What determines repeater pre-time?
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hooknladder
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What determines repeater pre-time?
Wondering what determines the time between when you key your radio up and the start of the repeater transmitting your message. Our local fire repeater comes up at the click of the ptt switch. The med repeater is a different story. A minimum of 700ms is needed for the pre-ptt tone before the repeater comes up.
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Jim2121
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pre-time
most likely in the operators manual. Here's one we use without a control Head
http://www.nycomco.com/TKR820.htm
Some we use with a Controller, another ex:
http://www.catauto.com/cat300.html
Since I have the week off, I don't have access to any models of repeaters, nor did you list one... Do you have someone who services these units? run it bye past him what you are looking to do.
I need to be at the repeater to fully answer your question.....
anyone else?
http://www.nycomco.com/TKR820.htm
Some we use with a Controller, another ex:
http://www.catauto.com/cat300.html
Since I have the week off, I don't have access to any models of repeaters, nor did you list one... Do you have someone who services these units? run it bye past him what you are looking to do.
I need to be at the repeater to fully answer your question.....
anyone else?
I believe the concept you are asking about is called "attack time," i.e., how long before an incoming signal hits the receivers' antenna before the audio is being transmitted over the transmitter?
Attack times will vary widely depending on repeater configuration; it is a function of the number of steps that have to be accomplished before the audio path is open. Consider, for instance, a simple in cabinet repeater with an idling exciter; before audio passes, the following steps have to happen:
Receiver detects valid freq. (about 20-40 ms);
Receiver detects valid tone (about 150-200 ms);
Controller sends PTT signal to transmitter (very quick);
Xmit tone encoder powers up and settles on programming freq. (???);
Exciter powers up and settles on freq. (about 10-50 ms);
Amp deck powers up and stabilizes (about 10-50 ms);
Audio passes.
Note that some of the steps (notably the power up steps) can occur simultaneously.
Nonetheless, when departments were first repeaterizing 10-20 years ago, the rule of thumb that was used for training purposes was about 500 ms (half a second) between being hit with signal and passing audio. So we used to train guys to "Press, Pause, Speak."
Life becomes more complicated if MDC is used, if multiple voted receivers are used, sometimes if external controllers are used, and so forth.
Strictly as a guess, I'd venture that your FD repeater is comparatively simple (but still has an attack time of at least 200-250 ms) and your EMS repeater is more complicated.
Attack times will vary widely depending on repeater configuration; it is a function of the number of steps that have to be accomplished before the audio path is open. Consider, for instance, a simple in cabinet repeater with an idling exciter; before audio passes, the following steps have to happen:
Receiver detects valid freq. (about 20-40 ms);
Receiver detects valid tone (about 150-200 ms);
Controller sends PTT signal to transmitter (very quick);
Xmit tone encoder powers up and settles on programming freq. (???);
Exciter powers up and settles on freq. (about 10-50 ms);
Amp deck powers up and stabilizes (about 10-50 ms);
Audio passes.
Note that some of the steps (notably the power up steps) can occur simultaneously.
Nonetheless, when departments were first repeaterizing 10-20 years ago, the rule of thumb that was used for training purposes was about 500 ms (half a second) between being hit with signal and passing audio. So we used to train guys to "Press, Pause, Speak."
Life becomes more complicated if MDC is used, if multiple voted receivers are used, sometimes if external controllers are used, and so forth.
Strictly as a guess, I'd venture that your FD repeater is comparatively simple (but still has an attack time of at least 200-250 ms) and your EMS repeater is more complicated.
Your fd repeater is probably a carrier squelch repeater(very fast on the draw) The other, probably is a tone or dpl machine which takes a little longer to attack the mobiles reciever. Also, there are controllers which have an "anti kerchunker timer" which is designed to keep the causual kerchunker guy from annoying the rest of the bunch...these timers are programmable to the descrecion of the repeater tech and will stop[ the casual idiot from bringing up the repeater,just cause he can.)
mod
mod
An anti-kerchunk feature on a repeater controller should not affect attack time. What this feature does is to suppress the repeater tail after the input freq drops if the input duration was less than the setpoint of the feature; what it does is to prevent a user from keying the machine briefly and then hearing the tail he himself generated.
The anti-kerchunk feature is there to prevent quick, usually unidentified, incoming transmissions from actually causing the repeater to key up. On many controllers, this is only enabled if the repeater's transmitter is off. Once the transmitter is already on, this time delay is usually disabled.
