Converting VHF or UHF repeaters from analog to digital may not be quite as simple as you may think. It turns out that digital repeaters often do not talk as far as analog if you simply replace an analog repeater with a digital repeater. The reason being that digital receivers like to see a near perfect impedance match and the lowest possible noise level. Analog receivers have similar requirements, but are a little more tolerant.
There are four IMPORTANT considerations that must be addressed when you change from an analog to a narrow band digital repeater. We are going to tell you about ONE of the four things you need to know at this time. We'll tell you about the other three later.
You can make digital repeaters work BETTER than analog by starting with your duplexer. If it is over ten years old - REPLACE IT. This also applies to antennas and transmission line systems. Now, let's like at the not so obvious things, beginning with the cables that connect the repeater to the duplexer. If they are over ten years old, REPLACE THEM!
Measure your old cables. If they are not cut to the proper length, they can cause you some real problems. Start by measuring the cables between the repeater and the duplexer (they will generally be around 2 feet long, sometimes black, sometimes a metallic copper color). To determine the proper length for LMR400 .405" black cable or LMR200 .195" cable go to www.info4u.us/Cable_Calculator.xls. Other cable calculations are available on request.
Normally, the transmit frequency will be the cable marked TX on the back of the radio and LO on the duplexer. The cable for the receiver will normally be marked RX on the repeater and HI on the duplexer. If in doubt, always use the TX and RX markings on the repeater to be sure you are measuring the correct cable.
