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Repeater lag

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#1
I guess this is the place to put this. On most of the systems I've used, you have to wait about .5-1 second after keying up before you begin talking in order to avoid being cut off. At a place I work for currently, there is virtually no lag between the time you keep up and the repeater starts transmitting. It's pretty much instantaneous. However, once you're done talking, the repeater stays on for like 2-3 seconds. Does this have anything to do with it not having any lag time? If not, why does it stay on for so long? This is on a VHF conventional analog system, btw.

Thanks.
 
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#2
kyparamedic said:
I guess this is the place to put this. On most of the systems I've used, you have to wait about .5-1 second after keying up before you begin talking in order to avoid being cut off. At a place I work for currently, there is virtually no lag between the time you keep up and the repeater starts transmitting. It's pretty much instantaneous. However, once you're done talking, the repeater stays on for like 2-3 seconds. Does this have anything to do with it not having any lag time? If not, why does it stay on for so long? This is on a VHF conventional analog system, btw.

Thanks.
The key up lag is usually a function of the PL decoder, and the PL tone being used. Some makes and models of decoders work faster than others. Higher frequency tones can be decoded faster than low frequency tones.

None of this has anything to do with the hang time of the repeater. The purpose of the hang time is so that in a rapid fire conversation, or a signal that has lots of flutter, the repeater transmitter doesn't keep keying on and off. That would add additional squelch tails that the users have to put up with.
 

loumaag

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#3
Another point to consider is if your previous experience is with trunked systems there is a whole process that takes place when you key your radio. That process takes time to happen and accounts for a delay that is inevitable with all trunked systems.
 
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#4
Ok. The PL tones are 118, 141, 192, and 210. All the channels on the system are like this. I've heard quite a few systems and never heard such a long hang time. Just thought it was interesting, and can be a little annoying at times.
 
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#5
loumaag said:
Another point to consider is if your previous experience is with trunked systems there is a whole process that takes place when you key your radio. That process takes time to happen and accounts for a delay that is inevitable with all trunked systems.
I've only used one trunked system, it's an EDACS system. There's no delay on it, but I take it that's because from the time you press the PTT button until you get the "go ahead tone" the repeater has already keyed up? On this note, if there are multiple radios on, sometimes one of them may be a little late picking it up compared to the others, like it was on scan or something but wasn't. Why is this? I used to think they were talking before the beep until I heard it fine on another radio nearby.

Thanks.
 
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#6
If there are multiple receiver sites, there is the additional lag of the comparator process choosing a receiver and applying the audio and the COR signal to the controller. Each step in the process has a time factor, and while each is very short, they add, and with multiple steps, the delay gets longer. That being said, the efficiency of the process is where the delay lies, and that depends upon matching compatibility of components, system setup, and maintenance practices, etc. What you described in your last post suggests a problem with the radio that's not responding as soon. Sometimes it's as simple as some of the programming and/or settings in the individual radio.
 
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#7
On the conventional system, there is only receiver site, so maybe that's why it doesn't take as long.

On the trunked system, I normally notice it on the base radios for some reason.
 

n5usr

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#8
kyparamedic said:
I've heard quite a few systems and never heard such a long hang time. Just thought it was interesting, and can be a little annoying at times.
Why do you find the hang time annoying? Just curious... My repeater actually has a 5 second hang time, specifically to keep the transmitter on when people are having a somewhat-slow conversation. Any shorter, and it tends to drop in between people talking. That is what annoys me! :)

In some particularly old repeater systems, I have seen a delay on keying up if they used tube finals that needed to "warm up" before putting out proper power or frequency, and I've seen some controllers that were just slow - usually as mentioned previously because of slow tone decoders or encoders. Old tone decoders and encoders actually used a vibrating reed, and that took time to get moving.

The most annoying system I've seen is at the newspaper printing plant I occasionally do HVAC work for - for some reason, they must wait for their repeater to drop before the next person talks, otherwise that next person gets cut off. Personally, I'd be all about fixing that if it were my system...!
 
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#9
To keep it simple, whenever you are talking on a repeater, it is best to press the transmit button and pause about a second before talking, to allow for distance from the repeater. if you are 30 miles away, your signal won't sync up on the repeater as compared to someone right under it. Yes there is a need for the PL to decode before you can be heard and understood by others, and there is usually a squelch tail after you quit transmitting, usually a few seconds. Amateur Radio repeaters generally have up to a 5 second tail. I always have said the longest possible tail, as it saves on wear and tear of the controller, be it a relay or actual diode switches.
 
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#10
N1BHH said:
if you are 30 miles away, your signal won't sync up on the repeater as compared to someone right under it.
Huh? at 186,000 miles/second, I don't think distance has much to do with it. And if the receiver is in saturation and is quieting, it doesn't matter what the signal strength is.
 
