Well, I have been keeping the SMR guy happy testing, probing, and monitoring his system. He gave me an EFJ 8625 full-duplex mobile and 8180 full-duplex portable.
The 8180 actually looks like a flip phone, pretty radical. I think the manufacturing difficulty is not too different from the Motorola Visar, which is even thinner, such that the battery is twice as thick as the radio. Here in the Viking CX 8180, they’ve added a duplexer I assume. The shop doesn’t have the service manual for it, and the speaker is none too loud and the transmit power is only 1 Watt, so to them it’s not so good for general use. For me who loves to play with radio, it’s great and it looks like I have quite an old flip phone.
The 8625 has 12 Watts of transmit power, unlike any of the 3 Watt bag phones. Three watts are lost in the duplexer, which prohibits talkaround in this and other full-duplex models. Instead of say 10-15 mile range of a bag phone, you get 50+ mile range from the tower with SMR interconnect.
So the way 800 MHz full duplex interconnect works is so:
- incoming caller calls common number (unless you have a DID controller), then enters your repeater-group number (5 digit)
- outbound you select closest repeater, enter number and press send. half-duplex get dial tone or busy.
In some ways it’s rather impractical in the rapidly converging digital cell phone age, but I feel like I have the ultimate in pre-cellular communications with the EF Johnson 8180 and 8625.