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I build some plasma generator stuff from time-to-time, some below
the 500kHz.
The attached core stack with a two-turn CT primary would be
perfectly fine at 50Vds and the transistors swinging the full
voltage in push-pull at 25 amps. I actually used a single core
like this in my IC751A and used a different binocular in the
driver output and my 751A it is perfect even at 100W. It runs just
like it did at HF.
It was like 10W and running hot with the stock ICOM cores. I can
get 10X the power now. :)
I can swap it to 52 material and with a few more turns but the
same ratio, or a deeper core window, have it work also.
61 is a too low on ui to be usable.
I sure wouldn't use a high ratio transformer like they use on HF
in a reactive load on LF. A short LF antenna has a ton of power
factor that needs correction. It would be way better to use a high
Q coil to match and correct the power factor all in one component.
73 Tom
Very interesting and thanks for posting. Seems a lot of amateurs are having great success using a 9:1 or 49:1 toroid to feed a random wire on HF. Or so they say, Tempted to give it a try but I don't have suitable cores in my junk box. Must be a matter of luck to get the length of the random wire just right.
73 John / VE7BDQ
On Wed, Feb 15, 2023 at 6:51 PM Neil Klagge <[email protected]> wrote:
______________________________________________________________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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