PFR-3 SWR Bridge and balanced line tuner

This was an interesting section to build. I found one 470 ohm resister to be missing. Turned out that the BOM listed one, which I had already installed, so could not figure out why I could not find it. Careful checking of the instructions revealed that there are actually two 470 ohm resisters in the kit, so I had to go scrounging through my junk box to locate a spare that I could use. The alternative was to ask Doug Hendricks to send me one (that would delay the build progress by at least 2 weeks) or travel to my nearest electronics supply store to purchase one. Luckily I located one in an old kit that was no longer used.

Everything in place and ready for the power output measurement and adjustment.

Once that stage was complete, it was time for the final testing. I hooked up a 7ah battery that was putting out 12.06v, then connected up a dummy load, an MFJ-860 SWR Wattmeter and a straight key. On key down, I saw around 2W on the wattmeter. This got me thinking.

How accurate is the wattmeter? I decided to get a handle on this before fiddling with the windings of L8, L10 or L12. So I hooked up my trusty DC40A (another Doug Hendricks kit) to the dummy load and my bigger MFJ-941E versa tuner. You see, I know this rig puts out 1W with 13.08v, so this would be a good reference point. Sure enough, I got 1W on the dial.

So now it was the turn of the PFR-3 with the MFJ-941E but with 12.06v. I was now more confident at fiddling with the coils to get a 5W reading. My rig was reading well over 5W now, so I played with the spacings of the coils until I received 5W output on all bands.

After adjusting the windings of L8, L10 and L12 I got a steady 5W out on all three bands.

Next is to mount everything into the enclosure.


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