We are assuming it is the big one?
There were two (2) versions of the matchbox. One was originally
sold as a 250 watt version, later changed to 1 KW because of the
primary use of ssb.
The large version was originally called the "KW-MAtchbox", and that
was for 1 kw/ 100% plate mdulation or 3KW PEP.
If that is the one you have - then you're okay. Otherwise, I have
seen the smaller version with the coil melted down unde a good KW
The large one is about the size of a modern day, 500 watt microwave oven.
Again - that is the one you want - or you'll be stuck with less than max
allowed transmit power. de KL7HF
Jim Reid wrote:
> Aloha again from Kauai,
> Thanks to the many owners of the Matchbox's who responded
> with information.
> In summary:
> Now, what have I bought??
> 1. It has both balanced and unbalance output terminals; is rated
> as fit for 1 kW input transmitters;
> Correct, AM modulated transmitters. Had two responses saying it
> handles both CW and SSB at todays 1.5kW legal limit, no one has
> seen arcing, etc.
> 2. Unit has two variable caps, and
> a tapped inductor; and is said to be link coupled. Does it
> have a band switch?
> Yes, a five position band selector: 80, 40, 20, 15, and 10. The
> switch selects equal tap points down from the secondary coil
> ends. On 80, the entire secondary inductance is used. On
> 10, just a few turns either side of coil center.
> Will it tune 160? No, apparently not enough inductance
> on the secondary, and someone noted that there did not
> appear to be enough room in the case to add turns, nor
> install a bigger coil. Anyone out there been able to modify
> the box to operate 160?
> 3. Why two tuning caps. I suppose because the link itself is
> not adjustable?
> Correct, it is not. But, unlike the balanced tuner circuits
> shown in current editions of the ARRL Antenna Book, there is no
> capacitor in series with the primary transformer coil. Both
> multiple section tuning caps are in parallel across the entire
> secndary coil. C1 is a regular dual section, unit with each
> section connected to one end of the secondary, and the other
> cap side is grounded. These ard gang-tuned, of course, on a single
> shaft. C2 is the "dual-differential" unit, having each
> differential pair connected in parallel with one-half of the
> C1 tuning cap. That is, each differential pair is connected between
> one end of the secondary coil and ground. This Matchbox circuit
> was published in QST, May 1995, in an article about transmatch
> evaluation written by AI1H, Frank Witt. The article was
> suggested to me by Steve, N1SR, and again, thank you Steve!
> The balanced output from the Matchbox is obtained from between
> the differential pair tuning capacitors of C2. Obviously,
> this is a totaly different appearing antenna tuner circuit,
> than any other I have seen before!
> 4. Will it handle 1.5kW output, CW?
> Yes, and SSB also. In fact, one user commented that it would
> tune more output power that I could probably afford to feed it!
> Wonder about RTTY.
> 5. The internal componets are evidently pretty massive as the unit
> evidently weighs around 50 or so pounds; steel case?
> Yes, the unit is housed completely by a steel case, but
> the weight is probably more like 30 pounds. No one actually
> disconnected from their set up and weighed the box! John,
> K1ER sent along the following:
> "To play with the innards you remove the three knobs, take all the sheet
> metal screws out of the big steel box, and the two pieces come apart. two
> sheets with two 90 deg bends. Front, top, bottom lip. Sides, bottom and
> Big ceramic Cardwell switch, wide spacing on the caps. If you arc it,
> you can get in to fix it.
> I don't think there's room to add turns to get to 160 m."
> Well, that is the summary of info so far. InFrank Witt's
> QST piece, he does give some of his test data on both the
> low and high power Matchbox's. The data is presented in
> very much the same way as the antenna tuner review article
> data in the March 1997 article by the ARRL tech staff. They
> credit Frank and his technique of balun testing and his
> "geometric" test boxes. These boxes are described
> in Part 1, April, 1995 QST, "Hoe to Evaluate your Antenna
> Tuner", by Frank Witt.
> Some brief notes about the Matchbox's from Witt's '95
> test report: the low power unit has a bit lower loss
> than the KW box: eg, 11% power loss on 20 meters, while
> the low power box was somewhat less than 10%, this surprised
> Witt. But as he points out that the tuning adjustment
> of the KW unit is "touchy", perhaps this means quite
> high coil Q, and thus higher circulating current at
> resonance tuning, just a guess by me. He also reports
> that the output balance of the Johnson boxes is the best
> of any of the balanced tuners he has tested.
> So, to the many who requested the summary data, enjoy.
> 73, Jim, KH7M
> On the Garden Island of Kauai
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