[TenTec] 229 and 238 tuners mod

[rick@dj0ip.de]

Rob is right.  
And we should also build or own cars because we can all build better cars
than what GM and Ford (etc.) are selling us.  ;-)

Rob, as perfectly correct as your email was, it is no longer a viable
solution for 90% of the hams out there today.  A couple of guys might
actually manage to find what they need at hamfests, but there aren't enough
components available to support the masses.

To categorically claim all Palstar and all MFJ matchboxes are bad is not
fair either.
They were designed for the kind of antennas most hams use today, not for the
openwire antennas of yesteryear.

In order to have a good match to an openwire fed antenna, you need two
things:
1). A means of matching
2). A means of managing the Common Mode Current (CMC) which sometimes can be
hefty.

The old Link-Coupled tuners Rob speaks of were great and inherently had an
advantage in coping with CMC.  But there are way now days to do it using
today's products.
It is only a huge challenge if you insist on doing it with 1500w.
It's all about choice of balun and where you physically locate it.

If you are running 500w or less, it's a piece of cake.

The built in baluns of most antenna tuners are totally worthless.
The only exceptions (and that just recently) are on the larger manual
matchboxes from MFJ.  They have finally switched to a 1:1 current balun with
multiple cores.
This is what is required for coping with severe cases of CMC.

As VK1OD writes, it is best to mount the 1:1 current balun external from the
tuner in a plastic box, away from any metal.

The recommendation for 4:1 balun (as the only balun) under any circumstances
is bad advice.  The balun should always be a 1:1 current balun.  Of course
if you have an older symmetrical matchbox (Johnson or Annecke) you don't
need any balun at all.

Using the 1:1 current balun does not prohibit also using a 4:1 balun as a
transformer, in addition to the 1:1, but it should only be switched in when
absolutely necessary.

For more detailed technical information on this, see my web page on tuner
baluns.
I have compiled a list of technical papers on this topic from W8JI, G3TXQ,
VK1OD, etc. 
Links to each of these is listed at the bottom of this page:
http://www.dj0ip.de/balun-stuff/tuner-baluns/ 

AGAIN, if you think you have to run legal power all the time, you should
look elsewhere for an antenna.  

If you run moderate power and design the matching scheme correctly, it will
work just fine.  It does not have to be a Rich Measures mega-solution -
though his matchbox is indeed a masterpiece!

Running openwire fed antennas is not difficult but it's not exactly
"plug-n-play" either.  You have to understand a little bit about the
impedances you will be confronted with on the various bands.  AND DON'T
EXPECT YOUR TRANSCEIVER'S BUILT IN TUNER TO BE ABLE TO DO THE JOB.
(Exception: Elecraft in some cases).

73 - Rick, DJ0IP
(Nr. Frankfurt, Germany)



-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Rob
Atkinson
Sent: Friday, February 19, 2016 12:28 PM
To: tentec at contesting.com
Subject: Re: [TenTec] 229 and 238 tuners mod

I had one of those 238 matching networks once and sold it.  There are a few
commercially manufactured ham feedline/antenna transmatches out there that
are decent but they are sadly no longer made.  The Unique Wire Tuner wasn't
too bad for 1KW and less (all power here in terms of CCS).  It had a nice
Johnson roller inductor on a ceramic form and a good turns counter and
ceramic shaft insulators.  The Johnson KW Matchbox is acceptable for
balanced line, as is the TMC TAC, but that one is almost impossible to find.
I have not seen anything currently in production that is any good.  They use
cheap parts and the prices
are ridiculous.   There are good reasons for that from a modern
manufacturing and cost/profit standpoint, but that is no reason why a ham
has to be a consumer of these products from the likes of Pal-Star, Ten-Tec,
MFJ and the rest.

If you are going to modify an inferior network you may as well homebrew one
with vastly superior parts from a hamfest, or improve an earlier L network
such as the aforementioned Unique Wire Tuner by simply adding a bigger air
variable cap and Russian RF doorknobs.  I did that and have a great
continuous duty network for 160 m. that should handle up to 500 watts
carrier.  Its inductor is a popular Johnson 22  microhenry  inductor rated
for 5 amps.

L networks can be easily constructed with items such as a Gates 10 amp
roller inductor, and nice wide range brass Cardwell air variables, ceramic
standoff insulators and shaft couplings, all found at hamfests
if you ever venture outside into the flea market.    Brass nuts, bolts
and washers are at most hardware stores.  There was a tuner discussion
recently on the 160 meter email list and it was sad to see so many
recommendations from hams for manufactured networks, instead of designs for
building one.

> Am unable to tune my 135' HB 2" ladder line fed antenna any lower then 5.2
MHz when using a MFJ 259 Analyzer. All frequencies above 5.2 tune fine. The
tuners rotary inductor acts like it needs >more turns to get down to 75m.
Addng a 1000Pf cap t the back of the tuner does not seem to help. Adjustment
of the LO or Hi Z switch does not seem to have any effect. I'm sure I'm
overlooking >something but haven't found out what is is yet.
>

Your problem is you are using a design intended primarily for unbalanced
line or unbalanced loads to attempt impedance match _and_ transform a
balanced line to an unbalanced source.  I know it has a "balun" in it so Ten
Tec could advertize it as a do everything tuner but it is really not
suitable for your use.  Build a link coupled balanced network, there are
designs for them on-line, or if you must, get a pair of inductors and do the
Rich Measures balanced matching network design.  There are really no
substitutes.  It should be trivial to achieve a 50 ohm impedance for your
ham gear with one of these circuits.  Get some parts and experiment with
clip leads.  This is supposed to be one of the fun things to do in this
hobby.  Not something you buy your way around.

73

Rob
K5UJ
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