Link from Trbo system to Passport system

[tdats]

I have to somehow get one of our schools running on a Trbo system to be able to talk to one of our Passport talk groups in the event of an emergency. The school's portables on the Trbo system will have an additional TG added to their radios for this emergency channel. The Passport system does not cover that school building.

My thought is 2 radios, 1 on each system with some sort of interconnect between them. I am looking for recommendations on how to accomplish this. Most of my experience connecting channels is at our county on short term emergency sort of basis using either an ACU-T or a Codespear system. In the short term, those work well, but seem to be very overkill for this situation.

I have a few CDM1550's on the passport system available right now, and a facility positioned to be able to get into both systems.

Any suggestions on the interconnect, or other ways to do this?

Thanks!
Tim

[Bill_G]

In another post you said you use XPR6550's with the Scholer-Johnson boards installed so you could use the Passport system. But, apparently the system doesn't have enough building penetration to work well. So, now you want to try to crosspatch the two systems. Ew. Trbo mobiles have a CD line, but I don't know if it functions in digital mode which you obviously use since you're talking about talk groups. The Carrier Detect / COR line is necessary for this work correctly. You could try VOX, but it will be disappointing. You'll need an interface that has programmable delays to kill the ping-pong effect of two trunking systems re-keying each other.

Reading through the Telex IP223 application note on interfacing to a XPR4550 indicates it can be done. They show a connection to the XPR CSQ DET line, but they don't say if it functions in analog mode only. They do discuss setting the delays - very important. An IP223 with the latest firmware will let you crosspatch port 1 to port 2 (unlike earlier versions). So, you may be able to accomplish this with a Telex IP223 - a CDM on one port, and a XPR on the other. You'll have to roll-yer-own cables, and do the programming.

And, you'll have to separate the two antennas by quite a bit to prevent mutual interference since they will be in the same band. That will be an important hurdle to jump.

[RFguy]

XPR4350/4550's COR line DOES operate in digital. They didn't in early version FW, we had to pull COR from the audio amp enable line. After about year 2 or so, the FW changed such that the rear pin COR now functions as a TG detect.

[Bill_G]

That's good news. It will be easier to do with a positive rx indication. I don't think I would try this with a plain old RICK to make a bi-directional repeater, but it might be worth a try. I have visions of it ping-ponging driving users mad. I also have visions of it being slow to pass audio as each direction waits to get a talk permit. I expect a lot of chopped conversations.

[escomm]

That's good news. It will be easier to do with a positive rx indication. I don't think I would try this with a plain old RICK to make a bi-directional repeater, but it might be worth a try. I have visions of it ping-ponging driving users mad. I also have visions of it being slow to pass audio as each direction waits to get a talk permit. I expect a lot of chopped conversations.

I'd expect the audio to be slow to pass because of vocoding. Two portables sitting a foot from each other talking simplex have a 200-300ms delay

[Bill_G]

That's good news. It will be easier to do with a positive rx indication. I don't think I would try this with a plain old RICK to make a bi-directional repeater, but it might be worth a try. I have visions of it ping-ponging driving users mad. I also have visions of it being slow to pass audio as each direction waits to get a talk permit. I expect a lot of chopped conversations.

I'd expect the audio to be slow to pass because of vocoding. Two portables sitting a foot from each other talking simplex have a 200-300ms delay

Yep. Patience would be paramount, and in an emergency, ain't gonna find that around.

I mentioned this project to our Trbo dude, and he kind of rolled his eyes. His suggestion is to have a Passport base in the office playing human relay during exercises and real events.

[tdats]

A base radio at the remote site might be the best answer for now.

We were both on the same Passport system, but the system operator is in the process of converting the system to trbo and converted them already. This remote school distinct was separate from our district (so it was not my problem), but this year they have been put under our district, our superintendent wants our same emergency communications procedures to work up there. (So now it is my problem)

Eventually we will also be trbo and on the same system, but I don't see that happening soon with how many HT1250's we have in service right now.

Good points about the ping-ponging. Never thought about that. I have never tried to link 2 trunked systems together, it's always been a conventional to a trunked. I know with our Michigan statewide system there are talkgroups linked into conventional stuff, but I have no clue what hardware they use to make something like that work.

[Bill_G]

It's not impossible. You just have to work out the bugs. That's why you need a magic box with delays you can apply to the xmit PTT and audio lines.

[Radioguy7268]

There's a guy selling a CDM to XPR cross-banding cable on Ebay for about $65. They work OK, audio quality is not great, but acceptable.
http://www.ebay.com/itm/RA-2TA-Repeater ... 1c22d6eed2

Delay is no more than the std. Digital delay built into Trbo, but I've only seen it done with Trbo cross-banded to conventional simplex. I guess the LTR/Passport keyup could add another few hundred milliseconds into the delay, but it would still beat a human repeater fixed to a desk with 2 radios.

Probably the closest thing you'll get to a plug and play for this kind of interface, without spending lots of time to re-invent the wheel.

[wavetar]

It's not impossible. You just have to work out the bugs. That's why you need a magic box with delays you can apply to the xmit PTT and audio lines.

We've used the IP-223 for this, cross banding a Motorola & Kenwood trunking systems with an XPR and an NX800. Once the proper delays are set, works great with no ping pong effect.

[Bill_G]

It's not impossible. You just have to work out the bugs. That's why you need a magic box with delays you can apply to the xmit PTT and audio lines.

We've used the IP-223 for this, cross banding a Motorola & Kenwood trunking systems with an XPR and an NX800. Once the proper delays are set, works great with no ping pong effect.

I have too. The assumption is you'll always get a talk permit which almost guaranteed on small systems. But, I have one tying a new 700M to an existing busy 800M system, and sometimes it doesn't always get through to the 800 causing a bit of consternation. Monitoring the 700 side, you can hear the BOOOONK from the 800 radio. I know what happened, but the users don't. 99% it works without a problem.

[wavetar]

It's not impossible. You just have to work out the bugs. That's why you need a magic box with delays you can apply to the xmit PTT and audio lines.

We've used the IP-223 for this, cross banding a Motorola & Kenwood trunking systems with an XPR and an NX800. Once the proper delays are set, works great with no ping pong effect.

I have too. The assumption is you'll always get a talk permit which almost guaranteed on small systems. But, I have one tying a new 700M to an existing busy 800M system, and sometimes it doesn't always get through to the 800 causing a bit of consternation. Monitoring the 700 side, you can hear the BOOOONK from the 800 radio. I know what happened, but the users don't. 99% it works without a problem.

Yep, that is always the caveat with these sorts of setups.