Message-ID: <4F0DFFB1.8040509@iup.uni-heidelberg.de>
Date: Wed, 11 Jan 2012 22:31:29 +0100
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: Tuning inductance for 137kHz receive.
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Hi Martin,

Am 11.01.2012 21:44, schrieb Martin Evans:
> I use a decade inductance bridge to series tune my  (approximately) 
> 50m end-fed  inverted U wire for 137kHz.
>
> It uses 3mH - 2mH is too little, 4mH is too much. Obviously I need to 
> be able to vary this inductance rather more finely and I thought of 
> using a small variac (don't laugh!) as a variable inductance, 
> connecting one end, and the tap, in series with the wire.
>
> Anyone know what the "inductance per turn", or total inductance, of 
> such an animal might be?
The L will be much to high and the Q will be very low (=lossy). Also it 
has a high parsitic C and will have a self resonance below 137 kHz. So 
it rather acts like a capacitor.

BTW capacitor, this is what i suggest. Simply use the 2 mH and a small 
variable capacitor connected to the wire and GND. Then you can 
accurately adjust to LF.

Unfortunately i can't generate a reasonable test signal for you tonite 
but there are a lot of UK transmitting stations :-)


> Any idea if it would work?
Yes, NO.


73, GL, Stefan/DK7FC