SCM stands for Station Class Mark. The SCM is a 4 bit number which holds three different pieces of information. Your cellular telephone transmits this information (and more) to the cell tower. Bit 1 of the SCM tells the cell tower whether your cellphone uses the older 666 channel cellular system, or the newer 832 channel cellular system. The expansion to 832 channels occured in 1988. Bit 2 tells the cellular system whether your cellular telephone is a mobile unit or a voice activated cellular telephone. Bit's 3 and 4 tell the cell tower what power your cellular telephone should be transmitting on.

Bit 1:
0 == 666 channels
1 == 832 channels

Bit 2:
0 == Mobile cellular telephone
1 == Voice activated cellular telephone

Bit 3/4:
00 == 3.0 watts (Mobiles)
01 == 1.2 watts (Transportables)
10 == .06 watts (Portables)
11 == Reserved for future use

E-07. What is a SIDH?

SIDH stands for System Identification for Home System. The SIDH in your cellular telephone tells the cellular system what system your cellular service originates from. This is used in roaming (making cellular calls when in an area not served by your cellular provider).

Every geographical region has two SIDH codes, one for the wireline carrier and one for the nonwireline carrier. These are the two companies that are legally allowed to provide cellular telephone service in that region. The wireline carrier is usually your local telephone company, while the nonwireline carrier will be another company. The SIDH for the wireline carrier is always an even number, while the SIDH for the nonwireline carrier is always an odd number. The wireline carrier is also known as the Side-B carrier and the non-wireline carrier is also known as the Side-A carrier.

SIDH is often abbreviated to SID.

E-08. What are the forward/reverse channels?

Forward channels are the frequencies the cell towers use to talk to your cellular telephone. Reverse channels are the frequencies your cellular telephone uses to talk to the cell towers.

The forward channel is 45 mhz above the reverse channel. For example, if the reverse channel is at 824 mhz, the forward channel would be at 869 mhz.