System frequency allocation question...

[Q101ATFD]

So we're trying to figure out if our radio "problems" are that, or just a nuance of trunked radio systems... I'd like to hear from a practicing tech or system administrator, to see if Motorola is just blowing smoke our way. We've been having reports of some radios not receiving transmissions from others that are only 100 or so feet away - it's not garbled, it's just not received. I've never experienced it, so I can only go by what other users say. My thinking is that we are having more talk-requests than the system can handle...

We're on a P25 CAI system and I am in the understanding that only 16 transmissions can occur system-wide, the way this is setup - since there are only 16 licensed frequencies. Is that correct, or am I missing something here? I have been assured that the FD has 20 channels to ourselves - I'm sure that is a misunderstanding for talkgroups, but is it common for a city/county system to only have 16 frequencies? Am I reading this wrong, or does Cincinnati have 16 frequencies, and the rest of the system (site 101, AKA the rest of the county) has another 16 frequencies?

[N4DES]

A system busy scenario would not cause a single radio out of a group not to receive if they were on the same talk-group. Usually this scenario is caused by user error and the system is the easy fall-guy because it is difficult to reproduce.

As to your capacity questions, there are 20 licesnsed channels in the system for each County, but not knowing exactly how it is configured it is difficult to say how many talk-paths are available in each zone. My best guess would be 19 talk-paths and the last one is for control.

[MSS-Dave]

Sounds like a "nuance" of any half-duplex radio system.

I think you are experiencing desense of the receiver on the radios that quit. Your nearby transmit energy of another radio is probably stronger than the downlink signal of the repeater transmitter. On an analog system, you'd hear lots of noise, but on any digital system if the bit error rate exceeds the max for the vocoder to decode, it will just quit.

Dave

[Q101ATFD]

Okay - that makes sense. The system is setup so that the city and county each have their own set of 20 frequencies, as the DC was telling me. Like I said, I've never experienced the problem in 3 years, and it's most likely user error - but I wanted to rule out a system busy scenario. Thanks for the info!

[d119]

Is this regularly reproducible or is it intermittent?

Could be a bad channel in the system, etc.

This definitely bears further investigation, as it could be desense, but it could be something else as well.

What band is the system on?

[Q101ATFD]

Is this regularly reproducible or is it intermittent?

Could be a bad channel in the system, etc.

This definitely bears further investigation, as it could be desense, but it could be something else as well.

What band is the system on?

It is intermittent, at best - like I said, I've never witnessed it. I will say, however, that we get busy tones an awful lot, but that's usually when somebody else is transmitting. Sometimes we'll get the busy tone with nobody else talking, or trying to talk. We're on 800MHz - for now until we reband, but I don't think that'll happen anytime soon because we just spent $100,000+ on radio PM alone.

I'm not in the group officially looking into it, but I've heard that M was in town on two occasions to discuss it and other issues.

[d119]

It sounds to me like more of a system issue than a subscriber desense issue. You'd have to have a hell of a weak signal from the repeaters to have any sort of desense, and the radios would have to be awfully close together.

800MHz operates on a 45MHz frequency spread. When you talk on 821MHz to the repeater, others are listening to you on 866MHz. That's PLENTY of Tx/Rx separation to avoid desense in 99% of situations.

If Motorola is involved, you can bet there's something really wrong with the network itself.

[N4DES]

Is this regularly reproducible or is it intermittent?

Could be a bad channel in the system, etc.

This definitely bears further investigation, as it could be desense, but it could be something else as well.

What band is the system on?

It is intermittent, at best - like I said, I've never witnessed it. I will say, however, that we get busy tones an awful lot, but that's usually when somebody else is transmitting. Sometimes we'll get the busy tone with nobody else talking, or trying to talk. We're on 800MHz - for now until we reband, but I don't think that'll happen anytime soon because we just spent $100,000+ on radio PM alone.

I'm not in the group officially looking into it, but I've heard that M was in town on two occasions to discuss it and other issues.

Well you will always get a busy tone when someone else is transmitting on your talk-group and that is a normal setting. If you get it when nobody is talking it sounds like the system is at capacity or channels could be taken out of service automaticially by the system due to things like interefence. Unfortuantely for you as an end user, you will probably never know exactly what is going on unless someone demands the systems diags or a copy of the capacity reports.

I can say as someone who manages a 28 channel TRS that handles almost 10K subscribers of different diciplines, I never see a busy until a nice size storm is out in the atlantic and we just recently rebanded, which required up to bring the system down to 21 channels for almost a week, and never experienced a busy there either.

If /\/\ corporate is involded it is probably serious.

[Q101ATFD]

If you get it when nobody is talking it sounds like the system is at capacity

This is a regular occurrence city-wide, and my first thought was that the system was at capacity, but now I'm thinking that's not the issue since there are 32/30 frequencies. Our communications chief says that the M dealer stated that we've only been to 28% capacity, even during a huge wind storm a few years back...

I can say as someone who manages a 28 channel TRS that handles almost 10K subscribers of different diciplines, I never see a busy until a nice size storm is out in the atlantic and we just recently rebanded, which required up to bring the system down to 21 channels for almost a week, and never experienced a busy there either.

That's exactly what I was wanting to know - if you're TRS doesn't get busy, then ours isn't getting busy either. The union is upset and a lot of the firemen hate the radios - though there are a lot of us that aren't smart enough to let off the PTT for a few seconds after a busy tone and try again.

[N4DES]

Without seeing any kind of diagnostic or loading reports it is very difficult to say exactly what is going on. Whoever is blessed with managing the system needs to communicate better with the user base to explain what is occuring as I'm sure LE is having the same issues if it that wide-spread.

[RFguy]

If Motorola is involved, you can bet there's something really wrong with the network itself.

That is an ignorant comment and hardly adds value to the subject.

[borisf]

If Motorola is involved, you can bet there's something really wrong with the network itself.

That is an ignorant comment and hardly adds value to the subject.

Yay! I love recursive humor!