InterceptRadio.com Forums

While visiting the South Center Mall, Seattle area, I was picking up police and fire calls in the 820 range. This is not in records but I saw one of these calls unfold only two blocks away. From North County these signals are too weak to receive. It seems to be a small set of only about 3 frequencies.

You were hearing the inputs. When a user keys up the mic, it sends a request to the controller. If the talkgroup is not in use, the controller assigns a pair of frequencies to the talkgroup. One will be a frequency that all users will listen on, and the second is a frequency that the user will transmit on. The latter is know as the input frequency, and this is what you were hearing. In the 800MHz band, the offset (difference) is always 45MHz.

Hope that made sense, I'm posting mobile and probably have a typo or two in there.