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Re: Subject: [Discuss-gnuradio] APCO 25
From: |
Matt Ettus |
Subject: |
Re: Subject: [Discuss-gnuradio] APCO 25 |
Date: |
Tue, 21 Jan 2003 02:59:28 -0000 |
> > This sounds like a better route. I can take my IF from the output
> > of the WFM ceramic filter rather than its input so I will then only
> > have a bandwidth of 200 KHz or so. I have 10.8 MHz xtal somewhere and
> > have some SBL-1 mixers in my junkbox. Now you have set me thinking ..
> >
> > Regards
>
>
> You might have some aliases here I'm afraid. Most receivers
> (R-7000, R-7100, R8500, AOR5000-3) that have 10.7 mhz outputs have very
> wideband 6 mhz or so wide outputs designed to even handle NTSC/PAL video
> (ICOM eveb makes/made a video demod for this output). So you obviously
> need serious added selectivity if you are going to digitize the IF
> directly and aviod terrible aliases.
Why? If you are digitizing with a soundcard, it has antialiasing filters
already. Besides, you can get narrow 10.7 MHz filters that are the size of
small tantalum caps for less than a dollar from digikey.
> But these wfm filters aren't all that sharp (probably with a
> LO at 10.8 mhz the close in part of the other sideband (the image)
> would be down only 15-25 db or so). I guess you could use an
> image rejecting mixer, but these are less common in junk boxes.
see above
> The only problem with doing this with a stock FM broadcast bw
> filter (~150 khz) is that you have to be able to digitize say 200 khz
> of bandwidth with the center at around 100 khz and this rather
> implies 400 ksamples per second sampling.
Not true. Soundcards have their own antialiasing. Very good antialiasing, I
might add, since they use delta-sigma converters with very high oversampling
ratios.
Matt
Re: Subject: [Discuss-gnuradio] APCO 25, Matt Ettus, 2003/01/20
- Re: Subject: [Discuss-gnuradio] APCO 25, Ian Wraith, 2003/01/20
- Re: Subject: [Discuss-gnuradio] APCO 25, Eric Blossom, 2003/01/20
- Re: Subject: [Discuss-gnuradio] APCO 25, Ian Wraith, 2003/01/20
- Re: Subject: [Discuss-gnuradio] APCO 25, Dave Emery, 2003/01/20
- Re: Subject: [Discuss-gnuradio] APCO 25, Ian Wraith, 2003/01/21
- Re: Subject: [Discuss-gnuradio] APCO 25, Ian Wraith, 2003/01/22
Re: Subject: [Discuss-gnuradio] APCO 25,
Matt Ettus <=
Re: Subject: [Discuss-gnuradio] APCO 25, Matt Ettus, 2003/01/21