[ARC5] ARC-5 antenna match

[Christopher Bowne]

Neil - what Ken is describing is exactly what I was describing!




________________________________
 From: Neil <neilb at ihug.co.nz>
To: kgordon2006 at frontier.com; arc5 <arc5 at mailman.qth.net> 
Sent: Monday, July 29, 2013 4:44 AM
Subject: Re: [ARC5] ARC-5 antenna match
 

From: Kenneth G. Gordon
>> An antenna tuner can match a 50 ohm transmitter to a wide range
>> of antenna impedances.
>> I got to wondering whether one could be connected backwards to
>> match the unknown output impedance of an ARC-5 transmitter to
>> a 50 ohm antenna.
> 
> Of course it can. I used this method many years ago to build what one could,
> I suppose, call a very simple antenna coupler.
> 
> My reasoning at the time was that a parallel-tuned circuit with one end
> grounded is essentially a wide-range impedance auto-transformer, with the
> high-impedance end being at the "top", i.e., the end opposite "ground".
> 
> Therefore, one should be able to find a point on the coil, somewhere, that
> matched fairly closely any impedance between "high" and "zero".
> 
> Tapping the transmitter in at some point and the antenna in at another point
> would then result in a proper "match" to both.
> 
> In practice this worked very well, although it took some experimentation to
> get the best results.
> 
> Using a coil with as high "Q" (read, "lowest possible ohmic resistance") as
> possible, in combination with a fairly high value of tuning capacitor of a good
> design would result in an "antenna coupler" of fairly wide range, covering
> something like a 2:1 frequency range, at least.
> 
> My favorite such unit used a roller coil from a defunct Command transmitter,
> and an old, but very well-built, BC tuning capacitor. Taps would always be
> made between the "roller" and the ground end, the "roller" determining the
> basic frequency range over which the "coupler" would be used.
> 
> I also sometimes used a simple two-turn link around the "ground end" of the
> roller coil in lieu of a tap for the antenna IFF I was using a 50 ohm antenna.
> Otherwise, a second tap was used for the antenna.


Is this a high quality parallel tuned circuit, with the antenna coax connected
between ground (braid) and a tap on the coil, and the ARC-5 output connected
between ground (chassis) and a lower tap? Sounds like it could work well.

73 de Neil ZL1ANM

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