EDACS link to P25 Trunked!

[Roadwolf]

I am faced with a little challenge. The need to link 2 different trunked systems together at my shack for inter county operation. I will be using an Orion and I believe a supplied XPR2500.

Now, sure, we could cut trough red tape and configure a 4 wire patch link between the systems, but with money and politics and other bull****, us radio guys decided it was easiest to just hook up 2 mobiles and be done with it. The police want this done and it is a safety issue - but it is more of a favor the neighboring county is doing for our police department, as they have better coverage in an area behind a geographic feature than we do, where a small area of our police departments coverage is needed.

But I know that will be annoying, when once one system keys up and opens it's talk group, you now have to wait for the other system to do the same. So it would be a bit of a training thing to tell the cops, hey - wait a couple seconds before you talk on this talk-group.

But I wonder if there was a way to speed that up? Anyone ever attempted this?

 

[BMDaug]

So… “cutting through the red tape” seems to imply circumventing the system admins of the respective systems… that’s a bad idea… That said, this is essentially how most vehicular repeaters work… the link between the radio and repeater is just analog audio and some logic that triggers PTT.

If you attempt this, it is absolutely imperative that you set a relatively short CCT… otherwise, you have a very real possibility of locking up that TG until someone physically intervenes… that’s really REALLY bad when lives depend on that communication.

I think this is a bad idea and I would recommend instead that you set this up as a console patch that can be stopped at any time by any dispatcher. It doesn’t have to be a line patch… it could be as simple as trading radios with the other department and properly interfacing that with the console. At the very least, make sure that the radios can be inhibited by dispatch if (when?) things go wrong.

-B

P.S. Did I mention that this is a bad idea?

 

[Roadwolf]

Bad idea I agree. I am the closest thing they have to a system admin for my side. I am also co-ordinating with the system admin for the other system and this is what we both came up with as a solution to the no money to spend issue. The talk group on either end will be specific for the patching process - so other communications wont be interrupted if things go bad, aside from a frequency being used up until the ghetto built repeater patch gets a swift kick.

The red tape is a funding / money issue. No one wants to pay for hardline or internet or microwave links or the installation of antennas higher up on the tower at either site. But like I said, both police agencies want this to happen in some way.

My hope is that this works well enough, but inspires some funding for them to want to clean it up and make it better and find some money for a more proper solution.

 

[BMDaug]

You’ll need the accessory port pinout for both radios. I could do this with two XG100Ms with two 44 pin connectors and a spare piece of ethernet cable, but I’ve never done anything aside from talk on an XPR2500!

You’ll need ground, COR, PTT, TX anudio, and RX audio… you’ll probably need an audio level matching circuit and maybe some transformers for isolation purposes. If the systems are both in the same band, you’ll need some serious distance between the antennas. As much as you can get… I’d say you could use filters to stop desense but when you’re trunking, and without any coordination between the systems, you can’t predict a specific voice channel and you can’t guarantee that the receive and transmit frequencies will be of sufficient spacing to use filters at all! Best case scenario would be if the EDACS system is vhf and the P25 system is 7/800.



-B

 

[jeepsandradios]

You would have more success adding one of the radios to a console at either county and doing a console patch. That way if there is an issue it can
be stopped. The other issue you need to remember is desence. If both systems are 800 make sure the antenna's are far enough apart. I can see this for a temp patch but i would not rely on it for officer safety for long term.

 

[Roadwolf]

The console option is ideal, but again, due to locations it would require a mast mounted antenna at either site which currently no one wants to pay for. Luckily the systems are on different bands entirely UHF/800, so desense shouldn't be an issue. Tho spacing antennas is always ideal in any case. I plan on also using yagi's.

Am not certain what radio exactly is going to be supplied from the other county. I had thought he said an XPR2500. but I know he did say he would have the proper accessory cable for it for PTT and such. I've been living in the Harris / Kenwood world for so long, been a while since I touched a Motorola. But I do know he said he would let me know what is what.