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#11
zz0468 said:
Huh? at 186,000 miles/second, I don't think distance has much to do with it. And if the receiver is in saturation and is quieting, it doesn't matter what the signal strength is.
You have to consider obstructions, buildings, hills, smog, doppler effect, etc. Light may travel at 186,000 miles per hour in free space, but radio waves don't travel in a straight line in the real world, unless you live in a vacuum. The human body is an attenuator, just like everything around you. Bed sheets attenuate, walls, you name it, there are all kinds of things around you that cause radio waves to refract and reflect.

Here is some interesting reading: http://ecjones.org/propag.html
 

ScanDaBands

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#12
While we are on repeaters , I have one for the gurus.......any idea why a UHF system (TK-850 repeater) using a voter system would "rely" on one voter in particular instead of selecting the "proper" voter ? Dispatch is done through a 911 Com center through software.
 

loumaag

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#13
kyparamedic said:
I've only used one trunked system, it's an EDACS system. There's no delay on it, but I take it that's because from the time you press the PTT button until you get the "go ahead tone" the repeater has already keyed up? On this note, if there are multiple radios on, sometimes one of them may be a little late picking it up compared to the others, like it was on scan or something but wasn't. Why is this? I used to think they were talking before the beep until I heard it fine on another radio nearby.

Thanks.
I am sorry, I guess I misunderstood your OP. The delay between you hitting the PTT and the "go ahead tone" is what I was referring to. The way all trunking systems work, when your radio sounds the okay to talk noise, everything is already lined up including the repeater.

As for a delay on a conventional system because of PL or DPL, that sounds more like a PL/DPL decoder issue on the repeater receiver, unless you have a voter delay. I guess different folks have different experiences, but I will say that I have never noticed any appreciable difference on any PL/DPL vs CSQ situation.

As for distance being a factor, if you can notice the difference between 1 mile and 30 miles even considering terrain obsticales, I am willing to be that you would not be wasting your time on this board (since the difference is 0.000150 +/- seconds). :D
 
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#14
N1BHH said:
You have to consider obstructions, buildings, hills, smog, doppler effect, etc. Light may travel at 186,000 miles per hour in free space, but radio waves don't travel in a straight line in the real world, unless you live in a vacuum. The human body is an attenuator, just like everything around you. Bed sheets attenuate, walls, you name it, there are all kinds of things around you that cause radio waves to refract and reflect.

Here is some interesting reading: http://ecjones.org/propag.html

Just curious how that link supports the idea that it would take a "measurable" difference in time for sound waves to travel 1 mile vs. 30 miles? Dxing is done across countries, and even with all that jargon listed in that link, i still don't think you are going to hear someone talking minutes after he cut off his transmission. Even when i've picked up "skip" on lowband frequencies, the time stamp the dispatcher says is right on with the time i have (given the variance of daylight savings time). And those "skip" transmissions were over 1500 miles from where i was at the time.
I understand the idea of "attenuation" but i don't see how that slows down sound waves. I'd say it weakens the signal before i would say it slows it down, either way i don't see it as being noticeable.

The issues described by the OP sound like electronic issues with the repeater, some of them programmable and some of them not. There is a system in the town next to mine that has the same issue. The repeater will stay keyed up a few seconds after the transmission is cutoff, i just shutoff the delay feature on my scanner because that feature is essentially built into the repeater itself. With the technology of radio systems now, your system may be verifying that your radio is 'suppose' to be on the system to begin with before it will let you talk. Just another step which delays you actually getting out on the radio.
 
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#15
I'm not talking minutes, I am talking milliseconds. Everything in our environment effects how signals go from one place to another and therefor you must compensate for delays. There are electronic issue with the atmosphere. Nothing is perfect, you need to make adjustments for imperfections. If you start talking before you push the transmit button, someone will miss what you say, right? So if there is even a lag in the repeater hearing your signal and the PL it will obviously not retransmit your signal immediately, there will be a lag of, for example 100 milliseconds due to refraction, absorption, etc. The lag varies.

On HF we can sometimes hear what is known as a long delayed echo, which is our signal bouncing back at us or in some cases, actually travelling around the world and back to us.

Propagation is affected by everything even at the short wavelengths that our fire and police agencies, taxi's and all other spectrum users. Many repeaters are set up with a digital delay to compensate for operators being too quick to transmit. There are many reasons for a signal having a lag. Some are and some are not detectable with the ear.
 

kb2vxa

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#16
OK guys let's settle down. It takes time for the tubes to warm up? Last I looked the whole system was on hot standby. This is the sort of misinformation that abounds when non technical people attempt a technical discussion.

To cut to the bone here, transmission delays vary according to the amount of switching and processing between receiver(s) and transmitter. That was simple enough, never mind the cave man over there scowling at his monitor.

