Re: [sdr-radio-com] Re: Request - increase FM bandwidth to 240kHz
- Here's a screen shot of one of our FM HD transmitters running Hybrid
mode at -14 dBc injection. In the upper left is the spectrum view that
shows the signal within the mask.
"A closed mouth gathers no feet"
That "within the mask" was what I had been seeing here in North America FM broadcasters...
...and Bill and Simon have the point to expand the SDR-Radio bandwidth to 250 to 256K, with my humble vote to make it 256K, as it's both a nice standard point, and it also allows us to make sure that a FM signal is not outside of "the mask".
--- In email@example.com, Mike Seguin <n1jez@...> wrote:
> Here's a screen shot of one of our FM HD transmitters running Hybrid
> mode at -14 dBc injection. In the upper left is the spectrum view that
> shows the signal within the mask.
> Mike, N1JEZ
> "A closed mouth gathers no feet"
- I think that we need at least a filter being able for as much as 300 KHz wide.Nominal FM deviation is +/-75 KHz peaks, altough many badly adjusted stations use more than those 75 as maximum FM deviation.Frequency Modulation methods create infinite number of sidebands, occupying an infinite spectrum up and down the niminal frequency, but Carson rule says that 98% of the transmitted energy occupies only 2 x (peak deviation + maximum baseband frequency) = 2x(75+99)=384 KHz, for a transmission full of possible associated services, and in this case receiver should be able to receive a 384 KHz wide signal.FCC says that 400 KHz spacing is about right, but here in Europe we don't use that much baseband, let's say 59KHz only for a Stereo and RDS. instead of 99, so our required BW would be 2x(75+59)=268KHz instead of 384. We need to receive at least 268KHz wide, assuming that not a single station exceeded those 75 deviation peaks. Spacing of 300KHz should be OK for us.Have a look here: