...Since I was getting such a good signal from the Diamond, I thought that using the switch would cancel one unit totally while the other was in use. Apparently this is not always the case . I have decided to buy a cheap external antenna for the scanner and place it high on the tower. After all, most of my use will be on the transceiver anyway.
That might actually be worse than using a switch, because when you transmit
the scanner antenna is still connected. Depending on the distance between them,
the scanner antenna can pick up a lot of RF from the transmitting antenna.
Whether or not that is enough to damage the scanner depends on the design of
That may or may not be the case depending on the mounting location of the scanner antenna. If you mount the scanner antenna more or less directly below the transceiver antenna with 8 to 10 feet between them, the scanner should be OK. Just turn it off when using the transceiver.