Batboard

My skull is unusually thick today... so I'm hoping someone can help me.

VRS's by Motorola, Pyramid, Vertex, etc., contain logic that has them shaking hands when they're on-scene with other VRS's so they don't interfere and lock up.

So why is there a problem if the officers leave them on and pass each other on the road? System in question is VHF CDM1250's with UHF VXR-1000's, main repeater is VHF conventional, UHF simplex frequency for use between VRS & portable.

Also, anyone know if a VXR-1000 can be left on and "parked" until it hears a transmission from one of the portables?

Thanks!

It seems simple, but the operation of these is a little complicated.

When a VRS is activated, it emits a single tone that tells all the other VRSs in range that it's on & operational. This is immediate and usually the last one activated is the one that functions at an incident. Also, the VRS is supposed to transmit in carrier squelch and the subscriber is supposed to transmit with a tone. If a VRS's connected mobile radio is receiving a signal and the VRS is also receiving a carrier squelch signal on the mobile relay frequency, then it will also go into stand-by but this is not immediate.

When your officers are riding around with the VRS already active (bad idea), there is no way for each one to know the other is there for a little bit. If they don't know the other is there and a subscriber initiates a transmission from their portable, they will cause both (or several) VRS equipped mobiles to transmit until they recognize that the other(s) is/are there. If, for some odd reason, your tech has programmed these to transmit on the same tone that the portables are using, then you will have all sorts of problems.

The question "if a VXR-1000 can be left on and "parked" until it hears a transmission from one of the portables?" is not clear to me. Are you asking will the unit sit idle and not repeating until it hears a portable & "wakes up"? If that is the question, then no - either it is on or off. Also, leaving the VRS on with the mobile on for an extended length of time when the vehicle is not running will result in a dead vehicle battery.


A situation that happened to me several years ago with a PAC-RT system was when I went to an EMS call on the roof of a papermill about 100' up. From that vantage point I was able to hit about five other unit's PAC-RTs located at various other parts of the city. It was chaos because the individual PACs were too far apart to detect each other, but from my high vantage point I was easily able to reach the other PACs. Even with a 1 watt HT90, line of sight is a long way at 100'.

Sorry for the weird questions, I'm not that experienced with VRS setup. But I do find it very interesting.

The VXR-1000 software allows programming the VRS for transmit with tone (or DPL) in addition to CSQ, depending on the master/slave mode that is selected. Could it be that the VRS can transmit and receive on U1 with different tones, or is the VRS required to transmit in CSQ? (Obviously the portable radio will be vice-versa with the tones on U1.)

I understand that if both the VRS and the portables are transmitting with the same tones that we could have lockup issues if a portable gets keyed down before the VRS's have sorted out who's master. Apparently this handshaking is conducted at very low power levels if the VRS's can't find each other while they're approaching on the highway with enough time to sort it out before the chaos ensues.

The question about the parking was more or less just as you re-stated. There are many things an officer has to do when they get out of the car... remembering to turn this and that on, remembering to grab what they need for their stop. It was just a thought so that there was one less thing to worry about.

Thanks for the help!

So, how about a situation where each of the Pyramid VRSs is keyed with a different PL? My FD operates in three mutual aid districts, each of which uses a different band! The department operates primarily in UHF and all apparatus have a UHF HT per seat and all officers have an assigned HT. The problem we want to overcome is how to operate in other districts. At first we had one VRS, in Engine Three, on a pair of VHF Kenwoods and every UHF portable has the VRS input in it. When arriving on the scene the operator is supposed to tune the VHF head to the local frequency and turn on the repeater. This way every portable can use the local frequency through the repeater. Now I have a request to put a VRS in Rescue One. The plan is to have the VHF radios permanently tuned to the local ambulance frequency. Then, in theory, any EMT can communicate with the ambulance through that VRS. The plan was to use a different PL in the two VRSs so both units could be on the same scene but talking out on different frequencies. Does anyone see any obvious flaw? And, if we do that why could we not wire both repeaters to the on position so that every UHF portable could select one of them to talk out through? In other words, we would be doing the very thing everyone discourages which is to leave the VRSs turned on.

