Squelch Tail Question

[fmalloy]

The squelch tail is caused by your radio. The squelch circuit has to see the noise after the carrier drops before it will mute the audio.

I don't understand why this is true - can't it mute right when the carrier drops?

With electronic circuits being very, very fast, I don't understand why the audio can't be muted so fast that any tail wouldn't be noticeable.

Definitely not trying to question you, just want to understand this better - my wife is a lot more tolerant of the Moto trunked systems with the very clean transmission ends. If I could eliminate the tail on the conventional channels I'd be able to do a lot more listening

 

[nd5y]

I don't understand why this is true - can't it mute right when the carrier drops?

With electronic circuits being very, very fast, I don't understand why the audio can't be muted so fast that any tail wouldn't be noticeable.

Motorola solved that problem a long time ago. Micor Squelch I never understood why nobody else does it.

 

[rfradioconsult]

Motorola had reverst burst on the Motrac, the Micor implemented a two-stage carrier squelch that provided for a faster squelch closure on strong signals, weaker signals still had to usual "slow"closure.

 

[jackj]

The way things work.

I don't understand why this is true - can't it mute right when the carrier drops?

With electronic circuits being very, very fast, I don't understand why the audio can't be muted so fast that any tail wouldn't be noticeable.

Definitely not trying to question you, just want to understand this better - my wife is a lot more tolerant of the Moto trunked systems with the very clean transmission ends. If I could eliminate the tail on the conventional channels I'd be able to do a lot more listening

A squelch circuit is just a circuit that mutes the audio when no signal is present. FM radios generally have a lot of gain in their Intermediate Frequency (IF) stages. They generate a lot of noise that is masked by the received signal but when there is no signal the noise shows up as a high pitched hissing or rushing.

The squelch circuit samples the audio through a high-pass filter with a cutoff frequency of around 3 KHz. It amplifies this high pitched noise and then rectifies it to produce a varying DC voltage that is proportional to the amount of noise. This DC voltage is then applied to a mute switch to mute the audio when the noise increases to a certain level.

To keep the squelch from rapidly opening and closing on signals that are close to the noise threshold they have a certain amount of hysteresis or time delay built in to them. This hysteresis is one of the main reasons why there is a squelch tail when the carrier drops.

All of this applies only to analog, carrier-squelch radio receivers. A receiver that can be set to open the audio only when it receives the proper sub-audible (PL) tone or digital squelch code won't have a squelch tail when receiving a Motorola system. Motorola transmits an inverted the tone signal for a few milliseconds and then drops the PL tone or send a code to close the digital squelch before they drop the carrier. Digital radio receivers receive a data stream and apply that to a digital-to-analog converter. The receiver's audio is generated by this converter and the converter will have no output with no data input so it doesn't need a squelch circuit.

This is a very basic description of how a squelch circuit works. I hope it helps you understand why you hear a squelch tail on some systems.

 

[chrismol1]

Lots of radio have an LED on the top of them, will light up when theres an incoming transmission or transmitting.
Squelch tails are cool if you want to play the "radio game" .... my..2 cents..

Personally i kinda like the ability to hear the squelch taill, reason is when one is in a noisy area (like when i`m outside and it`s noisy from city and traffic noises) i know when a transmission ends. Same for when i`m using my ham HT, i like to hear the taills so i know if i`m reaching the repeater, or when on a simplex channel, i can hear when the person i`m in contact with has ended his/her transmission. So, somethines it`s a good thingy to be able to hear the squelch taills . Another good thing about that is i don`t need to look at the display too much when i`m using ether the scanner or the ham HT, as the squelch taill gives m an indication of what channel/repeater i`m listening to or (in the case of my ham radio) talking on, i just memorize the way the repeaters sound (including the squelch taill and any marker or "courtesy tone" that is included), that way i know which repeater or channel i`m hearing. N9NRA

 

[picaflor]

How to kill squelch tails on a Uniden...

This only works with trunking Motorola systems though, but it works like a charm.

If what you're listening to is a Motorola trunking system, in the system options menu set the end code option to analog+digital.

I use a 396xt to listen to the sf public safety system, enabling end code detection makes a world of difference.

Not sure about conventional systems though...

 

[N9NRA]

squelch tail muting.

Lots of radio have an LED on the top of them, will light up when theres an incoming transmission or transmitting.
Squelch tails are cool if you want to play the "radio game" .... my..2 cents..

Hey there, yeah, i know, as my HT has one, so i can agree with ya . However when we have skywarn nets around here they use the tail to put out weather-related messages and such, can`t hear those if ya mute the squelch tail, but i do get what ya mean. Thanx. 73. N9NRA

 

[parnass]

..
There is no way you can completely eliminate the squelch tail on carrier squelch radios. There will always be a small amount of time required for the squelch circuit to sense the noise and mute the audio. You'll just have to live with it.

It is possible to shorten the squelch tail on some older radios, e.g., Radio Shack PRO-51, but I don't have any information about the circuitry used in the current Uniden models.

Link: http://wcilscanner.home.comcast.net/~wcilscanner/mods/pro51.txt

 

[W6KRU]

It is possible to shorten the squelch tail on some older radios, e.g., Radio Shack PRO-51, but I don't have any information about the circuitry used in the current Uniden models.

Link: http://wcilscanner.home.comcast.net/~wcilscanner/mods/pro51.txt

My PSR-500 has the adjustment. I set it to a minimal value and hear no squelch tail.