[VHFcontesting] Ham IV rotor readout fix - FYI

George Sintchak/WA2VNV wa2vnv at optonline.net
Mon Nov 19 00:04:25 EST 2007

 I decided to see what I could do to fix my Ham IV rotor noisy readout until I could change out the rotor and rebuild/replace the readout pot inside the rotor. Delivery of the part from Hy Gain is 2+ weeks (minimum) so that probably means I'll get it in mid January. 

I tried this simple fix. I used a 12 Volt bulb (automobile lamp, ~1/2 Amp) in series with 12 Volts connected to the 300 Ohm readout pot as follows. Jumpered both ends of the readout pot together (rotor wire #3 & #7) and connected thru the bulb to +12 Volts, negative 12 Volts to the pot wiper common #1 ground terminal. The bulb will limit the current to ~1/2 Amp so I don't burn out the pot. Then run the rotor from end to end limits twice. Bulb only lights up as the wiper gets to either end of rotation, the bulb limits the current. Less current flows (minimun ~80 mA when North) during the rest of the rotation due to the pot's parallel combination resistance. Anyway, I did it end to end twice, then reconnected all back to normal and, bingo - it cleaned up the problem. Now my readout is smooth and continuous - like new !!! I guess a small amount of dirt or corrosion had built up after ~20 years of use and the normal readout circuit current is too small to burn/clean away dirt on the pot/wiper. 

The end result is I don't have to remove/rebuild the rotor and of course, now I'll have spare parts (insurance) that I won't need now. More stuff to put on the shelf and never find it again. Time will tell how well this fix will last, hopefully until sometime after the January contest.

George, WA2VNV
50 thru 1296

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