I do have a small Johnson Matchbox, but it doesn't have the versatility
needed for my wire antennas, so I've built my own tuners. My big tuner
(built long before I owned an E. F. Johnson tuner) is overbuilt with a
huge coil that's too long with a link in the center. I use a fixed link
with a variable capacitor, probably 300 pf maximum, in series with the
link. I use a pair of similar capacitors for the output side equipped
with alligator clips so I can pick turns on the coil and capacitor
connections either series for low impedance or parallel for high
impedance. The link and the output coil do the balancing, I don't force
balance by grounding the center of the output coil, though that often works.
For 21 MHz and up, my tuners have been single band with a dual section
capacitor that forces balance by grounding the frame of the capacitor.
Then I tap the feed line to the turns where it matches. And use a
variable link instead of the series capacitor on a fixed link.
These tuner circuits are discussed in my 2002 ARRL Handbook long about
figure 19-10. Construction is illustrated in the 17th ARRL Antenna
Handbook on page 25-7. For the loads described they all work, some
better for some loads than others.
MFJ now makes coil stock, that we used to get from B&W. And variable
capacitors. Mouser carries ceramic wafer rotary switches as does RF
Parts. RF parts has them in PA sizes for good money. Not cheap.
These circuits have been working for 70 or 80 years.
Sometimes when a tuner doesn't have enough reactance or impedance range,
we can adjust outside the tuner. Like adding more shunt C or a series
coil on the LF end, changing the feed line length as much as an eighth
of a wavelength, or for a very low impedance feed point using a ferrite
core conventional transformer. These solutions will tend to be specific
to one antenna on one band.
I'm no fan of tuning a balanced line through a balun. I lost faith in
that long ago when I tuned up on 10m and didn't hear signals, and when I
unhooked the antenna the match into the tuner didn't change. I'd
resonated the balun, not the antenna. A concept that I like better, but
haven't done it yet is to float the tuner and feed the tuner through a
balun so the balun always sees 50 ohms or 200 ohms depending on the
tuner design and without significant reactance. I'm thinking the MFJ
remote tuner that gets its power through the coax might be good for
that, but I've not yet tried it.
73, Jerry, K0CQ
On 1/14/2011 8:16 AM, Ed Purvis wrote:
I need the definition and model number of a "good tuner".Hopefully, something
without a balun. Maybe somethingalong the lines of the K1JJ homebrew tuner also??
tnx, Ed
IF AT FIRST YOU DON'T SUCCEED, SKY DIVING'S NOT FOR YOU.
--- On Thu, 1/13/11, Dr. Gerald N. Johnson<geraldj@weather.net> wrote:
From: Dr. Gerald N. Johnson<geraldj@weather.net>
Subject: Re: [TenTec] ant
To: tentec@contesting.com
Date: Thursday, January 13, 2011, 4:41 PM
And 6m and 2m quite well. And probably 160 with a good tuner.
73, Jerry, K0CQ
On 1/13/2011 3:13 PM, ROD wrote:
If you don’t work 160 then a good ant. is the double extended zepp 83 ft on
each side for a total 166 ft feed with 450 or 300 ohm ladder line. with a good tuner
you can work 80 40 20 15 12 17 10 meters. the hams of yester year use this antenna.
73 Rod Dewald W3KRQ
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