Yup, I see a big flaw...

If both VRSs are operating on the same UHF frequency but a different CTCSS you will have a problem when the ambulance company frequency is active at the same time as the VHF fire frequency. Either one VRS being active is going to cause the other to go into standby, or both will be transmitting and all you will hear is a nice heterodyne. You are going to want to obtain a different frequency for the VRS that is being used on the ambulance company frequency.

If your engine is the only unit that has a VRS, then there probably won't be a problem with leaving it on. The problem comes when you have several VRSs on all the time.

I forgot to mention another scenario to the OP - Lets say one of your officers is out on a traffic stop - another officer happens by and he has is VRS on - the two VRSs “shake hands" and the VRS of the officer on the traffic stop decides to go into standby. The mobile officer goes on down the road. Meanwhile, the perp pulls a gun & the officer on the traffic stop gets on his HT to call for back-up. His VRS is in standby and nothing goes through. Yes, his VRS will eventually recognize that it is alone & turn itself back on, but in this situation, the officer would probably only get ONE chance to call for help, but that call would go unheard.

The VRS system is great, but you have to be very careful in how it's used. If you are doing anything weird to operate it, it's probably going to let you down.

Someone correct me if I sound like an idiot.

The only way I think we could get away with everyone being able to leave their VRS's on all the time is to have give each HT it's own uplink frequency. And then we'd have to leave the HT's with the cars all the time. But then if an HT fails, the car will be out of service, too.

Unless we have HT's with at least enough channels so that all the uplink frequencies can be programmed in. Then all you have to worry about is someone bumping the HT's channel selector off-channel. And licensing a frequency for each car.

Now we could also use one uplink frequency with a PL/DPL for each car. If one keys up and then another keys up, they still will interfere, but will it be any worse than two mobiles keying up?

But then this is complicating matters. Not that VRS configuration isn't.

So thinking about my earlier question and the following discussion, does this make any sense:

If the VRS's and portables are all programmed to transmit the same PL/DPL it seems like if a portable keyed up before the VRS's decided who's the boss, then the portable would key up several VRS's. And of course it would sound like garbage due to the multiple-unit interference. At some point during this, the VRS's would pick their boss, and the slave VRS's would stop responding to portable radio input. When the portable radio unkeys, only the boss VRS unkeys. The other VRS's which have stopped responding to portable input are left transmitting, which is only stopped by turning off the offending VRS's.

And yes that is a bad scenario, but important to consider, AI4UI.

If a VRS is activated when the second (3rd, 4th, 5th...) officer arrives on scene, it sends a signal to the other VRSs & it automatically becomes the VRS that is operational - all the others by design will go into standby. The problem comes from that signal not being sent and then there will be a few seconds of heterodyne until one of the VRSs becomes the boss. I've heard of several different passive things being done to activate a VRS. Talk to your fleet manager and see if there can be a signal obtained from the car when it is placed in park. In fire trucks the airbrake switch is an excellent place to obtain a signal. The VRS's that I've used have been in conjunction with a portable charger - when the radio is in the charger, the VRS is off, pull out the portable and the VRS comes on.

You have quite a quandry - leave the VRSs on all the time and you run the risk of them interfering with each other. Have a manual activation system, and you run into human error - an officer forgets to activate their VRS and then they get into trouble and can't call for help.

Having each VRS on it's own frequency would be a nightmare. Not only would you have to pay to obtain & license "X" number of new frequencies, but then you would have to keep track of which one was where. Plus, if all of your officers were on their own frequency and they chase a perp out into the woods (or into a dense building) far enough away that they could not reach back to their cars, they wouldn't be able to talk to each other because they're on different frequencies.

