Muxlow said:
How do you find out what the band plans are for new systems?
It's just algebra.
F = Base + (LCN - offset) * step
F is the channel's frequency. LCN is the channel number. Offset is the lowest channel number for a range of channels. Step is the channel spacing. Increasing the channel number by 1 increases the frequency by this amount. Base is the frequency the lowest channel in for that range.
You need at least two confirmed channels. Start with the control channel. Determine it's frequency and channel number. For Motorola systems use 380 as the offset (for starters). Confirm a second channel's frequency and LCN #.
For two channels - the difference in frequency should be the difference in LCN #'s times the step size.
Hypothetical example:
LCN 480 @ 408.5 Mhz
LCN 580 @ 411.0 Mhz
Channels 480 and 580 are 100 steps (or channel #s') apart and 2.5 Mhz apart.
2.5 Mhz / 100 steps = 25 khz
Our step size should be 25 khz. If you get a odd number like 6.666 khz - you may have a multi-table system. The two channels would be mapped to different tables.
You'll want to use an offset that is lower than the lowest numbered channel. 380 is the lowest for Motorola systems on VHF and UHF. 759 is the highest.
You
could use 480 as the offset and 408.5 as the base. To use 380 as the offset, reduce the base frequency a proportionate amount. Reducing the base frequency by 100 steps or 100 * 25 khz. So 408.5 minus 2.5 Mhz gives use 406.0 Mhz for an offset of 380.
After you've deduced a band plan, compute the other channels and verify them for traffic.
