Measuring LNB Supply Voltages

Satellite TV tuners are wonderful things, when they work. When they don’t, it might be a faulty LNB Supply chip - or it could be mis-programmed in your driver. How do you debug that?

All satellite tuners use LNB Supply and Voltage Control chips to output 13/18V on to the coax cable, which in turn connects to your out-door satellite dish. Various manufacturers make these supply chips, here’s one example (and datasheet) from Alegro.

The 13 or 18V supply instructs the LNB unit, mounted at the focal point in front of your dish, to downshift and output particular bands of RF spectrum, so that your TV tuner can receive these radio frequencies. LNBs shift very high frequencies received from satellites in Ku band (11-13GHz) down in frequency into the L-Band (1-1.5GHz). These L-Band frequencies are much easier for set-top-boxes and PC add-in tuners to digest.

As a device driver developer, you’ll need to be able to measure the voltage properly in order to debug the hardware. Here’s a simple hardware trick that helps, it works with every satellite TV tuner on the market today.

Take a standard female to male f-type connector, break off one of the outer shields, so that you can see the inner core of the connector. Create a large hole by working one piece of the outer shield back and forth, use a pair of needle-nose pliers. It will eventually break off.

The hole should easily be big enough to connect to your TV tuner as well as leaving enough room to connect a probe. You can now measure the LNB Supply chip output, which should be 13 or 18V.

… and if your meter shows zero volts, perhaps you’ve identified your driver tuning bug - or finally confirmed its faulty hardware.

Keep the modified connector somewhere safe, it will come in handy again.