Resistive SWR Bridge for QRP

My Heathkit SWR meter is not sensitive enough for QRP operation, here's my solution.
I based the design on a schematic published by G3ROO & G4WIF in the "GQRP Club Newsletter." Thanks Ian and Tony.

I like those 270-1803 Radio Shack plastic boxes since they are exactly the same size as a standard 3" square meter (even down to the mounting bolt spacing matching up to the face plate mounting holes.) Only problem is shielding. Heavy Duty Aluminum foil and a little contact cement remedied that. I made sure to leave some over the screw holes to provide contact with the cover.

A hand nibbler took care of shaping the metal face plate to the meter. I found some dry transfer lettering at Goodwill specifically for "Electronic Devices." The sheets already have the words spelled out which made things quicker than using individual letters. I sprayed them with clear enamel to protect.

I made the circuit board to mount directly on the studs of my Honeywell 0-150 uA and shunted it with 300W to make it read 0-1 mA.

Instead of the 51W 2 watt resistors I used two parallel 100W (2 or 3 watt, I'm not sure I pilfered them from a JBL subwoofer amplifier.) This should let me use at least 4-5 watts for a short time.

I decided on BNC connectors for both input and output. The 2-pole 3-position switch is actually a Radio Shack 275-1386 which is a 2-pole, 6-position. I drilled a small hole in the top at the proper place to stop it half way, threaded a small screw and cut the head off flush. Voila! a 3- position switch.

Here we are posing next to my Tuna Tin 2. (Not actually operating cause I didn't have my antenna tuner built yet.) That's the tomorrows project...

Back to Homebrewed Test Equipment for my shack.
Back to QRP Stuff.

Home to Rock Radio