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TUCoPS :: Radio :: bc200am.txt

Mod for putting a Bearcat 220 into AM mode




Modification for Putting BC-220XLT In AM Reception Mode

I have come up with a crude mod for the BC200xlt scanner to allow AM
reception in the 136 to 174 range. Why would I want AM in this range you
ask? well I attend several Air shows during the year and the Thunderbirds
use 140 mhz area fregs. As we all know the Uniden switches to FM in this
range, causeing very distorted reception (slope detection). Somebody else
may have already thought of this idea (you?) but here goes. Break the AIR
Trace between dual diode D31 and IC1 pin 8. Connect the center of a single
pole - double throw mini switch to the trace leading back to IC1 pin 8.
Connect one of the other poles to the trace leading back to D31. This is the
"Normal" mode(This just restores what you have cut). Now connect the other
pole to the VHI (VHF HI) line at a easy to locate point. This is the "AM"
mode. What will happen now is when AM is selected the VHF and VHF air band
will all be in the AM mode. UHF and others are not affected. When in the
normal mode everything is just like it always was. I have done this mode
over a year ago so it's still a cloudy in my memory. But it works like this:
The microprocessor sends a high to Q7 to select the AIR mode, by routing the
VHI signal around D31 by means of the switch the AM detector is reselected.
Normaly D31 blocks out the VHI signal allowing FM in the VHF HI range. I
hope my explaination of this mod is clear. It does take some delicate
surgery to do. I also hope I haven't duplicated anyone elses idea.

Thanks


From: BILLY WIGGINS
 


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