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[VHFcontesting] Ham IV rotor readout fix - FYI

To: NEWSVHF@mailman.qth.net, vhfcontesting@contesting.com
Subject: [VHFcontesting] Ham IV rotor readout fix - FYI
From: George Sintchak/WA2VNV <wa2vnv@optonline.net>
Date: Mon, 19 Nov 2007 00:04:25 -0500
List-post: <mailto:vhfcontesting@contesting.com>
 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
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