Alright this is what I've learned so far in easy-to-digest chunks:

• Keep the VRS off while the officer is in the car. Automatic switches could be a good thing.
• The simplex uplink frequency (SUF) should be on a different band that the main repeater.
• All VRS's and portables should be on the same SUF.
• The transmit PL/DPL should be the same for all the VRS's.
• The transmit PL/DPL should be the same for all the portables, but different than the VRS transmit PL/DPL.
• The time between handshake checks should be as short as possible.
• Don't push it by doing anything weird.

How does this sound?

2112, I like your method of regurgitating in small, easy to digest pieces. I'd like to go all the way back to ai4ui's original extremely helpful replay and do something similar. I first want to develop some definitions starting with your use of the term uplink frequency.

As I understand the system, and I am referring specifically to a Pyramid VSR, to transmit audio, the portable in your hand transmits on the VSR's frequency, using a unique PL. The VSR, via a wiring harness, keys the attached transceiver and operates it exactly as an attached mic would. In this case, only the specific VSR would respond in any way because of the PL code. A second portable, using the PL of the second VSR could operate at the same time although there certainly will be some amount of heterodyne action between the portable's tranmissions but that is always the case with neighboring communities using a common frequency but different PLs. Correct so far???

Given that the two VHF radios attached to the two VSRs are on completely different frequencies both transmission should function exactly as they would if the two operators had hardwired mics.

I can see a problem with received traffic, however. In this case the VHF radios would receive the traffic and then key up the Pyramids which would attempt to transmit to the two portables. I can see this is a problem with no obvious resolution.

As to the VSRs communicating with each other upon activation, how is that done? If they use the frequency you've programmed into them and each receive-side is looking for a different PL these two particular VSRs shouldn't see each other, correct??

In addition, although I haven't tried it, from the documentation it appears the VSR only sends the "here I am" code on on activation. If both were on all the time, would they acknowledge each other?

Yeah, I learned the value of scan-ability in writing late in life... it sure has saved me alot of heartache.

The way you put it is different than the way I put it: In my version, the VRS's all transmit the same tone (let's call it T1) and listen for the same tone (let's call it T2). T1 and T2 are different to avoid pre-handshake lockups. The HTs' tones are programmed to the reverse of the VRS's... they transmit T2 and listen for T1.

In this system, any handheld can use any VRS.

In your version, it sounds like you want tones for tx/rx to be the same for each VRS-HT pair, with each pair using a different tone, but each pair using the same SUF. In this system, any handheld can only use on VRS.

I think for this to work you'd have to disable handshaking. If you left handshaking enabled, when two VRS's rolled up to a scene, they'd pick a boss and the other one would go into standby. Then someone wouldn't have portable coverage.

And the portables wouldn't be able to talk to each other directly.

Another problem is when someone keys up their HT, all the other VRS's on a scene will be re-transmit the main repeater's output... causing everyone else listening on their HT's to hear garbage. And, because of all the VRS transmitters transmitting at the same time on the same frequency as the original HT, those listening to the main repeater directly will hear heterodyne garbage. Sounds like it'd be a big mess.

We could try separate uplink/downlink frequencies between the HT's and VRS's. Even so, when all the VRS's retransmitted the repeater's output, the HT's would hear garbage. And the portables still wouldn't be able to talk to each other.

So, IMHO, it doesn't sound like a good idea. Unless I'm still being dumb, of course. Lol.

I have a good working knowledge how the Motorola PAC-RTs recognize each other, & I know that the Pyramids are designed to operate & cooperate with PAC-RTs and operate identically.

When the PAC-RT is initially activated it sends a 1 second tone burst (I want to say 1500 Hz, but I don't remember for sure) in carrier squelch - other PACs in the area on the same frequency respond to this tone burst by going into stand-by.

