Subject: Cell Mod for BC8500 XLT
From: Steve Donnell
> Would sincerely appreciate info on cell mod and other mods for BC8500 XLT > scanner.
> > Please Email :billthis 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.
Source QRZ: The Windows Ham Radio CDROM |
