[600MRG] Some experimenting with toroids vs hollow coils on 630m

[Dave Riley]

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


On 2/15/2023 9:51 PM, Neil Klagge 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
>
> My ham radio website: http://w0yse.webs.com/ <http://w0yse.webs.com/>
>
> My Faith website: http://neilsfaith.webs.com/ 
> <http://neilsfaith.webs.com/>
>
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