Hi Neil,
52 mix is for HF, otherwise too many turns for 630m but it will
work
75, 77 or F mix good for 630m Usually 75 mix used here and they
run cool
But if you need to get to VLF say 17.2 khz then there is J mix
Great for RX loop coupling down to 10 kc. else use a good audio
transformer..
Bottom line for me was to get rid of the base reactance with some
Z in series with the high Q air coil, then step that R down to 50
ohms for the rest of the trip..
Get rid of reactance @ feed point then transform down to coax via
transformer..
It took too many sacrificed IRF460s to come to these conclusions,
hi hi
Nano vna helped a lot too..
73s from Dave W1FRV ( looks like the band is out for the season
? )
Generally speaking he least amount of turns for the lowest frequency
The following is just my experience, not a scientific thesis 😉
These are the results of an experiment comparing a FT240-52 with a hollow cylindrical coil on the ouput of my 630m IRF510 FET power amplifier for 630m.
Transmitter output was 4.5w input to the toroid for this test, but there was only 2w left on the output of the toroid, going into the coax to the antenna. The KA7OEI-1 Northern Utah SDR was used during midday to decode my signal with that core. The results were worse by about 10 dB compared to when using the hollow PVC coil. The amplifier ran very warm with the toroid even though my fans were running full blast and even though the SWR was very low.
Using the same output power of the amplifier, the cylindrical coil got a 10 dB stronger report from the SDR. And, there was negligible heating of the amplifier. (I had similar results with an FT240-43 core the previous week).
The #52 core is less than 45% efficient whereas the PVC coil is about 83% efficient. The PVC coil wins!
Next, I experimented with the 52 core at the base of the antenna. I was able to get the SWR under 2.0 at the base of the antenna by adding or subtracting turns on the core. Inside the shack I could adjust the SWR to about 1.2 but the amplifier still ran hot when using the toroid and the reports back from the N. Utah SDR were weaker by about 7 dB.
My original coil at the base of the antenna works much better than the 52 core.
Hoping some will find this useful...
73*´¨)
¸.•´¸.•*´¨) ¸.•*¨)
(¸.•´ (¸.•` Neil , wØyse, DN41ah, North Ogden, Utah 84414
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