Questions About Charleston SC TRS

[zerg901]

I have several questions about the Charleston SC Motorola TRs after reading the Phase II Report on the fire at the Sofa Store.

The report is available here - 3rd item down in the middle of the page -

http://www.charlestoncity.info/dept/content.aspx?nid=1375

<http://www.charlestoncity.info/dept/content.aspx?nid=1375>


1. At 2227 of the transcript, apparently a portable radio transmitted over a mobile radio. How is that possible?

2. At 2326 and at 2451 there were messages from unknown users. How can there be unknown users?

3. How could there be messages heard at the scene that were not heard on the tape? (this was mentioned in a footnote)

There is extensive radio information in this report.

I also have a generic question about TRS that use a control channel. When a mobile or portable trunked radio is transmitting, that radio is not able to receive traffic from the control channel at that time - correct? If an Incident Commander was transmitting a 30 second message, and someone activated their emergency button, it might take up to 30 seconds for the IC to become aware that an emergency button had been activated. Correct? (Unless he/she had a 2nd radio nearby). Everyone at the scene except the IC might know that a button had been pushed. (I am assuming that once the IC released the PTT, an alert would sound and indicate that a emergency button had been pushed.)

I used the search function here at radioreference.com but I did not find any other discussions of this Charleston report.

Peter Sz

 

[RKG]

With respect to your "generic question," this subject is a bit complicated. You might want to get your hands on the SmartNet II system controller manual and study the sections on trunking format options. In particular, how the system responds to a "barge in" depends on whether the system operator has elected "Message Trunking," "PTT Trunking" or "PTT-ID" trunking. And note that, while the initiator and any other radio shifted to an OSW-assigned voice channel does not have access to the control channel for the duration of the grant, they do have access to the sub-audible data sent over the voice channel for the same duration. This, for instance, is how priority scan works on a SmartNet system.

 

[slicerwizard]

1. At 2227 of the transcript, apparently a portable radio transmitted over a mobile radio. How is that possible?

Apparently, their equipment is programmed for message trunking, which makes it all too easy to do that. Even if the system and the radios were properly (IMO) programmed for transmission trunking, Motorola site controllers will occasionally send channel grants to two radios on the same talkgroup at the same time, with the same result - lots of hetrodyning and nobody gets through.

2. At 2326 and at 2451 there were messages from unknown users. How can there be unknown users?

Because they are using message trunking. When the radios walk over each other they don't TX their radio ID on the control channel first. I wonder why they didn't go with PTT-ID - that way you at least have ID's to go with the hetrodyning.

3. How could there be messages heard at the scene that were not heard on the tape? (this was mentioned in a footnote)

This seems improbable, but who knows - Motorola's products are not bug-free.

I also have a generic question about TRS that use a control channel. When a mobile or portable trunked radio is transmitting, that radio is not able to receive traffic from the control channel at that time - correct?

Correct, although you wouldn't know it from the "my dispatcher relative told me so - they can send a message to a radio while it's transmitting and poof, it's gone" nonsense that shows up here from time to time.

If an Incident Commander was transmitting a 30 second message, and someone activated their emergency button, it might take up to 30 seconds for the IC to become aware that an emergency button had been activated. Correct? (Unless he/she had a 2nd radio nearby). Everyone at the scene except the IC might know that a button had been pushed.

Correct.

(I am assuming that once the IC released the PTT, an alert would sound and indicate that a emergency button had been pushed.)

That's what I would expect. No radio ID would be displayed though as the IC's radio would've missed that information.


That report is a disturbing read. Some of the practices of that department are anything but professional. I guess it was only a matter of time before their sub-par procedures intersected with a highly dangerous incident and led to the inevitable result.

I also have to wonder why the one channel pair that is known to pick up skip across a body of water isn't protected (e.g. used last / when all other channels are in use)