This MB-II is equiped with the optional balun that is used to match ballanced open wire line.
It is not obvious from the pictures but on closer examination we discover that this device is nothing more than an all band PI-network. The low impedance side is the input. The high impedance side is the output. Hang a balun off the output and you can match to ballanced loads.
It works. The meter is a little quirky. Seems overly sensitive. It suffers from lowered efficiency resulting from the need of a balun to drive ballanced loads.
The lowered efficiency may not be a concern unless the unit is being used at close to maximum power levels. Under those conditions there may be excessive heating, primarily in the balun. Of course lowered efficiency is also at work at low signal levels and may be evidenced by lowered signal level input to the receiver.
Although we speak of lowered efficiency, there is no data defining efficiency. The difference may be inconsequential. Like 95 percent efficient versus 100 percent efficient. I doubt that it is less than 75 percent efficient.
However, because of the efficiency factor, this unit is not worth the high price that it commands. A much better choice would be an original Johnson KW matchbox which is considerably less expensive and does not have issues with efficiency.
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Last updated Sep-2006
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