Hi,
I have a PCB with LNA connetcted to RF downconvertor at 1575MHz. Now I do not need this LNA. How do I short circuit this LNA. The input and output points are directly opposite. The board is a six layer board with FR4. Can I just use some capacitor to reduce the cabling or just use cabling?
You will also have to remove the first and last part of the circuit so that the amplifier is not in parallel with the transmission line. Also, connecting the input to the output will cause it to oscillate.
DO NOT short this device out with copper strips. The bias connnections are more likely to still be in place and you will damage the PSU. The capacitor shorting is by far the best method. Use a 47Pf cap to start with. The device cannot oscillae because it will be missing. you may have mis-matching and this could potentially cause ripple. Your conversion gain & NF may be affected depending on the signal level into the down convertor.
1. You should use some series capacitors or should remove biasing the LNA.
2. At about 1500 MHz a few millimeters of length of a 50 ohm strip will not cause any problem (as I guess your LNA is a matched one).