We recently moved home, and I'm looking at installing a dish at the new place. I've invested in a satellite finder, but discovered it requires a 13-18v feed on the co-ax to function. Do DVB-T PC tuner cards such at the S350 send power down the line to achieve this, or will I have to rig up some kind of Heath Robinson power supply myself?!
Sorry if I'm being pedantic (because we all understand your question) but the S350 and satellites in general are DVB-S.
Now, an idiot's guide to LNB: (or should that be an LNB guide from an idiot?).
Satellites use very high frequencies between 9-10GHz and tv receivers only like to work in the range 900-1500MHz. At both ends, the tv signal is superimposed on these signal frequencies (known as carriers). The incoming high frequency to the lnb is combined with an intermediate frequency signal (supplied by a local oscillator built into the lnb) which has the effect of reducing the resultant carrier frequency down to 900-1500MHz which can be handled by the receiver built into the tv or tuner card.
Now very quickly, the number of signals that could be carried by a simple satellite transmitter became saturated so methods had to be created to increase the capacity.
One way was to double the capacity by using polarised signals. This means that the radio waves come out like ripples on a pond: in this case horizontally. If you float a sheet of plywood on the water it will go up and down ie detect the wave. If you placed the plywood vertically in the water in the line of the emerging ripples, it will not move or detect the wave. Electronically, it is easy to rotate the transmission signals so that thay are vertically radiated. Detection is simple: both types of signal are received into the round lnb port (tube). In the bottom or top of the port is a pin a few mm long. This pin acts as a receiver but only detects the vertical signals. In either side is a horizontal pin which only detects the horizontal signals. All that is required is an electronic switch that selects either pin and this switch is controlled by the application of a dc voltage of either 13 or 19V. This is supplied by the tv or tuner card.
To further increase the capacity of the satellite, more frequency bands needed to be used. The problem that then arose was that when these wider frequencies were mixed with the local oscillator in the lnb, the resultant frequencies were outside of the range that the tvs/tuners could handle. What was needed was the ability to change the frequency of the local oscillator in the lnb so that the resultant frequency was acceptable to the tv/tuner. The local oscillator is modified by the injection of a 22KHz tone from the tv/tuner.
There are lots of filters etc also in the lnb but in a nutshell that is how this "idiot" understands it to work! Lots more can be got from here: Satellite LNB: What is it, how does it work and where do I buy one?