There is such a pre-repeat delay on the MSF5000. One of its uses would be to suppress repeating of any MDC identification that occurs when a user first keys up. I can't think of any other reason a repeater would want to delay the initial key-up.
If any system still exists that is lucky enough to have a carrier-only squelch repeater, I'd be very surprised. The radio waves are so crowded, that PL or DPL is almost a guaranteed requirement on any repeater. Usually they're located on good high locations and are subject to hearing a lot more than they need to.
There is such a pre-repeat delay on the MSF5000. One of its uses would be to suppress repeating of any MDC identification that occurs when a user first keys up. I can't think of any other reason a repeater would want to delay the initial key-up.
If any system still exists that is lucky enough to have a carrier-only squelch repeater, I'd be very surprised. The radio waves are so crowded, that PL or DPL is almost a guaranteed requirement on any repeater. Usually they're located on good high locations and are subject to hearing a lot more than they need to.
Well, that may be _their_ definition of it, but the whole idea of anti-kerchunking is to eliminate the keyup of the repeater entirely with just a quick transmission from another user. The fact that the repeater keys up immediately but then doesn't stay on very long still results in some action from the kerchunking transmission. All that does is make the person keep keying up until he/she does hear a tail from the repeater. To discourage that, the repeater should not key up at all until a valid (i.e. sufficiently long) transmission occurs when the repeater is not transmitting. Just making the hang time zero does nothing to prevent the repeater from keying up for that split second when there's a short-duration input signal.
Some repeaters even attempt to detect audio to enable the transmitter, so even a long silent carrier won't key it up; you must say something or make some kind of noise along with the carrier. The best, and legal, thing to do, is to identify your keyup with a callsign.
A properly designed anti-kerchunk circuit, or software, should only have an effect if the transmitter if it's already off. Once it's on, it should have no effect at all and any keyup should result in an instant, undelayed repeat operation.
If you consider this to be an initial pre-keyup delay, and that's what it really does when you examine it, then that would also prevent or minimize kerchunking.
Bob M.
Some repeaters even attempt to detect audio to enable the transmitter, so even a long silent carrier won't key it up; you must say something or make some kind of noise along with the carrier. The best, and legal, thing to do, is to identify your keyup with a callsign.
A properly designed anti-kerchunk circuit, or software, should only have an effect if the transmitter if it's already off. Once it's on, it should have no effect at all and any keyup should result in an instant, undelayed repeat operation.
If you consider this to be an initial pre-keyup delay, and that's what it really does when you examine it, then that would also prevent or minimize kerchunking.
Bob M.
For commercial use the proper way to handle kerchunking is the CSI TP-154’s method as RKG mentioned. Having to hold the PTT button for any length of time before speaking is not acceptable for commercial use and would generate all kinds of complains.
For ham use, where the transmitter does not key up at all until some time has passed from an idle key up is acceptable and perhaps desirable if someone is constantly monitoring a quiet repeater, but not very nice for strangers that like to know if there is actually a repeater on the frequency and if they are in range.
In the end, it is pointless since a kerchunker will soon realize how to defeat the system.
Nand.
For ham use, where the transmitter does not key up at all until some time has passed from an idle key up is acceptable and perhaps desirable if someone is constantly monitoring a quiet repeater, but not very nice for strangers that like to know if there is actually a repeater on the frequency and if they are in range.
In the end, it is pointless since a kerchunker will soon realize how to defeat the system.
Nand.
In RKG’s example he mentions that the exciter is idling. This means that the transmitter can be extremely fast in coming on line. Repeaters built with mobile radios and particular synthesized radios can be a lot slower since the TX radio needs to switch from RX to TX and setup the TX synthesizer as well before the PA can be anabled.RKG wrote: ….. Consider, for instance, a simple in cabinet repeater with an idling exciter…..
This is one more good reason to use a real repeater instead of mobiles.
Nand.
Not that I would know by experienceNand wrote: In the end, it is pointless since a kerchunker will soon realize how to defeat the system.
but that is exactly right. If you need to hold the PTT for 1 second to get a repeater trail, that is what they will do. It will go like this:Short click - "No repeater trail. WTF"
Another short click - "Still no repeater trail. Damn it."
Hold the PTT for a few seconds out of frustration - "Bingo! Repeater trail."
Most don't give up on the first click.
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Them: "A very nice CB at 900Mhz speed!"
On that note, perhaps the best way to eliminate "kerchunking" is to set the repeater's hang time to zero. If the ever so brief tail is even heard the errant "kerchunker" will often confuse it with the usual small noise a "subscriber" radio has going from t/r. They soon learn to actually call another user to check their radio's performance.
