Trio PF-810

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Switch for two antenna outputs, calibration knob for accurate SWR measurement. Radiant power display subtracts reflected power from forward power giving good indication of antenna matching.
The manual claims that this is a "laboratory quality, professional instrument".

When I took it apart I found the four diodes (two each in series) indside the dircectional coupler assembly were all shorted. My guess is "Harry the Ham" had put two much power through it and then of course it was "U/S". I searched on the internet for any manuals and found the user manual on BAMA.

The circuit diagram is in this manual but there are very few component values and there is just a function diagram of the directional couple, not the actual circuit with details of the parts used. The directional coupler is in a diecast box with F connectors for the input and output. The lid (bottom) is glued and I used a Dremel tool with a cuting disk to remove the epoxy so I could get inside.
If anyone out there can help with more details or even a service manual I will be very pleased.
I presume the diodes are germainium types and the fact that two are used in series in each case strengthens this possibility. The breakdown voltage of typical Germamnium diodes is less than 80 volts as a rule. I will replace them when I find my collection of suitable diodes and see it it works. Perhaps other damage was done !

The manual claims that this is a "laboratory quality, professional instrument". It would be nice to be able to verify that some day.


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Written by and Copyright, Phil. Storr © Last updated 10th Spetember 2013