Hello Jan,
the coil that troubled me last night is the elevated loading coil. It is at the
top of the vertical section and its function is to increase the average current
through the vertical section, and thus the radiation resistance. As it is
hanging at the topload wire it causes some "sag" what is not so good. Therefore
the coil is contructed for minimal weight. It is wound on a plastic 1 liter
"yogourt box" with no additional protection of the wire. Advantage is it's
weight (only 190 gram for a 200uH coil with a Q of 180 !). Disadvantage is that
it detunes the antenna when wet, but as I do not transmit when raining (due to
arcing) and it dries very rapid up there, it is no real problem. But these
days the coil wss covered with a very thin ice layer that detuned the antenna
so I had t retune the loading coil at the base. During my QSO with Louis I
noticed that the antennacurrent was going down. When I pointed the flashlight
at the loading coil I saw water dripping of, so the ice was melting (despite an
outside temp of -5C).
Reactance of the 200uH coil at 500kHz is 628 Ohm. At a Q of 180 the loss
resistance is 3.5 Ohm. Last night I was running 200W out, resulting in an
antenna current of 2.2A. The heat production in the loading coil was thus 17W
during "key down", so about 8W average during my transmission. And probably
the ice lowered the Q, so it there be even more loss. Anyway, it was sufficient
melt the ice.
73, Rik ON7YD
________________________________________
Van: [email protected] [[email protected]]
namens pa3abk [[email protected]]
Verzonden: woensdag 1 december 2010 0:53
Aan: [email protected]
Onderwerp: Re: LF: MF_Beacon DI2AF is running in WSPR_Mode
Thanks Rik
Some time ago I did the TS440 mod for removing the 20dB att, but
restored the original situation immediately.
It's useless... So much shit coming in.
Heard yr QSO this eve with Louis
What a luxery problem... Your antenna coil is producing so much heat it
melt the snow!
Anyway your sigs were vy strong here.
Jan/pa3abk
Op 30-11-2010 9:07, Rik Strobbe schreef:
>
> /I'm using a TS440 which can't switch off the AGC by nature. So
> reduced the gain and turned up the LF gain to get a proper feed for
> the WSPR decoder./
>
> //
>
> Jan,
>
> I am using a Kenwood TS440 too. I find it a very good RX, both on
> 137kHz as 500kHz.
>
> It has by default a 20dB attenuator activated between 500kHz and
> 1.6MHz. But so far I found no need to remove that, as I am using the
> TX antenna (lazy-L, 11m high, 25m long) also for receiving.
>
> For receiving DI2AN's WSPR I used the 10dB extra attenuator and then
> reduced RF gain for a stable s-meter. The soundcard is connected to
> the back audio out connector as, the level there is independent of the
> LF gain.
>
> 73, Rik ON7YD - OR7T
>
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