Generally you can get up to a sample rate of ~2.4e6 samples per second before packet loss, which gives 2.4MHz bandwidth. Remember the output of an rtl-sdr are IQ samples, interleaved in-phase and quadrature, this allows you to distinguish between positive and negative frequencies so you'll receive 1.2MHz on both sides of the center frequency for a total of 2.4MHz.
-Doug On Sun, Sep 14, 2014 at 11:57 PM, Adam Nielsen <[email protected]> wrote: > > Found an interesting program RTLSDR-Airband > > https://github.com/microtony/RTLSDR-Airband > > > > Which allows up to 8 channels to monitored and fed to Icecast > > servers... > > Oh looks nice! I will investigate, hopefully this is easier than > manually clicking around trying to listen to active channels as you > visually spot a transmission. > > > The setup requires a center frequency to be used and then the > > channels monitored need to be withing some "bandwidth" of the SDR > > device used... > > > > *BUT* > > > > What is this max bandwidth allowed??? > > Depends on what you set it to. As you'll see one of the first specs > listed for any SDR device is the maximum bandwidth possible, and for > RTL2832 devices it's generally around 2MHz, but you can go over 3MHz if > you don't mind the odd bit of signal loss here and there. > > This means you can decode say 2MHz of the RF spectrum at a time. > Where is up to you - you could choose to decode from 120MHz to 122MHz, > or from 121MHz to 123MHz, and so on. But two of the channels you list > (120.65 and 124.5) are more than 2MHz apart, so you wouldn't be able to > listen to these two at the same time. > > The centre frequency is just the middle of the two extremes, so tuning > to 120MHz with a bandwidth of 2MHz will get you 119.0 through to > 121.0. Note that an actual broadcast at 119.0 will go below 119.0 a > little, so you should consider any channel at the extreme of the range > unavailable for decoding. > > > Is this within in the "Max Bandwidth" of these E4K and RTL283U > > devicess??? > > As above, generally you will have to stick to 2-3MHz so not all of > those channels are within range. You will need a second device, or > a different device with larger bandwidth, to receive them all at the > same time. > > > The README never seems to outline what this, how I would find it, > > etc... > > Don't take this the wrong way, but it's such a basic specification when > you select your SDR device that it's taken for granted you know what it > means :-) > > > Is this within the bandwidth of these SDR units??? Or something > > narrower??? And thus 2-3 dongles are needed??? I could narrow this > > down... a little more to: > > > > 121.500 > > 124.500 > > 122.950 > > 121.400 > > This spread is 3.1MHz which is so close to the upper limit of 3.2MHz you > may just be able to scrape through, but you will definitely experience > some packet loss. > > > But the prime two targets 124.500 and 121.4 with their ~ 3MHz > > separation I see being a problem.. > > Yes, you might just be able to get these two but you will likely get > some interruptions as USB packets are dropped due to limitations of the > RTL2832 chip. You might be better off getting a second device. > > Cheers, > Adam. > >
