Topband: BC filter

[Rudy Severns]

The filter I used is made by Industrial Communications Engineers (ICE),
model 402.

    As for the effect of the filter on the SWR measurement.  I checked that
by measuring the SWR of a dummy load with and without the filter.  There was
no detectable effect above 1.8 MHz with the MFJ-249.  But as I went down to
1.75 MHz or so then you could see the effect coming in.

    The question is a fair one however, and if I get a moment in the next
few days I will pop the filter on my HP 3577A network analyzer and make a
definitive measurement.

    Because of the large BC signals which can appear on the antenna, there
is a measurement issue.  The GR1601 is a good way to go if you use a narrow
band detector.  Of course you need the bridge, a signal source and a
detector which is a bit busy but not that bad.  In my case I am end feeding
1/2 wave elements so I needed to measure impedances in the 6 kOhm range, a
bit much for the 1601.  I found that the Boonton/HP 250A RX meter was a
better choice.  It has the advantages of a tuned detector and being vacuum
tubes, uses large signals for the measurement.  The BC pickup didn't seem to
bother it all.

    More modern instruments like the HP4815A, etc, do seem to be affected so
beware!  That's the real message here.

73, Rudy N6LF