The idle PACs continue to monitor both the PAC frequency and the mobile radio channel (the PAC is fed unsquelched descriminator audio from the mobile and has it's own squelch ckt. for the mobile radio audio to determine channel activity). If a PAC notices that there is channel activity on the mobile radio, but is not receiving anything on the PAC frequency, then it will figure that it is by itself and it will turn itself back on. If a PAC in standby detects channel activity on the PAC frequency with the proper tone, and does not receiving anything from the mobile it will also figure it is by itself and then turn back on. This takes a couple of seconds and there is an opportunity to miss something important.

If a PAC is active, while it is receiving mobile traffic and is repeating, it will pause every second to listen to the PAC frequency for activity. This does two things - if the channel is tied up with co-channel interference, a stuck mic, or whatever, the portable can still force the mobile to transmit. Also, it is listening to see if there is another PAC operating. If it hears channel activity (CSQ or another CTCSS tone) on the PAC frequency then it will figure that there is another PAC operating in the area and it will go into standby mode.

So if you have two PACs (or Pyramids) operating in the same area on the same frequency (regardless of tone), but connected to radios operating on two different channels, there will be a constant battle as above - detecting activity on the PAC frequency, going into standby, receiving transmissions on the mobile but not detecting activity on the PAC frequency and turning back on, and receiving on the PAC frequency but not receiving anything on the mobile and turning back on. Having two PACs operating on the same mobile channel with one mobile scanning can cause the same battle.

What's important to note is that although this is how it is supposed to operate, it takes a few seconds for this to occur. There is a chance that someone won't get out at a time when they only have one chance, or they will miss something important.

You can try to do special stuff if you want like PAC frequency sharing with unique tones on different radio channels, but it is going to cause you problems at a time when you don't need any problems.

Robert

Robert, that is perfect information. What I want to accomplish is to allow any firefighter to "seize" the VHF channel selected in Rescue One OR seize the VHF channel selected in Engine Three. The Rescue would be tuned to the local ambulance and the Engine to a neighboring mutual aid frequency. It would appear the way to do this is to program each Pyramid with its own frequency. This would keep them from talking to each other.

We are dispatched as part of a UHF system and operate 90% of the time using UHF radios. We do belong to three mutual aid districts, however, and the two secondary districts are VHF, either high or low. In addition the local ambulance operates on VHF-high. The reason I'm striving to be able to leave the repeaters on is I can't depend on the Engineer, operating as part of a UHF system, to remember to turn on the repeater attached to his VHF system. This is particularly ugly with the Rescue since it needs to communicate with the incoming ambulance a high percent of the time. With unique frequencies we would be alright between our own two VRSs but if operate using only CSQ on both the Pyramid Rx and Tx side we run the risk of screwing up other VRSs that we might drive by if they are on one of our frequencies. Even with PLs on both Rx and Tx sides of the repeater, if the VRSs somehow communicate with each other CSQ, there may be no solution here other than to somehow remind the Engineers to turn them on when they arrive on scene. Seem right?

Sounds good. I would suggest to make the activation of the VRS passive.

Talk to your fleet manager and tell them you need a signal from the air brake parking switch. When we pull the parking brake on our engines, a light comes on on the dash that indicates that the parking brake is engaged.

We had to use this signal to turn off the opticoms (the traffic light control strobe) because our units would sit on scene at a vehicle accident and would force traffic lights to not cycle - not real popular with the folks on the side stuck on red. Now, when the unit arrives and the engineer pulls the brake, the opticom turns off.

You could use this same signal to control the action of your VRS - parking brake engaged, VRS is on.

Or, you could be a hard a$$ & write a policy then enforce it with progressive disipline. Give one guy 24 hours off without pay and I think it probably wouldn't happen again. Then again, I do work for some class A jerks and maybe my perception is a little skewed.

You sound like you've been around long enough to understand a policy won't fix this problem. Grabbing the "parked" signal is a great idea. All of our apparatus have a different emergency light pattern depending on whether or not they are in Drive. I think I'll have our mechanic give me access to that signal. Thanks!