Thorny41587
Member
This seems like the post for it, do the new digital, or any public safety radio for that matter, have a squelch tail on it? Can the programmer control that? And if so, do the radios have them or... thanks.
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N_Jay
Guest
Thorny41587 said:
Squelch Tail is an artifact of the way analog squelch citcuits work.
In general Didital radios will mute without any noticable noise.
Under certain cercunstances you can get some noise, such as if a signal fades out an dteh last paket is atempted to be decoded bu is not decoded successfully.
Thorny41587
Member
Is that why on analog trunking system you don't hear squelch? It just fades away... or is this in correct?
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N_Jay
Guest
Thorny41587 said:
As long as the radio receives the code that tells it to mute, you will not hear any noise.
This really applies to analog radios only, but it's referred to as squelch tail eliminator (STE) by some of the manufacturers and consists of a burst of the CTCSS subtone at the end of transmission encoded so as to allow the receiving radio decode it as a cue to turn off the receiver audio. As long as the receiver audio turns off before the carrier drops, you hear......nothing. It can also be done by simply turning off the transmitter subtone about a half second before the carrier drops. The receiving radio will simply turn off the audio because the CTCSS subtone is no longer there. There are repeater systems that turn off the repeater transmit subtone as soon as the carrier coming into the receiver from a mobile or control station drops. That way, the repeater hang time is still there, but there's no CTCSS subtone being transmitted, so the receiving mobiles and control stations turn off the receiver audio and go silent. When this is done, even radios without STE will go silent with no squelch tail just because the subtone is no longer there to keep the audio open.
Digital systems can't decode noise, so they simply turn off the audio when there's no longer any digital intelligence being received.
Digital systems can't decode noise, so they simply turn off the audio when there's no longer any digital intelligence being received.
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N_Jay
Guest
wx4cbh said:
Thats one way, it was often called "PL Reverse Burst", in DPL there is a turn-off code which is simply 101010101 . . . 010101
Trunking has low speed data with a mute code. Digital has Null packets.
Yep, and sorry I didn't post about the DPL side. As for the analog PL style, some radios simply look for the change in the PL tone, while others look specifically for the encoded wave properties of the shut-off burst. There's another twist in the saga and it's called non-standard squelch tail eliminator. Motorolas, if programmed for non-standard, then look for a change and react to that as do the other radios that don't look for the encoded wave properties.
This discussion could go on all night about the whys and wherefores of simply killing the squelch tail. It's never as simple as it sounds. STE is used for more than just turning off the audio in some systems.
This discussion could go on all night about the whys and wherefores of simply killing the squelch tail. It's never as simple as it sounds. STE is used for more than just turning off the audio in some systems.
Just prior to the end of the transmission the disconnect word is sent, which is what N_Jay referred to by low-speed data. If message trunking is used there tends to be a delay in sending whereas with transmission trunking at the end of unkey the word is sent and the carrier drops instantly.Thorny41587 said:
If you listen closely with headphones you'll hear a hum at the end of the transmission. That the disconnect tone/word.
-Wayne
Thorny41587
Member
I have heard that on our trunking system. (Toledo's System), is it about a 1 second hum, when the repeater drops? That somewhat sounds like ECADS? Is this what you're refereing to? Also, is there anyway to control how long the hang time repeater is set for? EX: (Toledo’s Type II Systems hang time was about 5 seconds, now it’s about 2
Hang time on older repeaters is set by an adjustment on the repeater control panel, and is set in the software of newer equipment. On most analog repeaters, the hang time begins with the drop of the carrier coming into the receiver. In more complicated systems, the STE is used to initiate end-of-transmission protocols vs loss-of-signal protocols that are part of the operating system. Those protocols involve hang time but hang times aren't necessarily the only things involved. That's why just shutting off the tone isn't sufficient for more complicated systems, though they deal with it without much trouble, and determining which protocol(s) to initiate is even more important with trunking systems.
MCX and Micor squelch
The design of the squelch circuits in the Micor and MCX90/100 series allow for a very quiet unkey, even in carrier squelch. They have 2 squelch modes, fast and slow. When the signal is strong, the radio uses fast squelch which mutes the radio with no noise at all. When the signal is weaker there might be some noise, like most other radios. With my MCX90's there is no difference in the way the radio mutes no matter if it is a PL or carrier squelch channel.
It all depends on the designof the radio, and if the radio responds to reverse burst or not.
I notice that all truning systems mute really nicely on my PRO95.
Josh
The design of the squelch circuits in the Micor and MCX90/100 series allow for a very quiet unkey, even in carrier squelch. They have 2 squelch modes, fast and slow. When the signal is strong, the radio uses fast squelch which mutes the radio with no noise at all. When the signal is weaker there might be some noise, like most other radios. With my MCX90's there is no difference in the way the radio mutes no matter if it is a PL or carrier squelch channel.
It all depends on the designof the radio, and if the radio responds to reverse burst or not.
I notice that all truning systems mute really nicely on my PRO95.
Josh
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