Jim es Co
The highest Q coils I have seen are self supporting encased in a helium
container and the Q specified was only in a few hundred. What sort of coil
construction yields 4000 and above ?
I have yet to encounter such a specimen
mal/g3kev
----- Original Message -----
From: "James Moritz" <[email protected]>
To: <[email protected]>
Sent: Sunday, December 18, 2011 10:58 AM
Subject: LF: Re: Re: TX system at DK7FC, schematic
> Dear Mal, LF Group,
>
> > I can see you resonate your 3mH coild with a motor driven variometer but
> > how
> > do you match this to exactly 50 ohmz for a SWR of 1:1 to the TX
> > I can see your coil and transformer secondary are in series to earth
but
> > no
> > adjustment for matching.
>
> Essentially the same arrangement is in use here. The transformer ratio is
> adjusted to match the antenna resistance to 50ohms.
>
> A Q of 1000 is typical for a coil of this size wound using Litz wire. You
> might increase that somewhat by optimising length, diameter, winding pitch
> etc. For something big like the Balboa loading coil in Alex's mail, Q can
be
> considerably higher - Watt's "VLF Engineering" has data on this particular
> antenna system - the coil resistance at 25kHz is about 0.06ohms, and the
> reactance 225ohms, making the Q about 3800 - it might be higher at 136k,
> since reactance often increases faster than loss resistance as the
frequency
> goes up. Incidentally, I estimate L of the main loading coil about 1.3mH,
so
> GW0EZY would need the variometer in series as well ;-)
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
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