Cecil Moore wrote:
John Ferrell wrote:
Will the Auto tuner (SGC-237) that claims to match any wire greater
than 28 feet long really do it?

I once forgot to attach my bugcatcher so my SG-230
tuned a single four foot bottom section and reported
finding a match on 75m. The question is not will it
find a match but will it put any power into the antenna
at that "match" point - or is the tuner itself just a
dummy load?

That's precisely the point. If you wanted to match a 30ft whip on the
lower bands, and didn't have a tuner, you would be thinking about large
air-wound base loading coils.

The small inductors inside amateur auto-tuners are nothing like that
standard of construction, so the losses inside the tuner will be higher.
As Cecil says, when a tuner is forced into a tough situation, its 'load'
impedance may consist mostly of internal losses... and an auto-tuner is
perfectly capable of matching that.

One of my prized possessions is a Racal military auto-tuner that is
rated to handle 1kW continuously into a 30ft whip at 2MHz. Sure enough,
it contains some very large air-wound inductors, with the kind of high-Q
construction that you'd expect to see at the base of a mobile whip.

A really good amateur project would be to combine the smart controller
of a modern auto-ATU with your own individual collection of large
inductors, capacitors and relays. However, it would take some guts to
buy an auto-tuner, remove all the undersized RF components, measure
their inductances and capacitances, and then throw them away!


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek