[Elecraft] Power measurement with a 'scope

[Ron D' Eau Claire]

> Your example states 5W and 50ohm. So, a measured 14.25 is 10% low
> [(15.8-14.25)/15.8]. Going to 10% high, we have 17.40v. These
> yield power readings of 4.06 (19% low) and 6.06 (21% high).
>
> So, your idea was correct but the example had some problems.
>
>
> As to the Cantenna resistance at HF, how do I measure that
> without an accurate power meter? I figured it wouldn't have any
> reactive components at all and the DC ohmmeter would do.
>
> Dan / WG4S +- 3 letters / K2 #2456 +- 0

Egad! Dan. I caught that error before sending it and then forgot to correct
it!

Okay. NO more arithmetic!

The resistor in the Cantenna is supposed to be "non inductive" (i.e.
non-reactive for this purpose). I have not run careful measurements on the
Cantenna, but I would suggest that you are in very good shape if you use the
d-c resistance value. That issue came up on here a year or so ago and, as I
recall, several ops did use the d-c value and it agreed very well with other
measurement methods. Many of the Cantenna's are a good 10 ohms low. After
all, they were designed as a dummy load with a low SWR, not as a "precision"
load.


Ron AC7AC
K2 # 1289