[n00p]

an LNB (the thing that goes in the focus of a parabolic antena) is really cheap and easy to power

the probem would be that the cheap dtv (RTL-SDR) only gets up to 2.4MHz of spectrum bandwith, a typical DVB-S mux can be around 20MHz or the DVB-T terrestrial standard, 8MHz

[galangalalgol]

The LNBs on ebay are pretty cheap but the intermediate frequency some of them use use is a bit too high. And as you say. You'd just be finding some slice of the signal without any hope of demodulation. I still think a microphone or rtl are a great way to play with gnuradio companion. Lime sdr is probably the next step up in price.

[wdfx]

How can the DVB-T signal bandwidth be larger than what the 'dtv' receiver is capable of if that device was actually originally designed to receive exactly that class of signal?

[mimanning]

The 2.8 MHz limitation comes from shipping raw RF samples off the device over USB 2. When operating as a DVB-T receiver the device decodes the signals before sending them over USB so it uses less bandwidth.

The device was originally intended only as a dtv receiver and not a general purpose software defined radio. The hobbyist/ hacker community discovered the hidden debug mode that allows raw data acquisition and wrote drivers for it.