Apologies again for railroading John's thread.
Stuart I only partially agree.
As long as you are not running high power, then yes you are correct.
You can use a good 4:1 balun and a T-match.
Of course that same balun and the Model 238 is even better because it will
have less loss.
However, when you are running high power, say 1KW, you have a much higher
chance of having RF in the shack with the Balun and T-box then you do when
running it through a good high power symmetrical matchbox.
I have been running open wire for about 48 years now, in at least 50
different locations.
I usually would have two open wire fed antennas, one vertically polarized
and one horizontally polarized.
I only had one high power symmetrical matchbox, the other had to use the
T-Box.
Regardless of which antenna I was using, whichever was going through the
T-Box would often have problems with RF in the shack on one or more bands.
I usually could find a way to cure it.
Sometimes a simple RF choke (toroids over the coax) would solve it.
Sometimes I would lay down a quarterwave counterpoise for the band that was
causing trouble.
Sometimes both.
***Before anyone jumps on me with "proper grounding", be aware that many
times my shack was on the 3rd floor or 5th floor of a large building.
This was not a onetime scenario.
I have had it happen several times at several different locations.
Sometimes it was so bad that the Omni VI would shut down and I would have to
power it and the power supply down.
Eventually I managed to find a second high power symmetrical matchbox.
Paid BIG BUCKS for it, but the problems were gone forever.
Can't blame the matchbox either.
I tried several different matchboxes, including the Palstar 4k.
Running 100w you shouldn't have these problems.
In fact running 400 or 500w you rarely see this problem.
It kicks in at higher power levels.
For 40m (my favorite band, so of course the one where I most often had
problems), I found 13 ft. of extra feedline to be the magical solution for
cases that it wouldn't find a match. Twice that for 80m.
I prefer open wire over all other solutions, but I must say that in this new
world where you change bands with a mouse click, tuning a matchbox is not
cool. Maybe I'm getting old and lazy, but I really enjoyed running the
Eagle in CQWW together with my OCF Dipole. I never had to tune anything.
The Eagle's ATU remembered when and where it had to be and everything just
worked at the click of a mouse. Now that's cool.
BTW for the balun used with the t-box most of the time was a RadioWorks
Remote Balun. Tried others too. I won't rule out that a better balun might
have helped. I can only say for sure that with a symmetrical tuner you
don't even have these problems!
For low power and openwire applications, I now run the MFJ-954B.
Been doing so for about 8 years. Ever since it came out.
I have found it totally superior to the old Johnson Viking when it comes to
matching all bands without having to add extra feedline. The only thing I
have found to be better is the Annecke 200w Symmetrical Koppler, but they
are rare here and practically non-existent in USA.
ONE THING I WOULD LIKE TO POINT OUT HERE is that the TEN-TEC transceivers,
as long as I can remember, have been able to run full power into an SWR of
3:1 without folding back power.
This means if you have an antenna like my OCF which has less than perfect
SWR, there is no need to use your rig's ATU. Simply pump power into it and
forget it. I only needed the ATU on 15m. Ran the other 4 bands without any
Tuner. The Eagle never got warm.
73
Rick
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Stuart Rohre
Sent: Wednesday, November 30, 2011 9:13 PM
To: tentec@contesting.com
Subject: Re: [TenTec] Jupiter Autotuner upgrade?
excellent discussion Rick for John's query on tuners for a G5RV
Technically, the G5RV was a low SWR on 20m due to its design. Users
have found that sometimes it also is a good match at 40m, but usuallly
no better than 3:1 at 15m, and of course it is short and capacitive
reactive at 80m.
The length of feeder can make a big difference in matching to any
antenna, and can be changed longer or shorter in small increments of 5
or 10 feet to effect a match if the original length is a problem to
match on a given band.
I built a variant of the G5RV, the ZS6BKW 92 foot doublet, with 40 feet
of ladder line before switching to coax (50 ohms). It was better than
1.5:1 on 20, 40, but 3:1 on 15m, without a tuner.
You actually can run ladder line all the way to the shack and match and
tune it appropriately. While a balanced tuner is nice, you can use an
efficient Van Gorden or similar external 4:1 balun on a T Tuner, the
most common commercial tuner circuit, and effect very good balanced
antenna work with Double Zepps and other doublets or dipoles.
If ever you have matching problems with a given tuner, add or subtract 5
or 10 feet of line to incrementally find the optimum feeder to work that
band.
Most built in tuners in rigs today are L match circuits, one less
component than Tee circuits. It is desirable to have switching of the
capacitor to ground from one end of the inductor to the other, to
provide for either a step up of impedance or step down. Of couser with
some L tuners, you can simply swap input and output coax connectors, and
use a coax to binding post adapter if mating to a balanced line.
While purists will use a double L network to balance things, often the
simple L, may work adequately into the balanced line.
-Stuart Rohre
K5KVH
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