[ARC5] ER ARC-2 & Antenna Matching

[J Mcvey]

I can see how that would work also, in fact, I used to load the lo-Z transmitters that way. The L-C will form an "L section" which will perform impedance transformation.
I like the series caps and transformer because there is less exposed hardware and I use the stock  front panel to effect the tuning. 
 

    On Tuesday, May 8, 2018, 12:39:44 PM EDT, Rich Post <kb8tad at gmail.com> wrote:  
 
 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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