[ARC5] [Milsurplus] Smart People: Attenuators

[J. Forster]

Almost all the power will be dissipated in the input resistor. If you made
that 10 W and used 1/2 W for the others, you should be fine.

BTW, I'd not bet on getting 36 dB is one stage in one shielded box. I's
split it into two attenuators of 18 dB or better a 20 and 18 dB. Only the
input resistor will dissipate significant power.

FWIW,

-John

=================



> Need the help of you smart people again.
> I built a "utility" linear HF amplifier to help put QRP transmitters
> on the air.  Works great with the correct drive,
> which is 10 milliwatts.
> I need to attenuate drive levels from a couple of hundred milliwatts
>  up to about 6-7 watts, so need a variety of pi-type attenuators.
> The resistance values are no problem,
>  because someone wrote a Java app:
>
> http://chemandy.com/calculators/matching-pi-attenuator-calculator.htm
>
> My question:
> What's the formula for the Wattage rating of each resistor?
> For instance:  If I have a 4-watt drive signal and need to get it down
> to 10 milliwatts (assuming 50 Ohms in and out),
> I need to attenuate 36 dB.
> That's shunt in 52 Ohms, series 1580 Ohms, shunt out 52 Ohms.
>
> How to calculate the appropriate wattage of the three resistors?
> Common sense says the shunt input should be big enough to
> sink the entire carrier power, while the series and shunt out
> could be smaller.  What's "right?"
>
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