[Elecraft] Dummy loads for dummies

[Don Wilhelm]

Wes,

What you say is true, and how much it matters in practice will vary 
depending on just how much inductance is present  in those wirewound 
resistors. how much it matters depends of frequency.  The higher the 
frequency, the more it matters - and that is independent of power.

The load in question is for initial testing of a KX1 at 40 and 20 
meters.  If only an indication of some power output capability is 
required, then that load may be sufficient, but in this case, the owner 
wants to know if his KX1 is operating up to specifications, and a 
non-inductive dummy load is required for that purpose, in addition a 
means of accurately measuring the power output at a 3 to 4 watt level is 
also an essential tool.  An RF probe applied across the dummy load may 
provide that indication at 4 watts or less (along with a little math), 
but if the power is much greater than that, it will zap the most 
commonly used diode in the RF Probe (a 1N34).

So you are correct, if simply providing a load to a transmitter, the 
wirewound resistors may be OK, but if they are being used as a 
measurement tool, the results will be incorrect if only the DC 
resistance is considered.  The real result of any measurements done with 
reactive components can only be had by also considering the complex 
impedance of the load.  Measurements with an RF Probe and a DVM will not 
reveal that complex impedance that must be entered into the equation.

73,
Don W3FPR

On 12/27/2016 5:31 PM, Wes Stewart wrote:
> Paul,
>
> You've got a lot of hand wringing comments about how those are probably
> wire wound resistors.  They probably are but in practice it might not
> matter.  It all depends on what exactly you are trying to accomplish.