Just about every Motorola 800 MHz radio is designed to transmit in the 806-825
MHz range and transmit and receive in the 851-870 MHz range.
There are several issues you need to overcome:
1. The software can be over-ridden by hex-editing the MAXTRAC.MDF file.
2. Those radios have good front end filters that only pass 850-870 MHz. You
could remove or short them out and then the receiver might hear something
around 806-825 MHz.
3. These radios operate by mixing the input signal with a second signal. This
produces a sum and difference signal. The radio only accepts the difference
signal, which is about 45 MHz. The VCO in the radio, which determines the
operating frequency, normally operates about 45 MHz below the frequency you
want to hear. Due to the mixing process, you can also get it to receive
something if you get the VCO to operate about 45 MHz above the frequency you
want it to hear. The front-end filters prevent the radio from normally hearing
the other signal. To get it to receive 813 MHz, it has to operate at 858 MHz.
To fool it into doing that, you'd need to program it to receive a frequency 45
MHz above that, or 903 MHz. Then the software will tell you it's out of range,
so you're back to step 1.
You might have better luck with an 800 MHz SpectraTAC receiver, as they're
designed and built to receive 806-825 MHz. You just have to find one, order a
channel element on the frequency you want to hear, tune the receiver, and
you're good to go. Unfortunately, they're not programmable, and channel
elements cost about $50 to recrystal, so you better be darn sure about the
frequency you want to pick up.
Bob M.
==
--- On Mon, 12/8/08, Mike Dietrich [EMAIL PROTECTED] wrote:
From: Mike Dietrich [EMAIL PROTECTED]
Subject: [Repeater-Builder] Re:800 MHZ RECEIVER
To: Repeater-Builder@yahoogroups.com
Date: Monday, December 8, 2008, 6:55 PM
Hello to the group,
I am trying to make a maxtrac or gtx 800 radio receive down on 813 mhz which it
normally doesn't reveive on.
All of the software says it's out of range and won't accept it.
Any ideas whether it will work and/or how to do it?
Thanks in advance,
Mike