I've made conventional repeaters in this manner before, so the matching and desense issues I have dealt with in the past and shouldn't be a problem for me. That is the fun part.

 

[BMDaug]

The console option is ideal, but again, due to locations it would require a mast mounted antenna at either site which currently no one wants to pay for. Luckily the systems are on different bands entirely UHF/800, so desense shouldn't be an issue. Tho spacing antennas is always ideal in any case. I plan on also using yagi's.

Am not certain what radio exactly is going to be supplied from the other county. I had thought he said an XPR2500. but I know he did say he would have the proper accessory cable for it for PTT and such. I've been living in the Harris / Kenwood world for so long, been a while since I touched a Motorola. But I do know he said he would let me know what is what.

I've made conventional repeaters in this manner before, so the matching and desense issues I have dealt with in the past and shouldn't be a problem for me. That is the fun part.

It’s the same idea… I’m installing a pyramid SVR250 to cross and from conventional analog VHF to a P25 trunking system and it still works the same way… The pyramid people even say that if capacity on the trunking system is not an issue, it’s best to run their repeater in conventional mode, where you just hold PTT for a couple seconds to allow the radio to acquire a voice channel, and then begin talking.

It sounds like you have tried to account for the system malfunctioning and using a separate TG is a good plan. Still, set the CCT short because you are still using up site resources when the radios are keyed up so there is still potential to impact safety if another officer can’t get a channel grant.

Make sure the radios can be inhibited by dispatchers in case they need to be remotely shut down. Read specs about the audio in and out of the radios to make sure that levels being produced are appropriate for providing full deviation to the transmitters and make sure that the logic is going high or low appropriately to trigger PTT.

I’m glad you are crossbanding. That takes a few hurdles out of play.

Good luck!!

-B

 

[jeepsandradios]

An XPR is not a P25 Trunking radio. I'm fairly confident what systems your patching together and I am still confused why neither agency can afford to add a radio and an antenna to a console site. Also I hope this isn't being done in some garage and plans are to put it in a Public Safety facility. I think some conversations with the parties involved need to happen more.

 

[Firebuff880]

First off the XPR-2500 is a MOTOTRBO DMR radio not a P25 radio.

Second, having done this as a ComL many times I would also suggest you use the Console patch, but given your agency is still on EDACS which died many years ago, I guess I can see the $$ issue. I would look for a pair of JPS Interop NXU-2B or RSP-Z2 units and put one in each center and then use an Internet point to point connection to link them.

Then if a problem occurs, someone on ether end can kill the connection.

 

[Roadwolf]

The JPS Interop NXU-2B was suggested by myself actually. But that means getting a port opened from the IT department and they don't quite understand how radio systems work / what this would be for (they want to remove the radio system entirely and go with 5G and Cisco wifi cell phone service instead). They would also want to set up a whole new VLAN just for this item I believe, as they likely wouldn't trust this strange object on existing VLAN's. Plus their network reliability is much to be desired. That being said, if I could manage to get them to open a network drop on my end, I would rather go this route.

So many fingers in the pie that it gets annoying sometimes. lol

 

[BMDaug]

@Roadwolf Since the obvious plan is to put this inside the coverage area of both systems, and that place is not dispatch, where is that exactly? Is it somewhere secure with backup power? Is it somewhere that you can mount antennas outside? Just things to think about…

-B

 

[Roadwolf]

@Roadwolf Since the obvious plan is to put this inside the coverage area of both systems, and that place is not dispatch, where is that exactly? Is it somewhere secure with backup power? Is it somewhere that you can mount antennas outside? Just things to think about…

-B

Yes we have a secure location in an overlap area with backup power. The coverage is such at this site that no mast mount antennas are needed. It is not a radio site, but a location with other comms equipment which is secure.

 

[Roadwolf]

Hmm I think this thread helped, as I realized I could likely run a 4-wire console patch to that site from the main site where the radio system lives, over an existing multiplexer which is currently just used for telephone. But it is also capable of having channels configured for 4-wire. So perhaps this will work out in a more proper manner afterall.