[Boatanchors] Radio Transmitter testing

[SBJohnston@aol.com]

Bill -

You want a "dummy load" for transmitter testing.  It is basically a resistor of the same value as the transmission line the transmitter was designed to feed, and of sufficient power rating to dissipate the expected power output of the transmitter.  It should be in a shielded enclosure to prevent the signal from being heard by others.

One old trick is to connect a regular household AC light bulb as the dummy load resistor on the output of the transmitter.  It works pretty well for older tube-type gear that is forgiving of output matching, but is not a perfect match for any transmission line and so may strain solid-state equipment.  It has the added advantage of being visible to the eye - you can see how bright it gets.  If a 60w light bulb gets to the same brilliance on your transmitter as it would plugged into the 120 house current, you must be getting about 60 watts output from the transmitter.

A big disadvantage of the light bulb is that is it not shielded and so some of the radio signal is radiated as if it were an antenna (well, it is to some extent).  You could put it in a shielded box, I suppose...but then you couldn't see it.  -grin-

Steve  WD8DAS

sbjohnston@aol.com