Crossbanding question. Can it be done?

601 · Post by **601** » Sat Apr 07, 2007 9:22 pm

Hello all, i'm looking into some ideas for my 1st aid squad that i'm on. I came up with one that i'm not sure is even possible, but maybe someone on here can steer me in the right direction?

We currently are operating on a UHF T-band Motorola Type II SmartZone system. We are also licensed on a VHF EMS channel. I would like everyone to be able to carry 1 portable to be able to communicate, as our county is still dispatching on VHF, Money is tight, and the lowest radio Motorola is offering us (They built the system directly) is the XTS1500. With our money issues, this is preventing us from being able to have reliable communications at all times.

Is it possible to hook up a mobile repeater to our rigs to crossband VHF with UHF trunking? We are using analog astro mobiles in the rigs. This would allow our members to be able to use our county channel to call for mutual aid and medivacs directly while out of the rig if necessary, and be able to communicate with our town dispatch. Or does anyone else have any idea what we could do? We were forced into this system (that coverage sucks with btw, 4 voters across town and it still comes in scratchy) and are running out of ideas.

Any help would be appreciated. Also, we're only looking for suggestions right now, we will be applying for all proper licenses once we figure out what we can do

thebigphish · Post by **thebigphish** » Sat Apr 07, 2007 10:26 pm

Did the exact same thing, but we brought in a VHF / UHF / UHF LTR setup. The system will work, EXCEPT, when there is traffic on the TypeII system, the radios on the other side of the link will not know....will not get inhibited....and can theoretically key up on their portables while the system is busy...thus causing a situation where they will not know the system is busy, and their TX will go nowhere...

You will have no way of knowing when it is clear to transmit....the Type II will do a nice job of simulcasting out onto the VHF stuff, but if the system is busy on a tower, or if the radio is taking some time to key up, you will have a dead link... be cautious.

Post by **wavetar** » Sun Apr 08, 2007 4:35 am

thebigphish wrote: but if the system is busy on a tower, or if the radio is taking some time to key up, you will have a dead link... be cautious.

Yes, that is a possibility when cross-banding with trunking. Futurecom units somewhat get around this, by sending out a series of beeps to the conventional side after it unkeys, if the trunked side didn't go through properly. So, you find out after the fact that the trunked units didn't hear you, but at least you'll know & can repeat the message.

However, Futurecom set-ups aren't cheap, and require to interface to either an Astro Spectra W4 or XTL5000 W4 in order to work on digital.

Todd

RKG · Post by **RKG** » Sun Apr 08, 2007 4:35 am

We have done this using a KR Nida box. Works bi-directionally (i.e., traffic on any channel (we actually can link up to three) is heard on the others. Only limitation when one of the channels is trunked is that subscribers who key on the non-trunked channel do not get the "talk permit" tone, and so have to be trained to pause before speaking. We used three MCS2000 as the mobiles.

Bruce1807 · Post by **Bruce1807** » Sun Apr 08, 2007 4:36 am

We do something a bit similar but opposite and do it through the CEB
We have a couple of marine channels (one 16 channel MTR for different channels, 1 single channel MTR for channel 16 and a maratrac for channel 17.
These are permanently patched on the CEB to talkgroups.
The system works great in that our marine police only need to carry one radio but as stated the busy side can be a problem.

Whilst our units carry SZ radios , their keyups are controlled by the system whereas any one can key up on a marine channel anytime and channel 16 is just rampant with our Spanish speaking friends who forget to switch.
it would be cheaper than changing all vehicles (depends how many you have.

The idea would be simply to patch your VHF and UHF together.
now you already have the transmitters and if you colocate txers anywhere then it should be easy.

Give a little more explination on the local and county system and it should be easy and if there are common sites maybe no physical cost just a little programming of TenSr's , the CEB and the SZ.

jackhackett · Post by **jackhackett** » Sun Apr 08, 2007 7:08 am

We did a system a while back using Pyramid vehicular repeaters, they use a VHF portable to talk through a trunking mobile. They're kind of a pain to use, IIRC you have to key up for second, wait for a talk permit tone, then key up again and talk. Takes a bit of getting used to, but it's an option.

601 · Post by **601** » Sun Apr 08, 2007 7:41 pm

Thanks everyone for the input!

Here's a few points:

The talkgroup that we're on is only used by EMS. At most, we have 4 rigs out at a time, most of the time we only have 1 or 2 out on calls. Radios are barely used, so I believe talking over someone won't be a problem.

Our VHF channels we use are all simplex, so nothing further would be needed on those.

Does anyone have any links to the equipment mentioned that I would have to use to set this up? I need some info and pricing to present to the board to see if this may be an option they're willing to consider. I found Pyramid, just hoping for some more info.

Thanks!

RKG · Post by **RKG** » Mon Apr 09, 2007 4:26 am

http://www.krnida.com/products.htm

aaknitt · Post by **aaknitt** » Mon Apr 09, 2007 12:58 pm

Just to clarify, the problem people are warning you about isn't that you'll accidentally "talk over" one of the other EMS units on the trunked system. The problem is that if the trunked system (the whole system, not just your talkgroup) is "busy" when you try to key up on the VHF portable, you won't know it.

On a normal trunked system, you push the PTT button, and then wait until the radio beeps before talking. If the system is busy (all frequencies are in use), you'll get an error beep letting you know to try again.

When you crossband into the trunked system, you won't get the beep to tell you when you can start talking, so you just have to train people to pause for a second, and hope that the system isn't busy. Some crossband devices (like the one mentioned above) will notify you that the system was busy after you unkey, and you can then repeat your transmission.

I hope that makes some sense.

Andy

jackhackett · Post by **jackhackett** » Mon Apr 09, 2007 7:03 pm

I can't help you with prices, but I can tell you one other thing about the Pyramid units, they take a little work to set up. The alignment procedure calls for using two service monitors, they need to be programmed (requiring software and cable), and the radios need to be programmed to interface to them, so make sure you deal with someone equiped to handle that.

601 · Post by **601** » Mon Apr 09, 2007 8:05 pm

Yep, I didn't plan on doing this myself. No way, I know nothing about this type of equipment, and I'm not destroying a brand new township owned mobile radio. The cost of the install would be included with the price. We have a radio shop that should be able to do a professional install.

If they go for this, we will also require training on how to use the system before we even issue them a portable, something I wish we would do with everyone before they get to use the radio.

mr.syntrx · Post by **mr.syntrx** » Mon Apr 09, 2007 8:46 pm

SmartBridge SB-100

http://www.rstradio.com/prodinfo.html

Used with great success on my state's UHF SZ OL system.

thebigphish · Post by **thebigphish** » Mon Apr 09, 2007 10:33 pm

Is the option of adding a trunked mobile to the dispatch center's CEB completely out of the question? Instead of putting all the effort into the field, why not add a piece on the other side of the system? If the system administrator is open to suggestions, why not try?