Fire Department: VHF <-> 700/800 P25 Repeater

[spitzman]

Hello everyone,

I am looking for someone with experience or advice on building/configuring a VHF <-> 700/800 P25 repeater system. My fire department is in a tough position with failing radios and Starcom P25 nearly completed but still 8+ months out. We are currently using a mixture of MACOM radios and Kenwood TK-790H's. Our new P25 radios are Motorola APX 8500's.

I am looking for a repeater that can take our VHF freq and repeat that on a P25 700/800 freq and vice versa for full bridging between our legacy VHF and new P25 Starcom. An alternative would be taking the new Motorola audio out/ mic inputs and somehow connecting that to a controller that would interface also with our older radios. Somewhat like a DIY repeater.

Any input into a solution would be very much appreciated!

 

[Cameron314]

Not a DIY thing. Trying to do that between analog and digital like that will sound horrible.

 

[mmckenna]

Yeah, not a good idea.

If your existing VHF repeater is failing, a better approach would be to purchase a replacement VHF repeater. Good Quantars are easy to find for a few hundred bucks. Get it tuned up by a qualified tech and use that until the trunked system comes along.

Running a cross band/cross mode repeater like that has the potential to sound like crap. Plus, the Starcom guys probably will not appreciate it. Cross banding between conventional and trunked systems also often comes with a lot of delay challenges that make for unhappy users.

 

[ramal121]

Quite a few departments around here marry their legacy analog channel with a new whiz bang digital system. Doesn't sound bad at all. The only thing weird thing is the analog side, you have the robotic digital voice along with all the static we know and love with analog.

Of course this is done through a patch at the dispatch console. Is this possible for you?

 

[prcguy]

The city of Big Bear Lake, CA fire dept seems to have a VHF link tied to a county 800 system. Maybe you could contact their radio people and have a conversation to see how they did it?

 

[gesucks]

You can not legally connect you VHF to STARCOM with out their express written permission.

THE ONLY PEOPLE YOU NEED TO TALK TO ABOUT THIS MATTER IS STARCOM

 

[kayn1n32008]

Not a DIY thing. Trying to do that between analog and digital like that will sound horrible.

It depends. I've used analogue<->P25 and the audio wasn't particularly terrible. I've also used DMR<->P25, also not particularly horrible.

The biggest issue with trying to analogue to P25 trunking with 2 mobiles, is the problem with the channel grant request delay between keying the P25 radio amd the infrastructure granting a voice channel and sending the subscriber to it.

The proper way to do this, is going to have the VHF repeater properly patched to the P25 talkgroup at an infrastructure level, likely through a console patch, not using 2 mobiles back to back.

You need to be having this conversation with your dispatch centre's techs/trunk system operator not on a hobbiest site.

 

[emacs]

As others have said the first step would be speaking with the P25 sysadmins. Best to get permission, or see if they can offer a solution like a console patch, before spending time and money on a solution only to have your radio stunned!

That said, there are solutions that are a bit more elegant than taking pumping the RX audio and COR from one radio into the TX audio and PTT of another, and vice versa. Midian, for instance, makes the IS-2, which will do impedance matching of the audio, and has a buffer to account for the delay before a PTT request is granted on the trunked system.

 

[kayn1n32008]

Midian, for instance, makes the IS-2, which will do impedance matching of the audio, and has a buffer to account for the delay before a PTT request is granted on the trunked system.

Not an ideal solution for public safety. If the trunk radio is not granted a voice channel, what ever you are transmitting won't go over the trunked talkgroup. It's not a solution that should be used.

 

[W6RAM]

As others have stated check in with your system's admin. You might want to consider something similar to a JPS interop gateway with two donor radios connected, that would fix your P25 delay you would have with a simple cable.

 

[kayn1n32008]

As others have stated check in with your system's admin. You might want to consider something similar to a JPS interop gateway with two donor radios connected, that would fix your P25 delay you would have with a simple cable.

And if the trunk system doesn't grant a voice channel it still won't fix the issue of the VHF analogue comms not going over the trunk system.

Anything the involves using using a trunk system subscriber in a cross band/cross system configuration has a much better than 0 percent possibility of failing to access the trunking system.

the OP appears to be needing a long-ish term solution to have the analogue repeater tied to a trunk system talk group.

The ONLY proper way to do this, is to have the conventional repeater interfaced directly to the trunk system, as a resource controlled by the consol