Shielded Filter Boards

I have been working on a few different things of late. One of the major ones has been to design some plugin filter boards that I can add shielding cans to. There are 2 different xtal filter IF boards, one using binocular inductors for impedance matching and the other using LC low pass filter matching. The latter is more an experiment to see if it is feasible to get a good passband ripple and impedance match using off the shelf SMD inductors and caps. Its easier to solder in 4 parts than wind inductors.

The other filter is a bandpass filter for a receiver. Again using SMD components rather than winding toriods. In simulation using a Q of 60 for the inductors the losses were acceptable. How they will go in practice is another thing. Worst case scenario is i add a MMIC amp onto the board and add some gain before the filter losses to make up the difference. My hand wound filters of the same topology had 1db loss in them. 2 or 3db loss using off the shelf components would be probably quite acceptable.

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One thought on “Shielded Filter Boards

  1. Make up the gain after the filter, not before.

    Putting it before just increases the level of everything you are trying to get rid of whereas putting it after means you are only increasing the level of the bit you want.

    Also less chance of leakage around the filter components if the signal level is lower.

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