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Ferrite rings ? (1 reply)

6 months ago
Mw7ofs 6 months ago

I've got 4x fair-rite 43 and 4x 240 31 . Where would you recommend I install them and how many turns/windings? Inside the shack I'll have the radio , a comet cf30mr , an mfj 993b and the power supply . Outside will be an endfed antenna with a 49:1 matching unit by rfcomms. Also at some point I'll be experimenting with verticals .



3 months ago
M7CKL 3 months ago

I'm not familiar with low pass filter cf30mr.

I put 9 turns of my HF antenna cable on an FT240-31 outside the shack. It is on the wall in a grey box - bought from Screwfix. Endfed has a counterpoise that is 1/20 of lowest band e.g. 80m = 4m - it is on the other side of the antenna on 49:1 and dangles down but does not touch the ground.

NB using an earth to ground isn't always effective - it can appear as an inductance and an earth rod may not provide the low impedance depending upon ground (soil) and other factors.

I also put an FT240-31 with 6 turns on my PSU mains cable (L + N + E). I would have put 9 turns but I needed the additional length.

I also put an FT240-31 with 9 turns on the output side of the PSU - both the red and black wires.

I haven't needed an FT240-43 so far because the FT240-31 covers 80m-6m OK.

PSU is a switched mode version. It has a mains earth for the metal case and the common (black) wire is also earthed. The RF earth terminal of the radio is connected with 10mm cable to a 4 foot copper earth rod. RF earth is connected through to mains earth - not ideal but seems to work OK.

I also have a lightening arrestor for the HF antenna - also connected to the earth cable to the earth rod. For UHF/VHF I'm in the process of installing a second lightening arrestor. Better than nothing and bleeds off static but a direct hit would probably destroy the cables and/or some equipment anyway.


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