Delay/echo during multi-select on EDACS & VHF

[kyparamedic]

Our dispatch center dispatches everyone simultaneously on calls that involve multi-agencies. Well they used to at least. All of us are on an analog EDACS system except for fire which is on conventional VHF. Now they dispatch fire/EMS simultaneously and law enforcement separately. There was some issue where when they were dispatching on 3 channels simultaneously, about 15s into it we'd lose voice and it sounded like we were hearing the control channel for the duration of the dispatch. Everything still came through on the VHF channel though. So the radio techs told them that to solve the problem, they couldn't dispatch on two trunked channels simultaneously. But they could continue to do it between trunked and conventional channels. No idea why.

So now we're still being dispatched simultaneously with fire, but there is a delay in the audio on either the VHF or EDACS so it makes a terrible echo when you are hearing them both. At one of the stations that is shared between fire and EMS, you can hardly understand anything because of this. Why would this start happening all of a sudden? I know they have done some upgrades to the EDACS system and have added a 3rd site, but it's not being used by everyone right now, one of the law enforcement agencies is testing it prior to everyone being added. Talkgroups used to be patched together in dispatch for the two sites but now operate seamlessly. ProScan will also be enabled once the 3rd site is put completely online. So what did they do that caused this problem?

Thanks.

[HarrisRF]

If they added a simuccast site that has greater distance/time to your control point, then delay would have to be added to ensure all transmissions are simultaneous. Is the VHF heard first, then the EDACS? Without system specific documentation, there could be many reasons for this.

[kyparamedic]

It's a multi-cast system with 3 sites, although most everyone is still only using 2 as they test out the 3rd one. It used to be that the two sites were setup as 2 separate systems. The common talkgroups on each site were patched together in dispatch. Basically, dispatch had to do a multi-select to talk on the same channel on both sites. Now it works as a single system although we still have to manually switch between the two sites until they reprogram all the radios to use all 3 sites and enable ProScan.

[morganAL]

Most sites are connected back to the central switch (IMC) by T-1 either through the phone company or microwave. The conversion from analog to digital and back to analog at the far end will inherently create some delay. Normally this isn't an issue since the user is typically only listening to a trunking radio and a millisecond or two delay isn't noticed.

[kyparamedic]

The thing is, it's worked fine for years. Now all of a sudden we're getting this echo. I'm not personally involved with the radio setup so my technical information on it is 3rd hand. If the FD would just get onboard and switch over we wouldn't have this headache.

[kyparamedic]

We have 3 sites up and running now and still have the delay on the one. If one radio is on this site and another radio is on a different one, there's a very noticeable delay. They say it's a timing issue and they're "working on it." Have been for 3 months.