video carrier is at 4.5 MHz. Is this possible? 
>> The advantage here is that the base-band audio does not need to be shifted 
>> before FM demodulation; also the video carrier does not need to be shifted 
>> before demodulation (AM). 
>
>Not sure what you're looking for here.

After thinking about it, I'm not sure either. I figured I can to tune to FM 
carrier to the center frequency (0Hz), set the decimation to 4 (16 MS) and the 
video carrier is at -4.5MHz. Unfortunately, my USB/computer can't handle can't 
handle the 16 MS rate. I was hoping to avoid translating the signal by placing 
the FM signal at 0Hz. Since my PC can't handle that data rate,  I'm just going 
to concentrate on the NTSC. 

-Daniel


As an aside: It would be nice to have something like the GC4014 on-board the 
USRP. In my application it could be used to tune the video and audio signals on 
separate receiver channels without using up resources on the PC (and also 
reduce the need for a faster interface in some cases). Not sure if there's 
enough room on the FPGA though.