[Amps] Drake W4 Wattmeter Question

[Lloyd Korb]

I have a question on my Drake W4 wattmeter.  Since I don't have a high power
wattmeter I picked up the W4 on eBay to use on my AL-1200.  I have found
that the calibration is off starting on 15 meters.  I did some comparisons,
at the 100 watt level on my TS-2000, with my Bird with a 100A element and my
Drake WV4 VHF wattmeter. I didn't go below 15 meters as the WV4 is only good
down to 20 MHz. The Bird 100A is good from 25 - 60 MHz. This is what I
found:

 

Freq            Drake W4       Bird 43       Drake WV4

50 MHz          70W            100W            95W

28 MHz          75W              95W            90W

21 MHz          80W              91W            90W

14 MHz          85W

  7 MHz          90W

 

I took a look at the W4 schematic and couldn't find anything, obvious, that
would make the meter so frequency sensitive.  Any ideas would be
appreciated.

 

73,  Lloyd   K8DIO