Well, I wasn't sure where to post this, but I figured Gear was as good a place as any.
Recently, a lot of people have begun moving away from 2 watt FRS / GMRS radios and using 5-6 watt UHF Radios tuned to the FRS / GMRS frequency range.
ONE, THIS IS ZERO, WAIT ONE, OVER!
NOTICE : If you disagree with using 5 or 6 watt transmitters on the FRS or GMRS bands, or want to challenge the legalities, or are deathly afraid that the police will drop out of the ethosphere and bust you for using overpowered radios, please STOP READING HERE. I'm well aware of the legalities, and frankly that is outside of this discussion.
That being said, below you'll find an article I published on the WP boards describing all the frequency mappings for FRS / GMRS radios and the associated CTCSS settings for compatibility with non UHF players using standard FRS / GMRS subchannels. Note that some of the information in the article was compiled from the public domain. As such, I do not take responsilbity for the accuracy of any information provided, excepting that I can personally attest to the accuracy of the GMRS radio frequencies provided. Furthermore, I do not present this article as an original work, as it has been stated that several portions were compiled from the public domain.
ONE, THIS IS ZERO, SEND, OVER!
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Below is the frequency table for Motorola's talkabout series of FRS and GMRS radios, as they relate to programmable frequencies for UHF radios. I though that given the increasing use of high-end radios, this might be useful:
Motorola Talkabout Cannels
Ch Service Frequency
1 GMRS/FRS 462.5625
2 GMRS/FRS 462.5875
3 GMRS/FRS 462.6125
4 GMRS/FRS 462.6375
5 GMRS/FRS 462.6625
6 GMRS/FRS 462.6875
7 GMRS/FRS 462.7125
8 FRS 467.5625
9 FRS 467.5875
10 FRS 467.6125
11 FRS 467.6375
12 FRS 467.6625
13 FRS 467.6875
14 FRS 467.7125
15 GMRS 462.5500
16 A GMRS 462.5750
17 GMRS 462.6000
18 B GMRS 462.6250
19 GMRS 462.6500
20 C GMRS 462.6750
21 GMRS 462.7000
22 GMRS 462.7250
About "Sub Channels"
CTCSS (Continuous Tone Controlled Squelch System) is an advanced sub-coding system that allows segmentation of a main channel. When you transmit using CTCSS you are transmitting on one of the main FRS or GMRS channels but you are transmitting an inaudible tone that controls the squelch. To understand how this works think of squelch as a gate that opens only under certain conditions. When it is opened your radio allows the signal to be received and you hear the transmission. Normally, squelch is a gate that is activated by signal strength - the signal must be strong enough or the gate (squelch) won't open. In CTCSS squelch is controlled by an inaudible sub-tone - without the proper sub tone the gate (squelch) won't open regardless of signal strength.
An FRS or GMRS radio equipped with CTCSS allows it's squelch to be broken (allows an incoming signal to be heard) only when it receives a special low frequency tone transmitted by another FRS on the same subchannel. To use CTCSS sub-channels you would set two FRS radio's, equipped with CTCSS, to the same channel and same sub-channel. This way both radios would be transmitting the same low frequency tone when transmitting and looking for the same low frequency tone when receiving.
CTCSS is a useful feature when you only want to hear from a certain radio or group of radios and not everyone else since your radio's squelch will only open when it receives the sub-frequency assigned to the sub-channel you are on. This will stop you from hearing other transmissions on the same channel and/or same channel with different sub-channel.
It is important to note that CTCSS does not provide you with privacy - all it does is eliminate the number of signals your radio will allow you to hear! Your transmission can be received/overheard by any other FRS radios on the same channel - Once your signal is on the air, the signal is fair game to be received by other FRS radios, GMRS radios or scanners. Additionaly, any UHF radio tuned to the "parent" frequency, and not subscribing to the CTCSS, will overhear any transmission sent on that channel. The UHF set's transmissions will be ignored by the recieving FRS or GMRS radio however, unless the corresponding CTCSS code is activated on the UHF set.
Amateur radios operating in the GMRS or FRS frequency range can be configured to use CTCSS "Sub Channels" by configuring the CTCSS tone frequency.
The following is a list of sub-channel CTCSS frequencies:
Code Freq (Hz)
1 67.0
2 71.9
3 74.4
4 77.0
5 79.7
6 82.5
7 85.4
8 88.5
9 91.5
10 94.8
11 97.4
12 100.0
13 103.5
14 107.2
15 110.9
16 114.8
17 118.8
18 123.0
19 127.3
20 131.8
21 136.5
22 141.3
23 146.2
24 151.4
25 156.7
26 162.2
27 167.9
28 173.8
29 179.9
30 186.2
31 192.8
32 203.5
33 210.7
34 218.1
35 225.7
36 233.6
37 241.8
38 250.3
Putting it all together
So, if you are using a UHF radio configured to access the 462-468Mhz band for FRS / GMRS access, and you've been directed to use FRS channel 14-21, you would set your transeiver to 467.7125 with CTCSS tone 136.5.
Hope this helps.