[ARC5] T22 transmitter

[J Mcvey]

 The ARC-5 transmitters were originally designed to load into "short antennas" which are low impedance and capacitive.
The spec was 5 to 12 ohms resistance with capacitive reactance of up to around 500 ohms, which was to be "tuned out" with the roller inductor.
Here is the absolute min/max spec :



As Dave says, You can't just hook it up to a 50 ohm cable. 
For the 40 meter transmitter, I use the the 50pf vacuum cap in the antenna switch in series with the antenna connection.
I also use a 4:1 unun with the lo Z side on the antenna termininal. As long as the impedance presented by the cable is around 50 ohms or less. ( antenna less than quarter wave high) . It would be better if I used a 9:1, but haven't got around to it, because sometimes the antenna impedance I use may be greater than 50 ohms which puts it "out of range".
Your mileage may vary...

    On Friday, February 7, 2020, 7:42:17 AM EST, David Stinson <arc5 at ix.netcom.com> wrote:  
 
 Good Morning, Peter.
I believe the work has been done, but I don't remember where
may have seen it.  Frankly, I consider it "over-thinking the problem."
I've run the rigs into spectrum analysers using the series-cap
and found them very clean.  I don't think going to a more complex
solution will yield a meaningful improvement.
However- "each to his own" of course.

There is an active, long-standing "ARC-5" email reflector
at arc5 at mailman.qth.net with some excellent people.
For a broader milradio group, there are:

milsurplus at mailman.qth.net
MMRCG at groups.io

GL OM ES 73 DE Dave AB5S

On 2/5/2020 9:35 AM, Peter Bertini wrote:
> Hello Dave
>
> Has anyone ever come up with a more precise estimate for the T22 
> transmitter antenna impedance?
>
> I have one that looks like it just left the factory, and I intend to 
> get it on the air using you suggestions
> to keep it original.  It is an extremely nice black wrinkle painted 
> original,  with a lot of red factory labels.
> I have to research its age and lineage.
>
> I've read the advice concerning a series cap to cancel the rotary 
> inductor and link inductance... however
> I suspect it would also be easy to tack in two high voltage micas to 
> convert the rotary inductor into
> a Pi matching network, which should give a better matching range and 
> better harmonic suppression.
> The caps could be easily removed by a purist in the future without 
> affecting its value as an artifact.
>
> I am also looking for parts from junkers to restore several other 
> transmitters and receivers, are they any
> groups that cater to ARC-5 fanatics?
>
> Any thoughts?
>
> Peter W1BR
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