If I'm not mistaken, what you have are wire-wound power
resistors and are NOT suitable for RF dummy loads because
of excessive reactance. The dry dummy loads commonly used
for RF dummy loads use carborundum or some similar
material to eliminate reactance.
On the other hand, if you are still wondering what effect
the small variance from an ideal 50 ohm dummy would
have, forget about it. Most dummy loads I have checked
never are exactly 50 ohms, and have extremely low SWR
whether they are 49 or 52 ohms or whatever. The main
thing to have is a pure resistance.
Metal film resistors can be used for fairly low reactive loads
or use a bunch of carbon film or carbon composition small
wattage resistors to build up the required power handling
capacity for your transmitter. Just realize that carbon
resistors tend to become permanently altered in their
resistance values is subjected to overheating. They also
age poorly over time.
Get a commercial dummy load if you are needing more than
a dummy load of a few watts that could be made up from
standard resistor values. It isn't worth the time and trouble to
try and build a high wattage load when economical ones
can be purchased. The various ham catalogs have a pretty
wide selection to choose from in whatever style appeals to
you.
The 15 watt Radio Shack dummy load is easily obtained
and will withstand any QRP power level you subject it to, plus
it will handle brief application of 100 watts with no change in
value. I have heated mine very hot for short periods of time
and it always returned to 50 ohms. If you need more wattage
than 100w, MFJ and others have a good selection of dry
type dummy loads.
73,
Gary Surrency AB7MY
S&S TAC-1(40&80m) and ARK30, AT-11 (QRO and QRP)
QRP-L #571 Chandler, AZ (near Phoenix)Grid Square DM43BH
Az ScQRPions
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