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.
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