[ARC5] SCR-274N Antenna Matching

[Dennis Monticelli]

Just to be more clear regarding my earlier email, the rollerductor is
retained and set at 23 on the scale (approx half scale).  The changes do
not interrupt any existing connections and can be very easily reversed.
 Leaving the rollerductor out of the network is not good for reasons of
originality and also harmonic reduction. Using too little roller inductance
will compromise harmonics as well.

Again, I am not proposing my scheme over any of the other proven
techniques.  I like it because it is simple and it further reduces higher
order harmonics because of the shunt capacitor.   I have looked at the
output of the T-22 on a spectrum analyzer and some extra harmonic reduction
is good practice if one wishes to meet current FCC specifications.  In
anticipation of getting blasted for denigrating the purity of the original
design, the ARC-5 used in its original state is reasonably pure and more
than good enough for it's wartime purpose.  The ARC-5 designers did a good
job.  It just could use a bit of help with current harmonic regs.  Simply
passing the output through your regular station antenna tuner is usually
plenty enough assistance.

Dennis AE6C




On Fri, Aug 22, 2014 at 10:41 AM, Dennis DuValll via ARC5 <
arc5 at mailman.qth.net> wrote:

>
> This seems to be a perennial discussion topic on this thread.    In my
> LONG term experience (60+ years) with these little beasts a simple series
> cap is sufficient for matching a 50/75 ohm load, 100pf for 80/75 and 50pf
> for 40M.  Cut in the variable link to about 25 %, peak the dipped PA
> current with the roller inductor and then finally adjust the link to the
> desired (dipped) plate current.  Also  a good idea to add a short shaft
> extension to the PA padder cap out through the access opening on the side
> of the chassis to facilitate keeping  the PA properly dipped.  Also, using
> the same capacitor values an "L" network can be formed with the roller
> inductor which provides a fine match into a half-wave end fed wire.
>
> In the recent thread the use of series caps along with an UNUN is
> described and, alternately, a series cap along with a shunt cap to ground.
> Apparently the roller inductor is not included in either circuit
> arrangements?  Not clearly stated……  Also, don't understand the fascination
> with UNUNs and their toroidal relatives.
>
> Enuf...
>
> Dennis D.  W7QHO
> Glendale, CA
>
>
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