Again, to piggy-back Tom, let me stress that it is always a bad idea to use
a tuner's built-in balun at anything near its rated power limit. As a rule
of thumb, I use about 20 to 30 percent (although I try not to use them at
all). The problem is, these things must be kept small to fit inside the
cabinet and they don't get much air in there either. USE AN EXTERNAL BALUN
(if you use a balun at all).
Bob, K4TAX, recently described (here on the reflector) a super balun made
entirely of coax. Use something like that.
73
Rick
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Tommy
Sent: Tuesday, July 19, 2005 12:39 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Tuner for Centurion to balanced antenna
At Tuesday 02:28 AM 7/19/2005, you wrote:
>Thanks Tommy...can you get the 80 meter dipole to match all bands,
>160-10, perhaps by carefully selecting feed length? Have you
>noticed if you have big nulls or spotty coverage on the higher (17,
>15, 12, and 10 meter) bands, as predicted by theory? Is your
>antenna in an inverted V fashion so that it nulls out some of these
>narrow lobes on higher frequencies? Yes, the expense of high power
>balanced tuners seems to be out of my range right now, so figured
>the 238B was about my limit of what I think I could do. But, you
>say you use 1.5 KW to a KW Matchbox? Didn't think they could handle
>it. Also heard the range was not great in the matchbox. Being an old
>unit, will it match on any of the WARC bands? I know the Ten Tec
>238B tuner is a good one and is supposed to do balanced lines, but
>with the internal balun, I am a little afraid to buy it and have it
>get awfully hot with big mismatches. Thanks for all the useful info!
>73, Greg, N6GK -----Original Message-----
No I can't. But only because my Johnson match box does not cover
either 160m nor 30m, without some mods to it. As for null's, actually
I have not noticed a problem with that. For instance the 80m dipole
wires are pointed toward you, however during something like the SS
contest, I can pretty easily work into W6 and W7 land on 80m, which,
by theory I should really not be able to do.
Hey, have some respect for 'old'!! I'm old too! The nice thing about
the Match Box is that it was designed specifically to work with open
wire feeders and it's pretty much a standard matching unit to which
others are compared. With my dipole I can successfully work 80, 40,
20,15,12, and 10 meters. The match box does not cover 10 MHz nor 1.8
MHz. The Johnson Match Box was rated at 1 KW AM modulated power
handling capability. Once when testing my Titan 3, I had coax from
the match box to the dummy load and got up to 2.4 KW into the dummy
load, before I chicken out. The Johnson 250 Watt match box, I have
heard, but never done it myself, will handle over a KW, key down.
Yep, the Ten Tec 238 series tuners are very good. If I were using
coax, that certainly is one of the tuners I would want on my desk.
Just be careful if you use it with open wire feeders and 1200 watts,
for heating up the balun. I would buy a cheap RS digital themometer
with the remote sensor and RTV it to the balun, just to keep an eye
on the balun, if the temp goes up, just drop the power output!
Bed time....!
73,
Tommy - W4BQF
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