Examining the Johnson Matchbox ATU

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N3DRB The Derb:
a german company called Anneke licensed the rights from EFJ and made their own version for a short time. it had a series condenser in line with the link coil where the EFJ version just grounds the far end. I have my KW version open right now to change the meter over to a expanded scale RF ammeter instead of the swr bridge which never worked. Put the SWR meter back the way it came in the slant front box. Works great.

I dont see how the small and large versions could be so different as to actually hear a signal difference on rx between the two. So many other factors would matter more that would cover up the difference  - like natural QRN on the low bands, rx noise figure and other internal rx noise on the high bands.

I vote balderdash on that claim.  since loss should be reciprocal on tx or rx, the difference, if any, should b easy to measure. But it sounds whacked to me.

We agree on the misconception that the KW version receives better than the 275W version, Derb. Kurt Sterba had a lot of good stuff in his 'Aerials' column in World Radio, but he sure was off in left field on that one. Incidentally, I edited the first published edition of Aerials for WR.

In addition to my having a 275W version of the Matchbox I built a tuner using BC-610 plug-in inductors. Consequently, I used the link-coupling method, which also provided the balun function. However, I did use a series cap in the link circuit, which canceled out the reactance in the link circuit. Without that cancellation it was impossible to reach a perfect 50 +j0 match.

I give you my best wishes for a speedy recovery from your new problem, Derb--should never have happened!


The Aerials books are at home, so I'll try read and paste Kurt's comments in this forum tonight, just to be certain that I am not speaking out of school.

Kurt's comment made an impression on me at the time, enough so I recall that I lashed up both units in a A/B test a few years back, didn't seem to discern any difference on my end, but I had not real instruments other than my ears. My little 275 watt unit fits under the shelf on my operating desk, and is about the same height at the 75A1, so I just use it.

I did press the KW unit into 160 meter duty last year, sits on the top shelf, with an outboard air variable clip leaded across the right tuning cap. Think it was based off Bowie Bill's ER article, only Bill used doorknob caps.
Sure it is not too efficient, at full strap the big indictor gets somewhat warm on old buzzard transmissions.


N3DRB The Derb:
thank you Walt :D There is a new wrinkle on that on which I will make another post about.

This thread also reminds me of the problem with Lew McCoy's design that he called the "Ultimate" transmatch. As with the designer(s) of the Johnson Matchbox, McCoy
also didn't understand the use of the dual-section capacitor he placed in the otherwise standard T network. Murch and other mfgrs adopted the McCoy version, also not knowing that the second section of the Ultimate performed no useful function. The same as with the designer of the Johnson Matchbox, McCoy believed the dual-capacitor provided a voltage divider, and thus an impedance divider--WRONG!

In the 1970s I analyzed the McCoy Ultimate(?) version, only to discover the second section of the capacitor provided no useful function--is unnecessary and superfluous. I was then a consultant to Denny Had, the owner of Dentron. I told him about the uselessness of the second section, and he was delighted to learn that, because he was just about to order a new batch of the more-expensive dual capacitors for their tuners.

Shortly thereafter I visited the ARRL Lab, where I demonstrated with the Dentron Supertuner that the second section of the cap achieved no useful purpose. Doug Demaw and Laird Campbell witnessed the demonstration, and later DeMaw published the results in QST.

From then on Murch and other tuner mfgrs began using a single section input cap instead of the dual, thus reverting to the standard T network configuration.


PS--I posted this somewhat earlier today, but apparently it got lost somewhere.


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