Zero-length tails have been tried as anti-clicker strategies, but generally have been found to be unsatisfactory.
One of the purposes of a tail is to permit responses to commence with effectively zero attack time -- since the repeater is still transmitting. This is particularly useful, since people responding to a call are even more prone than people initiating a call to begin speaking too quickly and therefore to clip themselves if the machine has to go through the whole key-up sequence for each segment of the conversation.
There is also a view that another function of tails is to lengthen the life of a repeater by reducing the number of key-up sequences, which, according to this theory, are disproportionately hard on the hardware. I don't know if this view has an validity.
One of the purposes of a tail is to permit responses to commence with effectively zero attack time -- since the repeater is still transmitting. This is particularly useful, since people responding to a call are even more prone than people initiating a call to begin speaking too quickly and therefore to clip themselves if the machine has to go through the whole key-up sequence for each segment of the conversation.
There is also a view that another function of tails is to lengthen the life of a repeater by reducing the number of key-up sequences, which, according to this theory, are disproportionately hard on the hardware. I don't know if this view has an validity.
"There is also a view that another function of tails is to lengthen the life of a repeater by reducing the number of key-up sequences, which, according to this theory, are disproportionately hard on the hardware. I don't know if this view has an validity."
Back in the good old days when people used vacuum tubes in the transmitters, 600 volt power supplies, relays to switch the supplies on and off, and antenna relays for RF, yes, all these short key-ups were hard on the equipment. These days, there are usually no more tubes, or high voltage supplies, or relays of any kind, so the short key-ups probably don't hurt things at all.
As a repeater trustee, the most annoying thing about kerchunkers is the fact that they don't identify their transmissions. They sometimes just sit there, keying things up every 10 seconds, trying to find a good spot (they think) to hit the repeater. Every time they key up and the repeater responds, they're in a good enough spot. If they just gave a callsign and spoke their intent to talk to someone or test, then life would go on joyously. I've gotten good at recognizing background sounds when people just key up for a couple of seconds, then go somewhere else.
I think there's at least one person in CT who thinks it's his/her job to go around every morning (like clockwork) keying up every repeater in the state, channel-by-channel, just to see what's still working. My cat does this kind of exercise every day - go outside to see if it's still there, then come inside because something might have changed (yeah, like I'm going to rearrange the furniture or replace the rugs), then back outside because it's been three minutes since I've checked out that environment, etc... All you cat owners can surely attest to the old in/out/in/out. Something about doors, even glass ones, that fascinates them !
Bob M.
Back in the good old days when people used vacuum tubes in the transmitters, 600 volt power supplies, relays to switch the supplies on and off, and antenna relays for RF, yes, all these short key-ups were hard on the equipment. These days, there are usually no more tubes, or high voltage supplies, or relays of any kind, so the short key-ups probably don't hurt things at all.
As a repeater trustee, the most annoying thing about kerchunkers is the fact that they don't identify their transmissions. They sometimes just sit there, keying things up every 10 seconds, trying to find a good spot (they think) to hit the repeater. Every time they key up and the repeater responds, they're in a good enough spot. If they just gave a callsign and spoke their intent to talk to someone or test, then life would go on joyously. I've gotten good at recognizing background sounds when people just key up for a couple of seconds, then go somewhere else.
I think there's at least one person in CT who thinks it's his/her job to go around every morning (like clockwork) keying up every repeater in the state, channel-by-channel, just to see what's still working. My cat does this kind of exercise every day - go outside to see if it's still there, then come inside because something might have changed (yeah, like I'm going to rearrange the furniture or replace the rugs), then back outside because it's been three minutes since I've checked out that environment, etc... All you cat owners can surely attest to the old in/out/in/out. Something about doors, even glass ones, that fascinates them !
Bob M.
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c17loadsmasher
- Posts: 200
- Joined: Mon Jul 21, 2003 7:26 pm
I haven't seen any hardware related problems that can be attributed to "zero" hang time with any of my repeaters . As stated, this issue is largely dependent on what equipment you employ. On the more modern equipment, an audio delay circuit compensates for the "TX set up" time, and the older stations have minimal TX attack times as they are crystal units, with transistor switching.
What about the repeater kerchunking when a signal is fading in/out (aka picket fencing) and the TX radio of the repeater, having no hang time, clips along with the COR line?
Personally, I think thats alot more annoying than someone just "waking up" the repeater every now and then.
