Monday, April 16, 2012

Busy with Arduino and RF Vector Impedance Meter Projects....

FINALLY got all the little Arduino boxes built, and moved on to the RF Vector Power Meter I've been building for a year ( ! ) or so. This is the one that I went on a rant about winding the toroids for sometime back. WELL....I finished the toroids, and that meant I could finish the coupler. Last night I mounted the main board in the enclosure, and tonight I'm going to make some preliminary measurements in preparation for calibrating it.
I had to order some Schottky diodes to build an accurate RF voltage probe with. I have dummy loads that are almost exactly 50 Ohms from 1MHz to beyond 1GHz, so I have my "Known Impedance" to work with. Once I build the RF probe, I'll be able to accurately measure the voltage across the load, and calculate the power developed by my Elecraft K2, which will allow me to calibrate the "Power" part of the meter. I also have some 50 Ohm delay lines of known length, so I'll be able to calibrate the "Vector" part of the meter.
Knowing the forward and reflected power, the meter will calculate VSWR, and by knowing the phase angle between the voltage and current on both the forward and reflected ports, it can calculate the complex impedance of the antenna system, or anything else that gets connected to it.
And after I've cleaned up this project, I'll get back to finishing up the Collins 75S-1 receiver I've had torn apart for almost TWO years. I never meant for this one to take so long. I got it for about $75, and it was filthy, and didn't work quite right. I replaced all of the defective tubes, recapped it, and replaced some out-of-tolerance resistors. It was working much better, but before I did the alignment, I decided to "clean" it, and before I knew it, I had it torn down to almost the bare chassis. I replaced all the ceramic insert RCA jacks on the back panel (some had broken inserts; all were rusty), which meant drilling out the rivets, unsoldering/resoldering a whole bunch of connections, and then touching up the solk screened designations on the rear panel where I bumped them with my Dremel tool while I was grinding a dimple into the rivet head so I could drill out the rivets.
This one definitely got out of hand, but it should be really nice when I'm finished. The paint was in excellent condition under all the grunge, the knobs buffed out beautifully and I repainted the indicator lines and put new spun inserts in them. I even took Scotch-Brite and Nev-R-Dull to all the crystal cans for the heterodyne, BFO, and calibrator crystals.
Back to the workbench!

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