[TenTec] Ten Tec 229 Tuner on 160M

[Dr. Gerald N. Johnson]

On Fri, 2007-12-07 at 11:40 -0600, Bob McGraw - K4TAX wrote:
> This is one of those topics that gets visited from time to time.  And as 
> always, there about as many opinions, ideas, experiences and preferences as 
> there are stars in the universe.
> 
> Wire, whatever length you have space to string up, fed in the center with 
> some balanced feedline direct to the tuner has always proven to be a good 
> working general purpose antenna.  Balanced feeds are not near as fussy as 
> many will technically profess.  I use both the 300 ohm and 450 ohm material, 
> {window line} which I obtain from Press at Wireman.  Whatever balance method 
> that exists in your tuner will likely be satisfactory.  Should your tuner 
> not provide a balanced output, then add a external balun of your choice. 
> I've used a W2FMI 4:1 balun rated at 10KW for my legal limit operation. I've 
> also used a Radio Works 1:1 current balun rated at 5 KW for my AM station. 
> Both seem to work equally well.  My favorite is "the ugly balun" as 
> described on Rich Measures website. http://www.somis.org/bbat.html
> 
> I only use coax fed antennas for those that are resonant frequency 
> applications.  Case and point, my 75M dipole, length cut to formula, and 
> coax fed shows a 1:1 SWR value at about 3950.  It covers some +/-50 KHz 
> {3900 - 4000} either side of that frequency with a 1.5:1 SWR or less.  The 
> radio and amp are very happy with this configuration and I typically don't 
> use the tuner on this antenna for operation in the upper end of the band. 
> Now should I decide to do some PSK-31 work down at the low end of the 75M 
> band, I switch in the tuner, twiddle a couple of knobs and everything is 
> happy and works.
> 
> For feeding the balanced lines/antennas the Tentec 238 does a very nice job.
> 
> Try it, you'll like it.
> 
> 73
> Bob, K4TAX

I've always disliked tuning a center fed wire through coax because when
the wire is a full wave long and the coax is at least a quarter wave,
the impedance at the low impedance spots on the line gets to be small.
The worst case if for full wave dipole about 1000 ohms, and a quarter or
three quarter wave point from the dipole in 50 ohm coax. That impedance
at that point gets to be 2.5 ohms. So the current for 100 watts is 6.3
amps which is a lot for RG-58, OK in RG-8.

The other problem is that some tuners (Johnson Matchbox for certain)
don't work with that low an impedance load.

I've learned in some cases to dislike tuning through a balun because if
the impedance at the balun is high the core is likely to be saturated by
the magnetization flux leading to lots of heat in the core and extra
harmonics. And on one such occasion, I found after tuning that unhooking
the feed line made no change in the input Z or match. The majority of
the input power was being dissipated in the tuner and the balun on its
rear panel. That 10 KW balun shouldn't be bothered much by core
saturation.

That being said, I'm finding that some tuners (that will tune an
unloaded mobile whip) will tune the low impedance from that full wave
dipole, and will radiate a signal. Except that last weekends ice storm
unhooked one side of my 80 meter inverted V from its fence post anchor
(thin nylon weak link wore through), I've been running it on 160 through
10 meters. Its feed line is RG-141 so its somewhat tolerant of heat and
weather.

While its not possible to be optimum sometimes to feed with balun or
with open wire line the lowered efficiency isn't absolute zero, it may
be 50% or 10%, but that's still good enough to be heard sometimes. It
may not be good enough to break a pile up until its been there for a
couple days.

Point is, getting on the air with something working partly is more fun
and effective than sitting and wishing the antenna was perfect.

I used to run an 80 meter double extended Zepp with tuned feeders from
through 2m, Worked many contacts on 6m and out to 350 miles on 2m. The
best feed line was open wire, it didn't get moved around in the wind as
much but that 18 gauge copperweld had a very short lifetime when coated
with ice and flexed. The top was made of 10 gauge copperweld telephone
wire. Good stuff but a bit stiff to work through the insulators.

73, Jerry, K0CQ