primary vs alternate control channels

[WA0CBW]

Yes as each control channel is a different repeater (as well as voice channels).

 

[eorange]

Ahhh, gotcha. Didn't understand that part - thanks.

 

[GTR8000]

Ahhh, gotcha. Didn't understand that part - thanks.

Every frequency in a trunked system has its own repeater (in the case of a simulcast system, multiply each frequency by however many subsites there are...a 10 subsite simulcast system with 10 frequencies has 100 repeaters in total). The control channel is obviously on the air 24/7, which means those repeaters are transmitting constantly. Allowing the control channel to roll distributes the transmit time among two or more repeaters, theoretically reducing wear and tear on them.

This was more of a concern with older equipment, such as Quantar repeaters on Motorola 3600 systems, which is why some of those systems tend to roll their control channels regularly.

Newer hardware, such as the Motorola GTR 8000 series linear repeaters, very rarely roll control channels unless there is an issue that forces them to roll. This is true with most modern P25 systems running on the newest generation of hardware.

 

[SCPD]

Thank you guys for info on this subject.

 

[eorange]

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Agree, great info - thanks!

 

[mmckenna]

Really? I'm not doubting you since you sound like you're in the biz, but do CC changes (from what I've seen, around 1 MHz or so) really help extend the equipment life?

I could see there being a more noticeable effect when switching across entire bands.

I am in the biz...
I have 5 800MHz pairs assigned to my system. That's 5 repeaters, 5 amplifiers. I can chose to set up the system however I want, even leaving the control channel on 1 repeater indefinitely. While it's true that newer equipment doesn't necessarily need this, I chose to do it anyway, and for a couple of good reasons:
1. It spreads the stress out across the system. No reason to beat the heck out of one repeater and not the others.
2. It forces each repeater to work hard for one day out of 4. Knowing that any of the 4 repeaters are running properly every couple of days is a good way to keep eyes on the system.
3. I have the system set up on two different battery banks, by choice. Each battery bank has it's own group of power supplies that run the system and keep the batteries float charged. By keeping the control channel on one repeater and one power system, it needlessly stresses those, also. Knowing I can go into the system and kick the channels over in a power outage is a handy way to spread the load on the batteries.
4. I just prefer to do it that way, and because it's my system, I can.

Same reason I check the back up system every morning. You need to know it's all working correctly if you expect to rely on it in an emergency.
My system is not P25, it's a Kenwood NexEdge system, so it's a bit different. I'm not convinced that beating one repeater on a P25 system is the best choice. Just because some manufacturers do it that way doesn't mean it's any better or worse than others.

 

[GTR8000]

I am in the biz...
I have 5 800MHz pairs assigned to my system. That's 5 repeaters, 5 amplifiers. I can chose to set up the system however I want, even leaving the control channel on 1 repeater indefinitely. While it's true that newer equipment doesn't necessarily need this, I chose to do it anyway, and for a couple of good reasons:
1. It spreads the stress out across the system. No reason to beat the heck out of one repeater and not the others.
2. It forces each repeater to work hard for one day out of 4. Knowing that any of the 4 repeaters are running properly every couple of days is a good way to keep eyes on the system.
3. I have the system set up on two different battery banks, by choice. Each battery bank has it's own group of power supplies that run the system and keep the batteries float charged. By keeping the control channel on one repeater and one power system, it needlessly stresses those, also. Knowing I can go into the system and kick the channels over in a power outage is a handy way to spread the load on the batteries.
4. I just prefer to do it that way, and because it's my system, I can.

Same reason I check the back up system every morning. You need to know it's all working correctly if you expect to rely on it in an emergency.
My system is not P25, it's a Kenwood NexEdge system, so it's a bit different. I'm not convinced that beating one repeater on a P25 system is the best choice. Just because some manufacturers do it that way doesn't mean it's any better or worse than others.

Great post. I love your thought process, and I agree that I'm also not sold on the idea of running a single repeater dead keyed 24/7/365, no matter how robust the manufacturer claims it is. If for no other reason than the one you stated in #2, I agree with that logic. It's always better to deal with a repeater failure on a quiet sunny day than it is during a disaster, so exercising them daily should uncover any issues that might go unnoticed if they sit idle for weeks or months.

 

[mmckenna]

Great post. I love your thought process, and I agree that I'm also not sold on the idea of running a single repeater dead keyed 24/7/365, no matter how robust the manufacturer claims it is. If for no other reason than the one you stated in #2, I agree with that logic. It's always better to deal with a repeater failure on a quiet sunny day than it is during a disaster, so exercising them daily should uncover any issues that might go unnoticed if they sit idle for weeks or months.

Exactly. This sort of -leave it until it fails- attitude does work. If the recent failures in Detroit were not enough to drive it home, I could work down the list.

Testing of the back up system is usually forgotten about, at least until it's too late. Some of the shops that maintain these systems are verging on criminal negligence. Why they are not brought to task on this stuff is beyond me. I guess to many agencies like to just write a check and hope that the system gets properly maintained. I just can't comprehend that attitude, especially when it comes to public safety systems.

 

[hitechRadio]

Every frequency in a trunked system has its own repeater (in the case of a simulcast system, multiply each frequency by however many subsites there are...a 10 subsite simulcast system with 10 frequencies has 100 repeaters in total). The control channel is obviously on the air 24/7, which means those repeaters are transmitting constantly. Allowing the control channel to roll distributes the transmit time among two or more repeaters, theoretically reducing wear and tear on them.

This was more of a concern with older equipment, such as Quantar repeaters on Motorola 3600 systems, which is why some of those systems tend to roll their control channels regularly.

Newer hardware, such as the Motorola GTR 8000 series linear repeaters, very rarely roll control channels unless there is an issue that forces them to roll. This is true with most modern P25 systems running on the newest generation of hardware.

P25 system here has been on the same cc channel for 5 years 24/7. GTR8000's. And has never failed. Heck none of the VoiceCchannel amps have failed in that time either.

Motorola tends to under rate the power output of there transmitters. Example: Rated 110 watts the amp is actually capable 225watts. So at full rated power 110watts it is just loafing along.

Had an MSF5000 data station that ran full rated power for 4 years with no PA failure (and no fans by the way) and was replaced by a Quantar after upgrade that ran for another 5 years at full power with no PA failures. Until the data system was completly removed from service. Maybe it was just luck, but I dought it. A proper PA design can last.
There are other manufactures out there besides Motorola that make some long lasting PA's. I have heard Cresend and TPL make some good PA's but I have no experiance with them.

 

[mmckenna]

P25 system here has been on the same cc channel for 5 years 24/7. GTR8000's. And has never failed. Heck none of the VoiceCchannel amps have failed in that time either.

Yup, I hear ya. We had MSF-5000's that ran for 18 years on a SmartNet system, and they did really well. Good solid repeaters. As they aged, we started having all sorts of issues with them. 18 years was way past their intended life span, of course, but that tends to be the way we roll.
As they neared their demise, we had issues with them wandering off frequency. We didn't always catch that when they were working as voice channels, but we would when they were control channels.

I understand what you are saying about the P25 systems. A good system, properly designed AND maintained should run for a long time.

I replaced that system with a NexEdge trunked system running the Cressend amps, and the system has been flawless since we fired it up. Hopefully we won't run this one for 18 years before replacing it.