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Re: [TenTec] 4229 Tuner Balun Replacement?

To: Rick - NJ0IP / DJ0IP <Rick@DJ0IP.de>
Subject: Re: [TenTec] 4229 Tuner Balun Replacement?
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Reply-to: geraldj@weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sat, 13 Nov 2010 21:09:40 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
On 11/13/2010 8:31 PM, Rick - NJ0IP / DJ0IP wrote:
> Jerry, we all prefer a link coupler tuner.
> Unfortunately there are no commercial units available anymore, at least not
> in the amateur radio market.
> Most of the old Johnson Viking matchboxes on the market are really grubby
> these days, and even if you find a good one, they are very limited in their
> matching range.

True for their tuning range. It never was great and hasn't included WARC 
bands ever.

Maybe I'm an old pack rat and should put a few things up for sale, but 
the last tuner I built (wasn't balanced) I built from parts on hand. My 
big tuner that I built about 1964 uses alligator clips for band 
switching, so I can tap the output coil at any turn of the coil. Its 
kind of overbuilt, that output coil is from a 5 KW broadcast antenna 
match box wound of quarter inch wide flat strap, wound on edge, so the 
alligator clips fit on nicely. And I can connect it for series or 
parallel tuning, for the two output capacitors that are mounted on 
ceramic standoffs and coupled with insulate shaft couplings. There's 
probably enough coil to get down to 500 KHz which is a another problem 
at higher frequencies. Might wish for more capacitance too at 500 KHz.
>
> Sure you "could" build one but unless you are only interested in one or two
> bands, the challenge would be finding an appropriate bandswitch.  These are
> really quite complex.

RF parts has bandswitches. Most often figured for amplifier PAs but if 
two section for a Pi-L tank there would be enough switch for a balanced 
tuner.

> I think you would have to build it yourself, which is beyond the ability of
> most of us.

I've lost track of the number of link couple tuners I've built. My big 
tuner has too much coil for 20 meters and higher, so I have built 
individual tuners for 15, 10, 6, and 2m, maybe even 220 and 432 though 
I've not used the HF center fed wire on 220 or 432. I may have built 
more than one tuner per band. I used split stator capacitors for those 
and coils wound of #12 bare stripped building wire with a gap in the 
middle for a variable link. Places like Dan's Small Parts still has 
small air variables suitable for the higher bands. Its quicker to swap 
tuners than to flip a bandswitch and retune and these tuners are often 
no more than a 4" cube in volume, mostly exposed. In these smaller 
tuners I tuned the whole coil and adjusted the antenna taps for the 
handiest match, and soldered them together.

> Or, as an alternative you could use a Z-match, which requires no bandswitch,
> but they have reduced efficiency at some impedances.  There may still be a
> high power version of the Z-Match available from UK Linears.

Never used a Z match.
>
> The MFJ and Palstar designs for symmetrical matchboxes are not as good as
> the link coupled, but they get the job done in good fashion.  You need some
> pennies for those boxes though, but they'll handle a kilowatt.

The unbalance of a coaxial tuner feeding a balanced load while being 
driven through a balun isn't enough to upset any antenna. There's no 
need for the post balun tuner to be physically balanced in my opinion. 
Sure it looks nice but its not necessary. Then the balun on the matched 
side always sees its rated impedance, without the core or insulation 
smoking wild impedance variations of the tuned antenna and can work 
well. Even handier one or two the the MFJ automatic tuners get their 
power through the coax when set up for remote location. So that power 
can pass through the balun.
>
> For 100w, I have found the MFJ-974B to be a great little box.
> Previously, at field day, my club used an old Viking 275w version, link
> coupled matchbox to match our openwire fed doublet.
> It had great difficulties finding a match across all bands.
> We had to play with feedline lengths.

True, the Johnson Matchbox has a limited tuning range, but its handy 
when it works.
>
> The last two years we replaced it with the 974B and were able to obtain a
> good match on all bands.
> We have retired the Johnson Viking.
>
> Here for high power, I use a home-brew coax balun and a Model 238 tuner.
> Works great on ALL bands.  As with any openwire fed antenna, I sometimes
> have to "adjust" the feedline length when I change the QTH.
>
> In the February or March edition of QST there was a really great article on
> d-i-y 4:1 current baluns.
> I suggest building one of these and placing it external to the matchbox,
> with a very short length of coax between the balun and the matchbox.  Any of
> the solutions proposed in that article will have less loss than any of the
> suggestions previously made in this thread (except for the link coupled
> matchbox, of course).

The balun loss on the antenna side of the tuner can be severe because of 
it being operated at impedances way outside the range it was designed 
for. I got a rude awakening one time at a club station tuned up a tuner, 
couldn't hear signals though, unhooked the antenna and the impedance 
match didn't change. I had tuned to the toroid balun, instead of the 
antenna probably because the balun had a much lower impedance than the 
antenna at that frequency. That has made me unwilling to operate a balun 
at arbitrary impedances.
>
> 73
> Rick (running openwire since 1963)
>
>
I've run open wire, twin lead, and Ma Bell shielded direct burial cable 
on my long center fed wire. Twin lead flopped about too much in the wind 
for the strength of the 20 guage copper conductors, e.g. too good an 
airfoil. 1" space #18 copperweld didn't fly in the wind, but it 
shattered when a slight breeze moved it when covered in a quarter or 
half inch of ice. The bronze strip wrapped direct burial cable did well 
for years, until the antenna took a hit by lighting, then the cable went 
open at numerous spots. I'm figuring on using what RS calls heavy duty 
twinlead on my next centerfed wire, but I plan on punching holes in the 
dielectric every 6" or foot and threading polyester line or parachute 
cord through them making a half turn or a full turn around the line 
between the holes to have a much greater tensile strength. The turn 
around may also upset the airfoil effect. So far this year, moving has 
occupied too much of my time to get that up and now its started to snow 
nearby. I do have a box of 3" ceramic insulators that would make a fine 
balanced line with some #10 or 12 copper weld. I think I have a bit of 
#10 copperweld that hasn't been in the weather that would work good for 
that feed line. I still have my double extended 75 meter zepp that has 
outlived two supports and three feed lines and a new QTH without room 
for the full double extended zepp where I'd wish to put it with the 
center handy to the house, but there is room for a 160 meter dipole 
between the trees with the feed point at the flag pole.

73, Jerry, K0CQ
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