WW2
HF Filter, AP56152
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I believe I bought
this RF filter in 1961 after I'd built my first transmitter and
suffered from really bad TVI.
I don't think it was ever pressed
into service though as it couldn't easily match into a long wire
antenna and it's just been hanging around for years, lastly in
a rather damp caravan which is slowly returning to nature and
merging into the background.
I fitted a pair of PL259 sockets
in place of the dreadful old Pye coax plugs and removed the label
before rubbing down the case prior to repainting.
Of course, "AP" means
Admiralty Pattern and I'm reliably informed it was used in front
of the B28 (Marconi CR100) and the B40
series of receivers to eliminate RF interference originating
from ship-bourne equipments. |
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Opened up you'll see it
carries six stages of matching/filtering and employs beehive
trimmers each soldered into position. |
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Below is the finished
filter painted in matt black. The label says it was made in 1944. |
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Here is a set of pictures
taken from my spectrum analyser proving the filter was well designed
and has stood the test of time |
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The horizontal scale reads
0 to 60 MHz and the curve dives down from 30MHz and flattens
out at about 36MHz |
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I set the marker to roughly
the 3dB point which is 30.6MHz |
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Below is a scan from 0
to 500MHz... pretty good for a 70 year old piece of government
surplus kit |
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