Questions have often come up about what criteria is used to coordinate repeaters. The Alabama Repeater Council has developed and refined over the years, a set of guidelines for 2-Meter, 6-Meter, 220 MHz, and 440 MHZ repeater coordination requests. The required separations for each band are described below:
On 2-Meters, the required separations are as follows: 100 miles for co-channel and 5-kHz, 90 miles for 10-kHz, 50 miles for 15-kHz, and no spacing is required for 20-kHz or more. In the 144.5 to 145.5 band, all channels are 20-kHz. In the 146 – 148 band, coordination is based on either 15-kHz, or 20-Khz channels as the situation dictates. The 15kHz channels start at 146.010 and recurs every 15-kHz, i.e., 146.10, 146.025, 146.040, 146.055, etc. The 20-kHz plan starts as 146.020 and recurs every 20-kHz, i.e., 146.020, 146.040, 146.060, and so on. If you now have a repeater that is on the 20-kHz plan and you think it might work better on the 15-kHz plan, or vise-versa, contact the Frequency Coordinator and he will check it out for you.
Per a 2003 A.R.C. vote, the spacing requirement for 440 MHz and higher has been changed from 100 miles for co-channel to 75 miles. Since the channel spacing on UHF is consistent 25-kHz, no other guidelines are necessary. When considering 440 MHz repeater coordination, please consider 100 mile pairs before choosing the 75 mile criteria. Also, 100 miles is the basic criteria for 6-Meter and 220 MHz
Other factors are also considered. In the case of mountain-top or tall tower repeaters, more than 100 miles may be required to alleviate interference. Occasionally two very local repeaters can exist with less than 100 miles spacing. These and other possible factors are left up to the discretion of the Frequency Coordinator. A detailed computer study of the terrain between two sites is often conducted to aid in the coordination decisions. Unless it is obvious that no interference will occur, we usually require approval from any short-spaced co-channel repeater operators.
It should now be obvious that it is very important for the Repeater Council to have an accurate location for your repeater. There are a few cases where the coordinates provided for a repeater were off by 20 to 30 miles. Unless there is reason to believe otherwise, the Council accepts the parameters provided by the trustee as correct.
(Dave Baughn, KX4I – Previous ARC President, previous ARC Freq. Coordinator)