Re: LF: TXing WSPR/MF on an indoor loop, part 2

[Markus Vester <markusvester@aol.com>]

A little snapshot from the DL0AO LF/MF-grabber...

73, Markus


-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: So, 3. Feb. 2019 15:00
Betreff: Re: LF: TXing WSPR/MF on an indoor loop, part 2

...indeed! Since more than 72 hours i'm running the WSPR transmission in 25% duty cycle (each 8 minutes). First i tuned to 20 A antenna current and the temperature / antenna current changes were much smaller. But there was a certain click, or krrrrkkrt audible from the Cs. It was likely that there were indeed internal voltage breakthroughs, which were self-healing. Now after 3 days the current dropped again to 14 A, meaning that the capacity dropped, so the loop became detuned and so the RF current and voltages dropped to a level which is accepted by the capacitors.

So my conclusion is, the derating curves actually should be considered.

I wonder if the effect is still happening if one keeps the temperatures down at 25 C or even lower. When placing the capacitors in de-ionised iced water, it should be possible to keep the temperatures down, also in the internal of the capacitor.

But all in all this is not a good solution. Fortunately i have another antenna which is more efficient :-)

73, Stefan
...

dl0ao_mf-qrss_190203_2235.jpg
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