Batboard

I'm working on a possible LTR solution for a customer here. The system is a UHF 5 channel regular LTR (not Passport). Subscriber sets are HT1250LS and CDM1550LS.

The only LTR experience I have is with 900MHz GTX sets, so I'm going to assume they are programmed similar. The customer requires about 12 talkgroups.

The groups are balanced across the system so that groups don't all hog the same home channel. (Groups 1 and 2 use channel 1 as home, 3 and 4 use 2, and so on). Anyhow, the customer requires an "all-call" group that all radios are able to receive, but any replies would take place on their own selected group (so the only traffic on this "all call" group would be from the dispatcher).

I messed around with a GTX set and it seems a Universal group would do this, however it seems that it only works on groups in the same access block and therefore the same home channel.

Talkgroups are as below:

1-01-150
1-01-200
1-02-150
1-02-200
1-03-150
1-03-200
1-04-150
1-04-200
1-05-150
1-05-200
1-05-210
1-05-220

The last two groups see little traffic which is why they are on the same home repeater.

Aside from having another radio programmed with 5 "all call" channels, one for each home channel, is there another way to address all radios on all groups at the same time?

Thanks for your help!

note: I use the word "channel" here to indicate a logical talk group or whatever...the equivalent of a conventional carrier squelch channel to the user:

We recently set up an LTR system and have learned a lot since then.

One customer wanted a main channel and some admin channels to talk to his straw boss, etc. We gave them to him on a different home repeater than his main and immediately regretted it. The LTR data is 300 bps and so in order for it to "scan" it has to be switching freqs and then decode the data stream long enough to tell what channel(s) are active where, etc. I can't remember the exact number but I think in a worst case scenario it can be several seconds.

It seems from the programming of my radios (Kenwood) that Johnson, when they did LTR, intended that all units from a certain company be on the same home channel. That way radios can be set to recieve many different "channels" without switching frequencies unless the wanted information happens to be coming through on a different freq. In that case the data will come through on the main freq telling any radios that are listening what freq they should switch to.

I hope this makes sense to you. I am pretty tired right now.

Birken

Most of the talkgroups are relativly high traffic. Is there any disadvantage or issue with having a number of busy groups sharing the same home channel? I would have figured that if 10 or so heavy traffic groups programmed with the same home channel would have made for longer channel access times. Not only that, but having them all on one home channel would put a very heavy (probably constant) load on whatever channel that is, so some load balancing would be an order.

Also, to put an "all call" group, would it be better to set the RX range from 120 to 121, then TX on 120 and just the dispatcher able to TX on 121, or would I be better off using 121 as a Universal group?

My apologies for all the questions, but I'm trying to learn as much about LTR as I can!

I know what you're saying...when I installed a small 2-channel LTR system, I put the two different hotels which were sharing it on different Home channels, to avoid having a single channel in use 90% of the time & the second one in use only 10% of the time. Since they were GR1225 repeaters, it made sense to spread the load. The load-sharing was accomplished, but the big disadvantage was Universal ID's cannot cross over between different Home channels. Originally it wasn't a problem as each hotel had their own, but later on they wanted the capability of making announcements to both hotels, and we had to go with a scanning arrangement. Didn't find the big delays that Birken talks about, it actually worked quite well...but the scanlists were small, two channels maximum.

If you're using continuous-duty rated repeaters, I wouldn't worry too much about spreading the load. You won't notice any appreciable difference in access time regardless of which repeater is chosen.

I don't consider the GR1225 to be continuous duty rated at 25-watts as Motorola claims...have had to replace too many P.A.s to believe it.

Todd

As far as the delays go, you have to consider how the LTR system works. A radio listens to its home frequency for its ID at all times. If its ID comes through on the home freq then it opens squelch, otherwise it tells the radio what freq to go to. The data stream is continuous telling radios with this ID to go to that channel and radios with another ID to go to another channel, etc. and at 300 bps that can potentially take some time. It depends entirely on the workload too and some radios when they scan check only 3 IDs on the scanned channels before assuming they are not wanted on that channel, others will check as long as it takes to rule out their being wanted which, again depending on load can take a good long time.

Our customer with several channels was also making very short transmissions that were getting lost; he may also not have been waiting for the "go ahead beep" but he would say something like "Hey Kev" real fast and the other radio may not have even scanned in that short time.

Another annoyance we found was with a company who wanted to scan some conventional channels as well as their own home LTR channel; the radio will do it, but it will not do priority lookback to an LTR channel because of the amount of time required, much more than the .3 to .5 second I usually set to avoid chopping the scanned audio up too bad so they don't even allow it. We told them they would have to get a scanner to make that happen, because otherwise they were going to miss calls on their own channel.

If you keep all the GIDs in the radio on the same home channel, or in the same "zone" especially, then the radio will not have to go frequency hopping at any time to determine if it is wanted, it only has to continuously monitor the data stream for any of its GIDs, which is what it does anyway.

Birken

Well, we're a 3rd party supplier, buying bulk air-time from a much larger company, so unfortunatly we don't have the ultimate power to decide how things get done. That said, I've got a very good working relationship with the owner of the system and they've given me quite a bit of freedom and are open to suggestions so I'm pretty hopeful!

The repeaters are all Motorola MSF5000 high power stations with some Kenwood LTR controller (SmartSite or something like that I think). My reasoning for the load balancing is because of the nature of the provider. I highly doubt they would be willing to tie up 3 or 4 repeaters with just our traffic, even though an MSF can be keyed down forever (I've heard of one that was dead keyed for 2 weeks at 100+ watts with no damage).

It sounds to me like the best way to do it would be to put related groups on the same home repeater so either a Universal ID can be used, or a range of RX.

One further question. On a GTX set, there is a setting for TX Inhibit Low and High IDs. The best I can tell, these are used to prevent the radio from transmitting when those particular groups are transmitting. My thoughts are that if we use either a Universal group or a range of RX, we could program whatever the "all-call" group is into the TX Inhibit field so that nobody else can talk on the group except dispatch, and it would force everyone to be in RX mode when the all-call group is in use.

Sorry for all the questions, but I really want to learn as much as possible about LTR as it looks like sometime in the future we will look at owning/operating our own system. Are there any decent documents that explains the details of programming/operation of an LTR system?

Many thanks again to everyone's input!

Inhibit High/Low gives a transmitting user a 3-second period after releasing the PTT to decide if he wants to transmit again. During this 3-second period, the system prevents a receiving radio from transmitting. This occurs only if both the transmit and receive radios are on a talkgroup ID that is within the bounds of the radios' Inhibit High and Low IDs.

bellersley wrote:Sorry for all the questions, but I really want to learn as much as possible about LTR as it looks like sometime in the future we will look at owning/operating our own system. Are there any decent documents that explains the details of programming/operation of an LTR system?!

There are about 3 major documents out there on the internet describing LTR operation, many copies of the same thing floating around with different titles and headings but if you do a search you should be able to come up with them, they are not hard to find.

Birken