Elementary radio system question?

[oklameatman]

Our local FD communicates via VHF-HI repeater. Obviously there are mobile and hand-held radios in use. Like most, I monitor the repeater freq. rather than the input freq.. However, sometimes when the personnel are on scene, doing their thing, I hear only one side of the conversation on the repeater freq. This is especially true when the firefighters are in a building (on a hand held radio) talking to the batallion chief who is usually outside. Simple logic says that the firefighter's radio in the building is able to get its signal to the repeater - thus the reason I can't hear. But how do the other personnel hear the hand-held - assuming their radios are designed to receive the repeater frequency transmission? Are some radios designed to receive both the repeater freq. AND the input freq?

 

[oklameatman]

Simple logic says that the firefighter's radio in the building is able to get its signal to the repeater

Actually, thats supposed to say that the firefighter's radio in the building is UNABLE to get its signal to the repeater. Sorry.

 

[jgarber311]

Many agencies- fire depts mostly will switch to another channel when on the "fireground".
With all the fancy bells and whistles of trunked radio and some repeaters more times than not, they cannot talk outside of a burning building.
For these mission critical comms the department will switch to a tactical channel which ends up being the input frequency of the repeater but with no CTCSS tone or the receive frequency of the repeater with a tone. That way they can talk to the truck engineer or scene command via the most reliable means of communication- simplex.
They use the same channels as the repeater pair simply so they don't have to get a license for another channel which can be expensive.
Hope this helps!
Jamie- KB8TTR

 

[oklameatman]

But I'm still hearing one side of the conversation via the repeater. Perhaps this will help explain:

Repeater = 154.16
Input = 153.77

When crew is in building, I hear one side (bat chief) of 154.16. Therefore he must be receiving 153.77 (the only mobile freq licensed) on his radio? If they all switched to a 'non-CTCSS' mode of transmitting, why does the repeater still receive and transmit? Thanks!

 

[nmfire10]

This is what is happening:

The people in the building are on direct (aka- talkaround). This means they are transmitting and receiving on the repeater output. Anyone within range of the portable will hear it including command outside. Command however is still on the repeater channel and is using that to talk to the firefighters inside rather than direct. This prevents him from having to change channels everytime he needs something from dispatch.

With the firefighters inside on direct, they don't have to worry about not reaching the repeater and being unable to communicate with anyone. Everyone outside can hear them fine because they are close enough.

 

[oklameatman]

Thank you. I was wrong also. . .the FCC DB shows 75 transmitters with the repeater freq. Makes perfect sense.