[Elecraft] Re: QRP Dummy Load

[Tom Hammond]

Hi Don:

I'm afraid going to 1% or 0.5% resistors is gonna crank up the cost.

But I understand your concern. I'd go for anything with <1.1:1 VSWR.

73,

Tom

At 01:24 PM 8/6/03, Don Wilhelm wrote:
>Tom and Ron,
>
>My two cents - a known accurate dummy load is important to me.  Most of the
>time 20% off is OK because I am just using it as a loading device.
>
>HOWEVER, when I want to make measurements, it must be accurate, and I really
>want it to be 50 ohms rather than 51 ohms. (Don Brown take note please).
>The math to calculate power, etc. is much simpler when the resistance is 50
>ohms, and IS the stated design point for most equipment.
>
>73,
>Don W3FPR
>----- Original Message -----
>|
>| >One question I don't see answered here is, "How accurate do we need a
>dummy
>| >load to be?" It's a different world not that out rigs are "pre-tuned" and
>| >expect a certain non-reactive impedance at the antenna terminal.
>| >
>| >Since so many people use commercial dummy loads without a problem, I'd
>guess
>| >the current crop of dummy loads is just fine. They seem to be accurate to
>| >within only about 20% or so! They claim an SWR of only 1.3:1 or so.
>| >
>| >Is that adequate?
>|
>| A question I've been considering as well.
>|
>| Since many builders will be using their dummyload for both SWR and Power
>| calibrations, I'd think we'd like to have RF resistance accuracy as good
>as
>| possible, GIVEN reasonable pricing. And, we'd certainly want to reduce
>| residual reactance as much as possible.
>|