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Old 3rd Apr 2020, 5:32 pm   #1
Wendymott
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Join Date: Jun 2013
Location: Huddersfield, West Yorkshire, UK.
Posts: 1,783
Default 6 metre 4 pole filter

Hi peeps.
Just an interesting bit of info... well to me anyway..

Doing some prep work on a VHF Triband Tranceiver.. I like to make modules I have not made or tested before....

The 6 metre front end filter was first..At 2 Mhz bandwidth, I chose 4 X Ind and 4 X caps... the inductors were suitably tapped to match the analyser.

In lashup mode.. all seemed well.. a reasonable flat ish top ...however looking at other circuits I decided to use a Double gate BF96 fet, to provide a bit of gain and AGC control.. Thus feeding the fet gate directly from the top of L4, I was getting a bit of very peaky responses, thus setting up was... difficult.. I played with various coil spacings and coupling, some were better than others, and I had no room or inclination to put screens between the coils..... so I hit on damping the "Q" of each coil.. I tried 33K at first and it was a much improved situation...finally 22K was chosen. Now I know its not perfect.. see photo..but in the final version, final tweeking should be ok.
There will be outer screening in the finished model
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Should get out more.

Regards
Wendy G8BZY
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