At 12:36 PM 8/16/2006, Red wrote:
>Hi, Jim;
>
>If your are working HF, a few 2 watt carbon comp resistors in parallel
>will work Put them in a can if shielding is required, but derate the
>dissipation somewhat and consider heat sinking them. I made one by
>soldering resistors between the center conductor of some RG-8 and two
>pigtails of the braid. It gives low SWR even at 2 meter frequency. I
>didn't shield it and I never apply power for an extended time.
I had contemplated such a thing, but I was looking for something that I
didn't have to build. There's a difference between 30 seconds to screw a
load onto a connector and 20 minutes of getting out the soldering iron,
trimming resistor leads, finding the heat shrink, etc.
And, FWIW, it's getting harder to find carbon comp resistors...Mouser only
has 51 ohm resistors in 1/2 watt
You can get nice TO-220 style packaged non-inductive resistors from Caddock
http://www.caddock.com/Online_catalog/Mrktg_Lit/MP9000_Series.pdf
the MP930-50-1% is about $2.90 each in Qty 10 from mouser
But, they'll need a heatsink of some sort. You could probably use some
sort of clip on finned dohickey for TO220 devices.
So, by the time you buy a connector for a couple bucks, a resistor for $3,
a heatsink for a buck, mounting hardware, and then fabricate everything, a
$10-20 load that's already assembled and reasonably rugged is starting to
look like a good deal.
That said, I have contemplated designing a high power load (for oil
immersion) based on a bunch of the higher power Caddock parts. It would
be a PC board that you'd solder a bunch of series/parallel resistors into,
and then immerse in the traditional paint can of oil. The noninductive
Carborundum/Cesewid/Globar style resistors have gotten pretty expensive in
small quantities.
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