[ARC5] ER ARC-2 & Antenna Matching

[Rich Post]

Hi Guys,

I'm with Jeep on this one for my 80 meter mostly stock SCR-274
transmitter.  In the past always used a parallel variable broadcast cap for
loading to a 50 ohm load.  Parallel keeps the cap frame cold.   For my
latest, after some experimentation with a variable cap, I added a 680 pF
dipped mica cap in parallel with the antenna and ground directly at the
antenna terminal.  The dummy bulb loaded properly and I could peak the
loading using the stock roller inductor.  I could also peak it readily into
a 50 ohm dummy load.

Here's a pic with the 60 watt bulb nearly overwhelming the camera flash.
Power supply shown is a Heath HP-20 with separate screen and oscillator
sources fed off the 300 volt side but regulated with a couple of
high-voltage N-channel MOSFETS recycled from computer power supplies and
mounted on a heat sink inside the HP-20 gated by a couple of zeners.  The
680 pF is clearly visible in the pic.  (And the little cap did not supply
any warmth for the shack  ;-)

<https://people.ohio.edu/postr/bapix/80meterARC-5.JPG>

Did similar with a 40 meter ARC-5 but later got lazy and just used an MFJ
tuner.
73 de Rich KB8TAD

On Tue, May 8, 2018 at 8:15 AM, David Stinson <arc5 at ix.netcom.com> wrote:

> Saw ER's latest issue with that cool ARC-2/ARC-5
> combination.  The author (our very own Jeep Platt)
> speaks of using 1000 pFd ( I assume between the
> ANT post and ground) to match a 50-Ohm load on 80
> Mtrs.  I use 100 pFd in series with the 50-Ohm
> load and get full output.  I'm not trying to
> criticize someone else's solution, and I know
> we've talked about this before; just want to
> understand- would think that 1000 pFd to ground
> would eat a lot of power in circulating currents,
> just like matching an electrically short vertical
> by putting a big cap at the bottom.  It will tune
> it, but since the majority of the RF currents are
> down near the ground, they contribute nearly
> nothing to the radiation resistance of the overall
> system.  A series cap doesn't divide the RF
> currents this way.  Some folks- and I assume with
> good, sound reasons- prefer the cap to ground
> method.  What am I missing here?
> Thanks,
> Dave S.
>
>
>
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