"Hang time" as you're calling it is the repeater tail that saves wear and tear on the nerves AND needless processing delays. All that keying up during a conversation is annoying and gets worse with continuous traffic, plus the fact the beginning of a transmission may be lost in a system with multiple site switching and heavy processing. That's one reason the man said it's wise to press the button and wait a second before speaking even on a conventional system, it avoids needless repeats. Then I've seen people start talking before they even press the button, now that really takes the cake.

One last thought on misinformation;
"Many repeaters are set up with a digital delay to compensate for operators being too quick to transmit."

My friend, digital audio processing delay usually about a quarter second kills those annoying squelch tails. There is no way to foolproof a system to compensate for users who don't know how to use a radio due to inadequate training. As a matter of fact the delay is transparent to the user unless somebody has a portable nearby with the volume cranked up, then you hear a mean reverberating echo and in a worst case scenario, feedback like a flying saucer taking off.
 
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#17
Some repeaters utilize a delay controller; it actually causes the repeated audio to be a few milliseconds behind the real time "input" audio, and because of this, you don't need to wait when you key up, the repeater, because of the repeated delay, gets even the first snippet of when you first start talking.

This is seldom used in Public Safety environments or the like. It can start to cause a horrendous echo with even the slightest notion of a radio on frequency in the background. They're more commonly in service on the ham bands.


Astro25
 
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#18
N1BHH said:
You have to consider obstructions, buildings, hills, smog, doppler effect, etc. Light may travel at 186,000 miles per hour in free space, but radio waves don't travel in a straight line in the real world, unless you live in a vacuum. The human body is an attenuator, just like everything around you. Bed sheets attenuate, walls, you name it, there are all kinds of things around you that cause radio waves to refract and reflect.

Here is some interesting reading: http://ecjones.org/propag.html
Heh... ok. All those things can have an impact, and some actually do slow down a radio wave. But seriously... we're talking micro or nano seconds of delay here. Not enough that anyone would actually notice.

The link was interesting, btw, but totally useless in the context of this discussion.
 

n5usr

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#19
kb2vxa said:
OK guys let's settle down. It takes time for the tubes to warm up? Last I looked the whole system was on hot standby. This is the sort of misinformation that abounds when non technical people attempt a technical discussion.
Ah, I knew I should have gone back and reworded that. I had a feeling someone might make a comment about it. It was you - and you threw in a dig on others' technical knowledge - big surprise...

Yes, the tubes themselves are constantly hot. I shouldn't have used "warm up" - bad descriptor. That was the easy, quickie description that was often given (not by me) to those who didn't understand the intricate details of the hardware. But I have seen several tube systems in the past that took some varying amount of time (fractions of a second, to a second or two) to stabilize when switching on the transmitter. There are a number of reasons that would happen, the results are the same - quick-keying users chop the first few words off their transmissions.

This is usually just because the gear is OLD and perhaps in need of service, not inherently because it's tube operated.

All the systems I know the details of have gotten rid of the tubes now. The gear was more trouble than it was worth for remote sites with limited access.
 
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#20
N1BHH said:
I'm not talking minutes, I am talking milliseconds. Everything in our environment effects how signals go from one place to another and therefor you must compensate for delays. There are electronic issue with the atmosphere. Nothing is perfect, you need to make adjustments for imperfections. If you start talking before you push the transmit button, someone will miss what you say, right? So if there is even a lag in the repeater hearing your signal and the PL it will obviously not retransmit your signal immediately, there will be a lag of, for example 100 milliseconds due to refraction, absorption, etc. The lag varies.

On HF we can sometimes hear what is known as a long delayed echo, which is our signal bouncing back at us or in some cases, actually travelling around the world and back to us.

Propagation is affected by everything even at the short wavelengths that our fire and police agencies, taxi's and all other spectrum users. Many repeaters are set up with a digital delay to compensate for operators being too quick to transmit. There are many reasons for a signal having a lag. Some are and some are not detectable with the ear.
Good Morning Clyde, All,

Clyde, What you eluded to is called "backscatter". When those of you have the proper ham ticket, you can check into the "BackScatter Net on 28.825 and when conditions are right, hear, with delay some "fluttering" transmissions. These usually are stations that are just out of the reach of "groundwave", but too near for "skip" conditions. I've worked stations on 28.825 that way, San Antonio, Paris, Tx, Little Rock, AR, even down near Baton Rouge, LA. Those signals are going all the way @round the World and coming back. Reception of these "backscatter signals" is the same way. MOST of the time, if you point your beam antenna in the opposite path direction (not always the compass direction) you'll be able to hear these stations better

Respectfully,
73,

Don/KA5-LQJ
Ten-Ten International
No Bull **** Radio Club (NBSRC) - Chapter 2
Red River Valley Amateur Radio Society
Certified NOAA Storm Spotter
 
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