[Elecraft] Measuring power with a scope...

[Don Wilhelm]

John,
My comment on the real 50 ohm load had to do more with the accuracy of your
SWR indicating device(s) and their common lack of accurate readings at low
power levels - when the meter is showing zero reflected power, that only
says that the diodes do not see enough voltage to conduct and the actual
power may  be small but not really zero.  While this may be fine for plain
old SWR measurements at reasonable power levels, it is usually not
sufficient for calibration purposes, nor for the microwatter folks either.

The answer to your second question is no!!!  AC signals including RF follow
the principles of Ohm's law just the same as DC - so for any given fixed
resistance, if you increase the voltage across the resistance, the current
through that resistor must increase too.  The only reason that things look
more complicated with AC signals is because Power is usually computed using
RMS values so the results can be expressed in the 'heating' value for the
power.  Instantaneous Power (non-RMS values) calculations work too if one is
interested in the power over only a small portion of a cycle, but we
amateurs are not usually interested in such stuff.  The current and voltage
relationship is controlled by the load impedance and not by the transmitter.

73,
Don W3FPR

----- Original Message -----
> ...
> As you can probably tell, truly understanding antennas is something I'm
> still working towards.  Hmmm... if the K2 tells me that is is seeing 0.0
> reverse voltage, then even though that indicates a 1:1 SWR I might not
have
> a 50 ohm load?
>
> Here is another question... do all HF transmitters transmit at the same
> current level, just changing voltage (signal amplitude) to change power?
>
>  - jgc
>
> John Clifford KD7KGX
>
> Heathkit HW-9 WARC/HFT-9/HM-9
> Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2/KPA100
> Ten-Tec Omni VI/Opt1
>
> email: kd7kgx@arrl.net
>
>
>
>