LNB FAINT PATTERNING TYPE INTERFERENCE

 

This is not really a cure but a Pointer into the fact that when using LNB's for narrow band FM you sometimes get patterning at the back of the picture.

After a lot of effort to trace this...............it is there on MOST LNB's.

The cause is the RF FET negative bias generator that can run from 10KHz to 100KHz and does seem to modulate the incoming RF signal.... I first noticed this effect when I turned an RX into a TX and finally removed the said invertor and fitted a battery that lasts over a year..... It seems that both Electric and Magnetic modulation of the signal were taking place...

It can be reduced but I found it difficult.

My answer was I used a pure DC source....

Decoupling never worked...

From an EMC point of view INVERTORS spell trouble.... G3RFL