[Boatanchors] IF Filter testing...

[Barockteer@aol.com]

Testing filters (and IF transformers) isn't that difficult, assuming you have access to a calibrated RF generator and means of measuring low level RF signals. This could be done with a modern general coverage HF receiver, assuming it covers the passband of interest. (Getting down to 50 KC might be a bit tough, but most rigs go down to 100 KC). The receiver S-meter can be calibrated using a step attenuator. Or, you can use a substitution method to achieve the necessary measurement accuracy.

The hardest part is the requirement that the source and load impedance of the filter needs to be terminated in the proper impedance for the filter to perform nominally. Often, the source and load impedances are not know, such as for older Collins mechanical filters. Also, some filters rely on external reactances (capacitors) to tune them.

If you can test them 'in situ', in the equipment where they are used, then signal injection/measurement techniques can be used and the termination issue is taken care of by the rig itself.


The easiest way to do it is with a $20,000 network analyzer. However, it can be done with the kind of gear found in most ham shacks (once the termination impedance issue is addressed).

If there is interest, I would be willing to write up a sample testing procedure...


73,

Tony, K1KP