[TenTec] Johnson Antenna Tuners article in Electric Radio, March 2001.

[John Unger]

A couple of months ago I modeled and built a double extended Zepp for 40 CW. It is about 193 feet long and is fed with 17 feet of 450 ohm ladder line. I connected the coax feed line through a 1:1 balun at the bottom of the ladder line. The antenna is about 40 feet high.

Eznec 3.0 shows the impedance at the 1:1 balun feed point to be about 43 ohms resistance and a few J impedance. It's a 1.2:1 to 1.3:1 match for my rig at 7050 mHz; absolutely no need for a tuner there! The antenna has a fairly narrow band width, and I need the tuner for 40 SSB. I think the 2:1 SWR bandwidth is about 150 kHz. The Zepp loads easily on all higher frequency bands with my TenTec 238 tuner (had to get the TecTec plug in for this newsgroup somewhere...).

The performance of this antenna on 40 has been spectacular; I got lots of glowing reports in the Virginia QSO Party and felt very LOUD. It's not oriented well for working Europe, but that will be a changed soon when I put up another one.

BTW, Eznec shows that this antenna also has a ~ 1.3:1 ohm impedance when fed with 6" ladder line of a similar length.

As always YMMV...

73 - John, W4AU


At 10:28 4/5/01 -0400, you wrote:

>Several months ago, I was contacted by several people on this board who were interested in learning more about the E.F. Johnson Antenna tuners.  Please be advised that the March, 2001 (latest issue) of Electric Radio Magazine has a very interesting article describing both the 250 watt and kilowatt models. This is the only source I have ever seen that has actual side by side photographs of both units showing their rather massive internal components along with schematic diagrams of each.  The article also explains how to modify them to operate on 160 meters.  The author is using them to center-feed a 180 foot long hertz (dipole) antenna for use on his favorite bands of 160, 80 and 40 meters.  I have not verified his math, but the author states that on 40 meters, a 180 foot long dipole will act a double extended zepp and has 3 db gain and can be used as a dx antenna. This seems reasonable. (Note: the terminal impedance will not be anywhere near 50 ohms; probably closer to 1000 !
>ohms and will have a large unknown reactive component so a tuner or matching stub is needed.)  The author is using common 450 ohm low loss ladder line to connect from the tuner to antenna.  The author's comments about using the Johnson tuners exactly duplicate my experience; except I used home made, unknown impedance - 5" spaced, open wire line with excellent results.  The tuners really work great for what they were designed to do, provide tremendous bandwidth ( 80 -10 meters operation) with very high efficiency using balanced feed to a dipole, hertz or any balanced type antenna.  They were not really intended to be used with coaxial cable, but can be modified to work with coax.  (I really discourage modifying them or the use of coax in this manner.)  I think the author said he is operating with about 300 to 500 watts of 100% plate modulated a.m. (his favorite mode) through them with no evidence of arcing or heating of the components.  I do not remember his name or call but !
>this info. is in the article.  For anyone wanting to understand exactl
>excellent book entitled  Reflections, Transmission Lines and Antennas  by Mr. Walter Maxwell or his series of six articles entitled "Another Look at Reflections" published in QST in the mid 1970's. - 73's- Corn - k4own.


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