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Old August 18th 09, 05:30 PM posted to rec.radio.shortwave,rec.radio.amateur.equipment
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Default Can I use wirewound resistors to build an HF attenuator?

In rec.radio.amateur.equipment dave wrote:
Ralph Mowery wrote:
"dave" wrote in message
m...
I need to lose about 5 dB from a 15 Watt exciter. Thanks.


Simple answer is no.

While you can build one with wirewound resistors , the normal formulars will
not usually work at RF and you will have a lot of inductance to deal with.
Even the socalled non-inductive resistors are only so at the audio
frequencies.



Can the inductive reactance be cancelled with capacitors? I'm mainly
concerned with 40, 30 and 20 meters.


It becomes too frequency dependant to bother with.

Use a T attenuator.

See:

http://chemandy.com/calculators/t-at...calculator.htm

You will likely have to use series or parallel combinations of resistors
to get the values required anyway.

You can also play with using two attnuator sectoions to see if it makes
the resistor values (and wattage required) simpler.


--
Jim Pennino

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