[ARC5] Re: TX relay for ARC-5

[David Stinson]

----- Original Message ----- 
From: "Doug Forbes" <dougforbes at dslextreme.com>
Subject: [ARC5] TX relay for ARC-5

>.... I would like to put it back the way it was and need the relay that
> mounts on the underside right of the chassis. 

Please send your address.  I have a few around here.
Need any other parts?

> If you folks know of a way of getting chirp-free operation 
>...without the relay..

No way I know.
Get the relay.  Adjust the contacts so the oscillator comes on 
before the 1625 cathodes are grounded.

> as well as a way to use the unit without a tuner into a 50 ohm load...

Cheap and easy way: 
Put a 50 pF, 1000 volt NPO cap in series with the loading coil
and out to the antenna.  
Use NPO or similar kind that does not drift when heating, or 
you'll get some chirp.  Won't give 100% of full output, but will
be close and it's easy.

Better:
100 pF or so variable in series with the loading coil and 
out to the antenna.  Must be mounted isolated from ground, 
of course, and you'll have to deal with hand capacitance if you
want to get maximum "tweak."  

Best:
Wind a 4:1 "Unun" broadband transformer to transform
the low output impedance to around 50 ohms.
Make sure it's actually a good HF core; 
some of the red-painted "ham fest" cores have
turned out to be RFI dogs, at least here.
Use a large-enough core.  If it gets hot,
it's either too small and is saturating or 
is the wrong mix.

No credit to me; all this comes from the good folks
on the milradio and ARC5 forums.

73 Dave S.

P.S.: As with any MOPA rig, if anything changes the antenna loading,
it changes the load on the PA and, thus, on the oscillator.
If your antenna swings in the wind, your oscillator will swing with it.