One security contract I worked on (using 1 site UHF repeater) most of the users upon powering up their portable would kerchunk the repeater to confirm that the radio is functional.
Problem now is, they've replaced components of the repeater (tried to find out what was changed and what they are/were using to no avail.) and the repeater has no hangtime so it behaves exactly as described in the first paragraph.
Before the change, the HT1000's would get a squelch tail from the repeater unkeying and that didn't seem to bother anyone but if the new repeater doesn't have reverse-burst, I can just imagine the noise combination of a picket fencing signal triggering the repeaters TX radio and the squelch tail heard on the HT1000s.
Bottom line: No hangtime can be more of a pain in the ass than the casual kerchunker especially if the squelch threshold is set high.
...Just my 1.7456 cents Canadian
Personally, I think thats alot more annoying than someone just "waking up" the repeater every now and then.
One security contract I worked on (using 1 site UHF repeater) most of the users upon powering up their portable would kerchunk the repeater to confirm that the radio is functional.
Problem now is, they've replaced components of the repeater (tried to find out what was changed and what they are/were using to no avail.) and the repeater has no hangtime so it behaves exactly as described in the first paragraph.
Before the change, the HT1000's would get a squelch tail from the repeater unkeying and that didn't seem to bother anyone but if the new repeater doesn't have reverse-burst, I can just imagine the noise combination of a picket fencing signal triggering the repeaters TX radio and the squelch tail heard on the HT1000s.
Bottom line: No hangtime can be more of a pain in the ass than the casual kerchunker especially if the squelch threshold is set high.
...Just my 1.7456 cents Canadian
Orbit 303 wrote- "What about the repeater kerchunking when a signal is fading in/out...SNIP...I think thats alot more annoying than someone just "waking up" the repeater every now and then.
I agree, fortunately, my stations have sufficent elevation AMSL to insure excellent coverage of the intended service area. As I said before, it depends on the kind of equipment in use; some systems won't tolerate zero hang time very well. A bit of squelch hyteresis (sp?) helps the picket fencing on analog channels also.
I agree, fortunately, my stations have sufficent elevation AMSL to insure excellent coverage of the intended service area. As I said before, it depends on the kind of equipment in use; some systems won't tolerate zero hang time very well. A bit of squelch hyteresis (sp?) helps the picket fencing on analog channels also.
Many of the better controllers have a setting designed to deal with this problem: provided that valid freq and tone have been detected for at least a thresthold length of time, the controller will keep the repeater up for X ms in the absence of tone so long as freq is valid. Thus, from CSI:
"CTCSS/DCS hold delay: A software timer that fills in momentary DCS or CTSS loss when a signal is weak. When the hold delay is set to at least two seconds the effective receiver sensitivity is precisely the same as the receivers' squelch sensitivity."
"CTCSS/DCS hold delay: A software timer that fills in momentary DCS or CTSS loss when a signal is weak. When the hold delay is set to at least two seconds the effective receiver sensitivity is precisely the same as the receivers' squelch sensitivity."
If you run PL (DPL), and you expect to decode MDC on the output of the repeater, you'll have to increase the pretime enough that the repeater consistently keys (with all the preliminary activities taking place) and transmits at least a small amount of the dry clocks (the phone ringing type noise you get when you crank up the pretime). 700 MS seems far too long. If you program a radio for no MDC, and key your mike with a cranked carrier squelch portable nearby, how long after you key before you get feedback? If it's a really short time, something might be chewing up the beginning of your message when the receiver in the repeater first opens. Can you disable the PL requirement for testing? Someone else mentioned pre-repeat delay. Maybe it's on, and you're getting around it by really extending the pretime. For that matter, what kind of repeater is it? Another possibility, if it really takes that long to key is to use one of these http://www.nhrc.net/nhrc-dad/ It goes in the audio path after the carrier squelch gate. It actually delays the audio - and yes, MDC will pass uncorrupted thru it - while the PL/DPL stuff figures out if there's a valid tone. Say it takes 500 MS for the PL decoder to validate, and the repeater to start making RF, you would set this for maybe 256 - 512 MS delay. The output audio from this goes towards the transmitter, and you're sending audio starting from 12 MS before the the carrier squelch even opened assuming 512 delay. The repeater tail delay takes care of making sure the transmitter stays keyed for the end of the message after the carrier/PL drops on the input. The delay doesn't get noticed by anyone except maybe the originator of the message who, if you need to use enough delay, may hear the last thing that they said after they unkey.