[Heathkit] impedence of dummy loads

[k5jv]

Greetings to all.

        The HeathKit Cantenna has a normal, published,  resistance of 50
ohms.  But, just like everything else, it has a tolerance, a +/- factor.
The resistance of the element will vary with heat.  If you get them too hot,
the resistance will permanently change, usually an increase in resistance.
Frankly, I prefer one that has a cold reading of slightly less than 50 ohms.
That way, when it heats up with normal use, the resistance will be more
approximately 50 ohms.  If the element reads open, there are two probable
causes;  the strap holding the element is either loose or broken, or the
element itself is bad (not very likely with a GloBar).

        Several years ago I modified a Cantenna for high power use by
circulating water through a pipe immersed in the oil.  It worked great.  I
ran the output of an 8877 into it for long periods without damaging the
element.  A standard Cantenna is not designed for high power applications.

        Actually there is no need to have a dummy load be exactly 50 ohms
unless you have some impedance-critical application.  This may present a
problem with solid stade finals and amps.  It presents absolutely no problem
with older transmitters with tunable finals.  If you take a look at the
specs of some of the older gear you will notice that the design impedance
differ, usually higher, that 50 ohms.  Do not toss out an, otherwise good,
dummy just because its resistance measures a little high.

73 de Lon W. Cottingham, K5JV

1110 Golden Bear Ln.
Kingwood, TX 77339
281-358-4207
281-433-7532 Cell