RE: [Amps] Power metering in linears

[craxd <craxd1@ezwv.com>]

Tom,

Stripline type RF sensors are narrow-banded and generally won't work 
with that type of band spread. The toroidal transformer should work if 
the core is rated for the complete frequency range like 3-30 MHz. If 
not, you may have to add a switch to kick in another potentiometer just 
for 80 meters and maybe 160 meters. To get the meter to null is another 
thing and has to be done to read forward and reflected power. You may 
just try different toroids first before doing any modifications.

Will Matney


Hello technicians,

I was adding a power meter to a new homemade linear. I used the directional coupler of the "Digital PEP Wattmeter and SWR calculator" from an old ARRL handbook (1987). I did not get a too deep null on calibrating, so the directivity was only 20 dB. As I only wanted to monitor the output of a linear with that coupler, the directivity was sufficient. 

The problem: The output voltage for a given power is the same from 40-10m, but nearly null on 80m and different on 160m.

Then I tried the design from the linears in the W6SAI handbook. They use Amidon 50-6 toroids. The output voltage ón 160 is about 1/2 of the voltage on 10m. 

Has anyone successfully built a directional coupler with constant frequency behaviour from 160-10m?

I would like to have proven designs.

Thanks!

Tom, DJ5RE


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