Subject: Cell Mod for BC8500 XLT

From: Steve Donnell 

Bill Inabnett wrote:
> 
> Would sincerely appreciate info on cell mod and other mods for BC8500 XLT
> scanner.
> 
>                         Please Email :  bill@unicomp.net


Hi, the BC-8500 is fairly easy to modify for Cellular. We first wrote 
this up two years ago in National Scanning. Basically, what you want to 
do, is to swap the logic control lines that drive transistors Q4 and Q5 
on the receiver PC board. This can be done with a DPDT switch. 
Transistor Q4 controls activation of the 800 MHz band signal input 
filter. Q5 activates the 350 - 500 MHz band signal filter. By doing this 
logic line swap around, when you set the '8500 to search between 371.19 
and 396.80 MHz, you are actually receiving signals from the 869.04 to 
894.97 MHz(Cellular). This occurs because the radio uses the same range 
of Local Oscillator freqs to receive the 870 Mhz(blocked freqs) area as 
is used for 370 MHz reception(freqs the radioo can be programmed for).

In the case of the BC8500, you also need to do an additional control 
line swap, to that of the control lines that drive transistors Q41 and 
Q42. These set the operating mode of the radio. In the 370 MHz range, 
the default(and only) operating mode the radio can be set for is AM. For 
Cellular reception you need to have Narrow FM mode activated. This is 
done by swapping the logic line that drives Q42(AM mode) to alternately 
activate Q41(for NFM mode).Again, this can easily be done with a DPDT 
switch. This additional feature can also be used to permit AM/NFM mode 
switching for other types of reception as well. In most other 
scanners,like the BC9000, operating mode can be user controlled from the 
keypad.

One further step is the be sure and set your tuning/search frequency 
step rate to 5 KHz for acurate on-channel tuning.   

Before starting this modification, I highly recomend obtaining a copy of 
the BC8500 service manual to serve as a guide. If you'd rather not 
attempt this work yourself, try contacting Cellular Security Group at 
508-281-8892 .

There are a couple of other things you can do with the BC8500 that we 
documented in the former RCMA Journal. These mods include: improved 
preamp ICs, better Tape Out audio, and adding heat sinks to the voltage 
regs.(one on the far right and another near the front of the main PCB) 
Have fun.