[TenTec] Home brew RF power attenuators

[Dr. Gerald N. Johnson]

On Mon, 2007-12-31 at 22:14 -0600, Bob McGraw - K4TAX wrote:
> Fair Radio Sales for some of them.   Mouser for some and Surplus Sales of 
> Nebraska.  Although the latter is a bit pricey but they do have the parts 
> and values often needed.  They also have some non-inductive values of 
> slightly higher wattage.  I've found these to perform good up to about 30 
> MHz or so.  Probably best to check with a bridge to see if any resonance 
> exists near the intended operating frequency.
> 
> http://www.surplussales.com/Resistors/CarbonComp/Res-CarbonComp_5.htm
> 
> In some cases I use the Pi configuration.  I find easier to mount components 
> thus being two BNC chassis connectors on a small metal plate, a resistor 
> from each center pin to ground and a resistor between the two center pins.
> 
> 73
> Bob, K4TAX
> 
I have found the 3, 5, and 7 watt metal film resistors perform well at
RF and will tolerate a ten times power overload. They may ignite their
surroundings when treated that way but that is not enough to cause the
resistor to change value significantly. Yes they often are cut in a
spiral, but I've been unable to detect inductance greater than that of a
straight rod the size of the resistor body and a half inch of lead has a
lot more inductance. The resistance swamps any inductive effect.

So called "non inductive" wire wound resistors are probably non
inductive through audio frequencies.

Low value (up through a couple hundred ohms) resistors are now made in
TO-220 transistor cases needing heat sinking and some are specifically
made for RF service up to microwave. So they must be essentially
resistive blocks like carbon composition (except IRC) resistors were.

Mouser still showed a few 2 watt carbon composition values the last I
looked.

73, Jerry, K0CQ