Hey Fred,
I've given up on watt meters, even Bird.
My old Cantenna even "Moves" in value and is
currently at 54.2 ohms. You need to measure
your load with a DMM.
Then I use a Tektronics somethin' or other
and get a Peak to Peak, or just Peak voltage
across whatever value my Cantenna is at and
"Do the Math".
Don't use one of the scope probes that
came with the scope. I use a chunk of RG-58
with a RCA jack on one end and a BNC on the
other end. Jump out, (or remove) that "R"/Diode
thing Heath put in there.
Now you can get a Peak to Peak, or just Peak
"Voltage" across your load. Adjust your scope
for as "Full" of a screen you can get. Record
your voltage then I use this:
http://www.random-science-tools.com/electronics/dBm-Watts-volts.htm Plug in your values and your all set.
If you really want an accurate meter, Calibrate
at your frequency of interest and don't trust it
at any other Freq.
Here, I have Tektronics 465, 475, 2215 and
a couple 2465's. Even have a Hitachi device
someone gave me. You can check the scope easy
enough with a battery and a DMM. You can check
your DMM with a resistor.
About as close as "WE" can get in the basement!
GL es 73
/Dan