Heatsunk resistor question

Oops. Make that

Well, a 1/2W resistor might be suitable as a 2W dummy load for something on the order of 10mSec, with a duty cycle of less than 25% (obviously), but I am not sure I would push them any harder than that.

The issue is 'just how effective is that heatsinking'. It might extend the effective power by a little, but I don't think it'll make it possible to run them at 4x rated power for something in the order of minutes. Even if they don't burn up, the internal temperature will rise sufficiently to change the resistance such that the dummy load is not what they think.

Just my $0.02 without actually having some to test.

Cheers

PeteS

For any significant heat loading, there will be temperature effects that make the terminator uncalibrated even if it survives. Heatsinking for dummy loads was done in the past by immersing the resistor in an oil bath, consisting of a paint can of mineral oil with a UHF connector soldered to the lid, and with a termination resistor immersed in the oil inside. It was called a 'Cantenna'.

Folk who work with low frequency signals (mine were about 2 Hz) find that op amps and their feedback resistors are both temperature-modulated in the most inconvenient ways, and it is often beneficial to heatsink even low-power resistors. I've also heatsinked op amps.

No problem. Just build the terminations with a 1-dB return loss.

Cheers,

Phil Hobbs

Really, the only way to find out is to do one.

I guess my point is, why "later"? Just do it, and you'll know. As others have said, a metal thing like that can do 2 watts without even noticing, but a 1/2 watt resistor could get awfully hot in the middle.

Good Luck! Rich