An SDR's sample rate only limits its bandwidth. Most devices include a mixer, which allows the transmitted or received signal to be shifted in frequency by an amount much larger than the bandwidth.
It's definitely possible to transmit multiple TV channels at once, and I have experimented with that in the past. Since TV channels are 6 to 8 MHz wide (depending on what part of the world you're in) there are practical limits to how many channels can be transmitted at once. Consumer-grade SDR boards are limited to about 56 MHz total bandwidth, which would be enough for 7-9 channels.
The cars on the map are the locations of people who are hunting for balloons after they have fallen back to earth. SondeHub's "chase mode" allows you to announce your position so that others will know you're in the area and will possibly soon collect a nearby balloon.
It would only be possible if the tuner exposed raw RF samples, the way RTL-SDR dongles do. I'm not sure whether any of the integrated FM receivers do that.
Models targeting the SDR market (e.g. from RTL-SDR Blog or NooElec) do have some improvements compared to models sold as TV tuners. Most importantly, they often include a more accurate crystal oscillator, which is useful when receiving narrow-band signals.
RTL-SDR tuners usually have very good reception between 50 and 1000 MHz, which includes the FM broadcast band. It is easy to overload the analog-to-digital converter, so it's important to make sure the gain is not set too high. Setting the gain too low could also prevent reception if you're far from the transmitter. If you're receiving from indoors, interference from electronics in your house can cause trouble, and walls attenuate radio signals. You could try moving the antenna, or check whether it works better outdoors.
Some stations send out traffic and weather images (as well as album art and station logos). The files can be dumped to disk using nrsc5's "--dump-aas-files" option. A few people have built GUIs that display the information in a more convenient way:
In addition to files, some stations also send out "stream" and "packet" data. There is ongoing work to reverse engineer the formats. See the discussion here for details: https://github.com/theori-io/nrsc5/pull/308
DVB-T could technically carry clock, weather forecasts, and alerts as text data feeds.
What needs to be done to link WEA Wireless Emergency Alerts with HD radio data streams? WX radio could possibly embed a data channel? If it doesn't already for e.g. accessible captioning?
> This system transmits compressed digital audio, digital video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing (COFDM or OFDM) modulation.
> The origins of RTL-SDR stem from mass produced DVB-T TV tuner dongles that were based on the RTL2832U chipset. [...]
> Over the years since its discovery RTL-SDR has become extremely popular and has democratized access to the radio spectrum. Now anyone including hobbyists on a budget can access the radio spectrum. It's worth noting that this sort of SDR capability would have cost hundreds or even thousands of dollars just a few years ago. The RTL-SDR is also sometimes referred to as RTL2832U, DVB-T SDR, DVB-T dongle, RTL dongle, or the "cheap software defined radio"
reply