[ARC5] QST articles.

[Bob Macklin]

There is NO HARMONIC suppression built into ARC-5 transmitters!

Bob Macklin
K5MYJ
Kent (Seattle), Wa,
"Real Radios Glow in the Dark"

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at verizon.net>
To: "Ian Wilson" <ianmwilson73 at gmail.com>; <ARC5 at mailman.qth.net>
Sent: Sunday, December 14, 2008 4:28 PM
Subject: Re: [ARC5] QST articles.


> On 14 Dec 2008 at 15:37, Ian Wilson wrote:
> 
> > Not if you want any decent power output. You need to transform the
> > real part of the antenna down to a few ohm to match the optimum load
> > that the ARC-5 TX wants to see.
> 
> Correct. Furthermore, by doing as Bob suggests, and as 
> many other hams did, you also completely defeat any 
> harmonic suppression built into the rig.
> 
> > The best way to do this on 40m I have found is to use a parallel
> > capacitor of around 1200pF.
> 
> Yes. That WILL work.
> 
> However, the very BEST method, if you wish to feed a 50 
> ohm load (like a modern antenna coupler) is to use a three-
> element "Tee" matching section.
> 
> The left arm of the Tee being part of the normal ARC-5 
> loading coil, the middle  (vertical) arm being a capacitor to 
> ground from the antenna connector, and the remaining 
> (right) arm of the Tee being another capacitor in series with 
> the antenna connector and the antenna.
> 
> Values can be easily calculated using Zin of 5 ohms, and 
> Zout of 50 ohms, or a 1:10 transformation.
> 
> I will post the necessary formulae asap.
> 
> As I remember what I recently read concerning this, on 80 
> meters, the inducance end required about 7 turns on the 
> normal ARC-5 loading coil, a 680 PFD cap to ground from 
> the antenna connector, and a 365 PFD cap to the antenna.
> 
> But don't hold me to those values. My memory isn't that 
> good any more. (Obviously!)
> 
> I only mention those to illustrate the range of values 
> expected.
> 
> Then you set the link to about 1/2 open.
> 
> Power output was somewhat over 30 watts at 450 VDC on 
> the plates of the 1625s.
> 
> Ian's method will work fairly well, and is, in my opinion, a 
> version of the Tee matching network, the series 
> capacitance of the antenna comprising the third leg.
> 
> HIs method would probably work best with an end-fed wire 
> antenna, or an antenna that exhibited more than 50 ohms 
> impedance.
> 
> Ken Gordon W7EKB
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