22 kHz problem

General information

Some DVB-s cards have problems switching the LNB to the High Band. You will be able to receive channels on the low band but nothing on the High Band. This is due to some LNBs which are very picky about the 22 kHz switching signal. For example, my card has a 24 kHz switching signal.

For a solution you can either change your LNB (see below), or do some soldering. The DVBs card has ST's SP13 or SP16 LNB power chip. It has got an unused input that can be used for the switching signal. The idea is to use a weak signal on the unused pin that cannot switch the LNB alone; but together with the "wrong" signal it will switch the LNB.

A 22 kHz generator is needed. Documentation for the LNB power chip is available at http://us.st.com/stonline/index.shtml (use the search function). For me the variable resistor is at 600 Ohm.

A drawing and some photos of the finished work:

circuit drawing LNB power chip regulator

modified card

Here is a short list of working/not reliable working LNB's and DiSEqC Switches. If you like to contribute, please send a mail to Henning Holtschneider.

If you receive only transmissions on the vertical polarisation, the reason is that the LNB is not switched by the 18V the card provides to the horizontal polarisation. That's a different problem.

© 2001,2002 Jörg Riechardt