What else could be seen inside was something that looked a milled cavity with a tuning screw with some sort of a piece of polymer material on it that possibly was a part of the tuning structure. The dark grey neck between the bottom side of the coupled line and a pad was measured as a 50 Ohm resistor, and the pad is apparently a microwave decoupling capacitor. Here is a close up of the directional coupler structure. The directional coupler circuit had a 50 Ohm terminating resistor on one side of the coupled line and the other side of the coupled line connected to the ceramic transmisison line and exited the box through the third SMA connector marked "Power Monitor". The signal path looked as follows: from the RF Input SMA connector on the top right the signal goes into the first circulator, exits on the left side of the circulator and into the second circulator, exiting on the left side of it and going into the third circulator, exiting from the top side, and through the direcional coupler exists through the RF Output SMA connector on the top left. Not only it was fascinating to see something that was stamped with actual day when the board was manufactured, but also it was interesting to see that such microwave technology existed in early 70-s. The board was stamped with the Raytheon logo and date of "14 Jan 72". On the microwave board I could immediately identify three microwave circulators, a few filters and a directional coupler. There were two snap-on small heatsinks glued to the box, and the board was held in them with the IC and transistor bodies snaped into the heatsinks. The power supply board had a IC and a transistor and the way the board was mounted was interesting. The third board had something that appeared to be a simple transmission line on a white ceramic substrate. It had a FR4 board which was supposedly a voltage regulator and another board with a microwave circuit on a black glossy substrate. Anyways, I bought the box and went home where I opened it and what was inside looked pretty interesting. The guy looked puzzled and said he never paid attention and would not know. That was something unusual and I asked the dealer if he knows why so high voltage to power the circuit. Something that looked weird to me was what looked to be the power peg was marked "+90V". And it was a pretty nice milled heavy gage aluminum box with cover and RF connectors. I grabbed a heavy looking aluminum box with SMA connectors and power pins, with a "Solid State Amplifier" marking on the cover, which the dealer was selling as a "nice RF box for projects" or something. Some time back browsing tables at a hamfest I came across a dealer who was selling RF items. Who knew that bying a junk RF box was going to turn into a fantastic learning experience.
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