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Old August 17th 08, 11:09 PM posted to rec.radio.amateur.antenna
Richard Clark Richard Clark is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 2,951
Default Size of dummy load required to tune 160 Watts CW, 200 W PEP SSB ?

On Sun, 17 Aug 2008 16:36:42 -0500, wrote:

My old TS-520S is said to put out 160 watts DC CW and
200 watts PEP SSB .


Hi Dave,

DC? (Yes, I know, straight from the specification sheet, but
nonetheless: DC?)

Whats the minimum dummy load requirement to tune it ?


Add 50% for safety factor. Or simply ask yourself, do you need to
tune up with full power? Kenwood is usually engineered well enough
not to demand this.

There are kits for 100 watt dummy loads. Would that be
enough for brief ( ~ 10 sec ) tuning ?


Sure. Better question to ask is "can I trust the claims of this kit?"

Are there standards as to how the rating of a dummy load
is to be interpreted ?


Something short of:
1. throwing the solder of the connections (a temperature under the
eutectic point if 61/39 tin/lead).
2. ignition;
3. personal harm.

The dummy load's rating can be extended through cooling by forced air
or immersion - so its environment is as much a part of the
specification as anything (it doesn't work as well inside a stove as
it does a refrigerator).

If you are building your own (implied by your reference to a kit);
then it behooves you to maintain the lowest heat path resistance
between the load (the resistor) and the coolant. This generally means
a very tight gas-free bond between the load (the resistor) and the
heat sink and the absence of insulating air on the heat sink surface
(either in the form of an air pocket, poor circulation, or a bubble).

Last of all, how sure are you that the load is actually the Ohmic
value you need? The harder you push it, the less likely it will be
that value. In that case, derating to 25% to 50% is called for.
Frequency can be an issue too.

Caddock's MP9100 50 Ohm resistors are a useful jumping off point for
building your own load.

73's
Richard Clark, KB7QHC