[AMRadio] High-power tuners

A.R.S. - W5AMI ars.w5ami at gmail.com
Thu Dec 7 21:38:53 EST 2006


I don't have a BC tx, but my rig would compare in regard tuner
requirements.  I home brewed a link coupled tuner, and think that's
the only way to go for a big power AM tuner to open feed line.  I got
a very large rf coil with rotating link off epay several years ago,
along with a split stator air variable of about 250pf per section and
probably 7+kv rating.  Very simple to build if you can find or make
the parts.  I've tested the tuner into a makeshift load (dummy) of
about 200 ohms with almost 3KW and the coil did nothing but get a
little warm after a minute or so.

Brian / w5ami

On 12/7/06, John Lawson <jpl15 at panix.com> wrote:
>    I'll be dragging an RCA BTA-1MX broadcast transmitter back to KB6SCO
> next weekend. (Was going to try this weekend, but schedules and weather
> prevent...)
>    And I'll be primarily QRV (QRO!) on the AM Window of 80M.
>    I have a 480' square loop of good 14ga copperclad wire strung around the
> fence at the rear of my property - the feedline is 450-ohm ladderline at
> the point closest to the shack. It's 5' off the ground on average, one leg
> of about 50 feet is at 7'.  It's a quasi-NVIS, or "RF Fountain" if you
> will.
>    And before the "Why don't you..." comments even get started - I can't do
> anything else in the QTH I'm in now - the Antenna Configuration will not
> change until I move...
>     Currently I use an Ameritron ATR-15 tuner, using the balanced outputs
> (through an MFJ crossed-needle balanced ammeter) and driven by my faithful
> Valiant.  On any part of 80, I can tune 'er down to 1.1:1 - and have many
> successful QSOs with good signal reports - so the System appears to be
> working.
>    NOW, THEREFORE:  I would like to use the RCA and yet do as little damage
> as possible to the Rig, the Fence, and my Nieghborhood Relations.  I have
> a plan in mind to build a fixed-bandwidth tuner installed at the feedpoint
> of the Loop - and just run good coax out to it - from where the RCA will
> be situated this is about 30'.  I also have a dual-rolling-inductor tuner
> which was built by someone who makes them 'to order' - still pretty much a
> homebrew job - it is supposed to handle 2KW easily - and has a coax
> solenoid for a balun.
>    What are you QRO-types' experiences with tuners, antennae, and higher
> powers?  Especially if anyone is running a b'cast rig thru a homebrew or
> commercial (or military?) tuner -  I'd be curious as to pros/cons -
> likes/dislikes - horror stories, etc.
>    Cheers and Best of the Season
> John
> DM09fg
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