Art Unwin wrote:
On Nov 1, 12:34 pm, you wrote:
In article
,
Art Unwin wrote:



Browsing thru E bay I came across a 1kw
antenna tuner for sale from Cyprus.Now in my younger days I got hold
of one of these and intended to salvage a Icom AH2 to somehow make it
remote since I use Icom radios. After all there are only three motors
that have to be driven! Now I am retired I pulled my old one from
storage after seeing the same on E bay. Question is are there any
kits, salvage ideas out there that would get me going on this long
lost project?
I have never used a external tuner but this seems like a realistic
project to play with.
Of course if there is a unit out there that I can salvage a controller
that is all the better. There are very good photos of this particular
tuner on E bay but like mine it has no controller! I suppose I could
feed a 10 watt signal to it and control the motors by hand to tune but
I do like the idea of automation.
Regards
Art
It isn't the tuner hardware that is going to be a problem, as much as
designing the tuning algorithm that drives the hardware. Mark Johnson
did a very good job, reverse engineering the stuff that Bill Shield
brought west from Motorola Military back in the 70's for the SEA
Autotuners. SGC copied the SEA Firmware & Design enbank, for their
stuff. The best stuff, was the stuff Collins did for their Military
Autotuners. Starting from scratch is going to be a BIG design project.

My problem as far as I can see is that the control for the AH2 is that
the innards are transferable but it only controls two motors where as
my tuner has three.
I suppose I could just use two and not utelise the fine tune inductor.
Will sleep on it for a while and look at the AH4 version or in the
worst case fine tune by hand if necessary. I suspect the fine tune is
not really necessary in most cases other than satisfy the over
zealious swr users

If you can guarantee that the real part of the feed point impedance is
always higher or lower than your transmission line Z, then you can use
an L network, which only requires 2 adjustable components.

You see a lot of these sorts of schemes with physically short radiators,
where the Rfeed is always less than 50 ohms.

L networks have the nice property that there's only one setting that
"works" which is nice in an automated system. I think the usual scheme
is to spin the C pretty fast and slowly ramp the L, and then stop both
motors when the match is "good enough".

For relay based systems there are better algorithms for finding the best
match that take less time.