Sunday 1 June 2014

TF3LJ Power and SWR meter

Last year I built the TF3LJ Power meter and subsequently gathered the parts to build his Power and SWR meter.  It was time to finish the project.
The first consideration was the directional coupler. I remembered I had built one for the ill fated W7IEV project so this was unpacked. The basic unit is rated at 100W and has -40dB coupling for both forward and reverse signals. I found the fixed 20dB BNC attenuators bought for the W7IEV project so that would give -60dB for both forward and reverse signals.
I also found the two AD8307 detector boards from the W7IEV project so all I needed was to mount the Teensy 2++ arduino style module on a carrier board and was ready to go.
I mounted the modules and an LCD in a 8"x6" x 3"  Box. Probably would have gone in a smaller one but it was available. The software was installed from Lofturs Site and all worked smoothly.
The software does have the ability to produce an alarm signal when a preset SWR is exceeded. This could be used to Inhibit an amplifier. It is the phono connector on the back panel below.
Front Panel View (KX3 into two 50 ohm dummy loads)
Inside view. Teensy is on the left then 2 detector modules

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