[Johnson] Small Johnson Matchbox has its limits

[Richard Peterson]

I used a small Johnson Matchbox myself, but be warned. These are great units 
and beautifully built, especially for feeding balanced feedlines if you want 
a balanced feedline. That said, the M-Box cannot and will not handle as 
great (or even nearly as great) an imedance excursion as today's more 
commonplace T-network tuner (or in my view, even an L-network).

Remember, the Johnson M-Box came from an era that typically required "tuned 
feeders" and hams had to have feedines of specific lengths, else, they would 
not be able present a reasonable antenna/feedline combination that their 
trusty M-Box could handle. In other words, if you are like a lot of guys 
nowadays (including myself), you will find that an unmodified M-Box will not 
be able to tune any old antenna/feedline that you present to it.

I modified my M-Box Junior (without drilling any holes!) by raising the 
input coil above ground and inserting a series variable capacitior of about 
250 pf, and that helped a little -- but it was still a temperamental thing. 
And even though I was running less than 200 watts SSB, it was easy to get 
the caps to arc-over because the thing was not tuning properly.

Summary: I got rid of it and built up my own high-pass T-network tuner (like 
you can purchase).  And it works much better than the M-Box. You see, there 
is a reason that they quit making the M-Box type of design...today's designs 
are more versatile. Again, however, the M-Box is superior for feeding a 
balanced line -- if that is important to you. Hope this helps.

- Richard, WB5NEN

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