Does the SQUELCH have any effect when scanning a trunked system? I have no attenuation turned on and rotating the SQUELCH knob seems to do nothing.
Squelch for Trunked System?
- Thread starter WeldGuy
- Start date
- Status
satosi
Member
It does have an effect on the talkgroup frequencies at least, but I'm not sure if it affects the control channel reception.
More time...
I guess I was expecting it to "fry" when turned all the way down, but trunked systems may not work that way. Now that I have had some success receiving traffic on the trunked system, I see SQUELCH does affect actual transmissions.
I'm learning... slowly.
I guess I was expecting it to "fry" when turned all the way down, but trunked systems may not work that way. Now that I have had some success receiving traffic on the trunked system, I see SQUELCH does affect actual transmissions.
I'm learning... slowly.
Squelch setting actually affects all signals. If the signal is not strong enough to "break squelch" the scanner won't "see" the signal. If the squelch is set too low, then it will see every frequency it stops on as having a signal.
This is true for trunked, conventional, analog, and digital. However, for trunked and digital, squelch is not the sole determinant for whether the speaker path opens. For a trunked system, squelch does not open until the scanner sees the control channel issue a channel grant and the scanner goes to the voice channel frequency. For digital, the speaker path does not open until the digital begins to be decoded.
Some ramifications on a trunked system for bad squelch settings are:
This is true for trunked, conventional, analog, and digital. However, for trunked and digital, squelch is not the sole determinant for whether the speaker path opens. For a trunked system, squelch does not open until the scanner sees the control channel issue a channel grant and the scanner goes to the voice channel frequency. For digital, the speaker path does not open until the digital begins to be decoded.
Some ramifications on a trunked system for bad squelch settings are:
- If squelch is set too open, then every frequency will appear to have a signal. This can make it take longer for the scanner to initially acquire the control channel (it will spend extra time on every frequency programmed for the system until it actually sees the data).
- If the scanner misses the end code at the end of a voice transmission, you will hear static (the "fry" noise), as the scanner will not know that the voice comms have ended. Signal dropping below squelch threshold always causes the scanner to return to the control channel, even if End Code has not been detected (it assumes that the end code was missed).
- If squelch is set too tight then the signal might never be acquired or could drop out unexpectedly, even with a relatively strong signal.
troymail
Silent Key
Why should the squelch matter at all if the control channel says there is activity on the talkgroup?
Well, in addition to the examples I gave above, here is another scenario:
It is possible for the voice channel to have a slightly different power distribution than the control channel. In that event, it is possible for the control channel to be strong enough to receive at a high squelch setting, but when the channel grant directs the scanner to go to the voice channel frequency, the signal there is not strong enough to break squelch. What you would see is the scanner jump to the voice channel frequency, then immediately return to the control channel.
From the scanner's point of view, either it decoded the channel grant incorrectly or it calculated the wrong voice frequency (i.e. the band plan is entered incorrectly).
Remember, the only way a scanner knows that a signal is present is for the signal to be strong enough to be over the squelch threshold. Even if the control channel tells the scanner that a signal is present on a frequency, if the signal doesn't break squelch, the scanner won't see it.
It is possible for the voice channel to have a slightly different power distribution than the control channel. In that event, it is possible for the control channel to be strong enough to receive at a high squelch setting, but when the channel grant directs the scanner to go to the voice channel frequency, the signal there is not strong enough to break squelch. What you would see is the scanner jump to the voice channel frequency, then immediately return to the control channel.
From the scanner's point of view, either it decoded the channel grant incorrectly or it calculated the wrong voice frequency (i.e. the band plan is entered incorrectly).
Remember, the only way a scanner knows that a signal is present is for the signal to be strong enough to be over the squelch threshold. Even if the control channel tells the scanner that a signal is present on a frequency, if the signal doesn't break squelch, the scanner won't see it.
troymail
Silent Key
Ok - I guess the thing is that the scanner doesn't monitor the control channel stream once the voice channel is tuned in and therefore the radio relies on the strength of the voice channel to hold the lock.
Do true subscriber radios (Motorola, etc.) work this way too?
Do true subscriber radios (Motorola, etc.) work this way too?
Not sure, but I think they would have to. If a trunked radio does not see any signal on the voice channel frequency, it should return to the control channel, even if it hasn't seen an End Code. Otherwise, it could just hang for a while and be missing channel grants. AFAIK, even subscriber units only have a single receiver, so when they are on a Voice Channel, they, too, are not monitoring the control channel.
troymail
Silent Key
So what we really need is to
(a) have only the control channel frequencies programmed,
(b) have the radio/scanner find the control channel and remember it,
(c) have the radio quickly leave the control channel and search a new one once the proper signature isn't found and find the new one, and
(d) keep the squelch wide open
(a) have only the control channel frequencies programmed,
(b) have the radio/scanner find the control channel and remember it,
(c) have the radio quickly leave the control channel and search a new one once the proper signature isn't found and find the new one, and
(d) keep the squelch wide open
(d) would be a bad idea. If the squelch is wide open, then the scanner is going to take an additional .5 seconds or so on every frequency trying to determine whether it is carrying control channel data. And, as mentioned above, if the End Code is missed on a Voice Channel when a comm ends, then the scanner is going to hang on the voice channel and you'll hear "fry" noise or the comms from the next group to use the channel.
change (d) to: have the squelch set to a reasonable level
change (d) to: have the squelch set to a reasonable level
Boatanchor
Member
- Joined
- Jul 17, 2011
- Messages
- 991
UPMan commenting on the GRE thread lol
Last edited:
You'd be surprised who all asks me for help.... and I'm happy to give it.
And his information is quite correct too from my experience with GREs.
"Upman" is the BEST, he helped us perfect the "Motorola Shuffle System " for our scanners here in ILL for both Uniden and GRE scanners.....We would have been sunk with out his knowledge.....
RKG
Member
Essentially, yes.
When a subscriber selected on a talkgroup sees (over the control channel) an OSW signifying a voice channel grant in response to some other subscriber's ISW, the subscriber radio switches to the assigned voice channel and waits a given period for something to happen. In general, that something involves waiting to hear the low-level handshake between the assigned voice channel and the initiating subscriber.
At that point, the listening subscriber holds on the voice channel until something happens. What the "something" is depends on the trunking format for which the system is programmed. If the format is "message trunking," the listener holds on the voice channel until the connect tone drops and a hang timer elapses. If the format is "Transmission trunking," the listening suscriber reverts to the control channel as soon as the disconnect tone is heard from the initiating subscriber. (Any further transmissions of the same exchange require a new voice channel assignment.)
GRE 500 Garbled sometimes
I am new to the P25 system. I have it set up with all of the control channels and TG's. Sometimes the conversations start out very clear then go to digital garble. Is this a system trait or something I possibly have set wrong in the scanner. Thanks for you help
I am new to the P25 system. I have it set up with all of the control channels and TG's. Sometimes the conversations start out very clear then go to digital garble. Is this a system trait or something I possibly have set wrong in the scanner. Thanks for you help
Ideally you'd have the ability to program squelch per channel. IE, the control channel frequencies would be squelched but the voice channels wouldn't be. Motorola radios work like this - the voice channels aren't squelched. This means even if the signal goes in the crapper, you'll still here something. The control channel isn't squelched either, the radio searches the programmed channels until it finds something it likes (IE, the system ID).
If it actually worked that way, then in weak-signal areas you'd be constantly hanging on open squelch noise.
reconrider8
Member
i either run my sq at like 12oclock for jsut scanning around "normal" or at liek 630-8oclock when im searching for new stuff ie new systems ect
- Status
