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Desktrac squelch tail

This forum is for discussions regarding System Infrastructure and Related Equipment. This includes but is not limited to repeaters, base stations, consoles, voters, Voice over IP, system design and implementation, and other related topics.

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n9upc
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Desktrac squelch tail

Postby n9upc » Thu Aug 07, 2003 4:13 pm

Greetings,

I have a customer who just made the jump from simplex to a Desktrac repeater. They bought the repeater used and found out some very uneasy things today.

1.) The repeater will not do split tone capability. AKA different PL/DPL for TX and RX.

and

2.) The sql tail is transmitted with the PL so you hear the radio unkey and then you hear the repeater unkey.

The split tone thing was not an issue and was over come with great ease, but the sq. tail thing is starting to slowly become an issue.

So does anyone know how to eliminate the PL from being transmitted with a sql. tail????? Or if that can not be done then at least shorten the sql tail greatly!!!!

Any and all help would be great.
" ah the fatman made a funny!" - Stewie from the family guy.

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Pj
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What radios do you own?: X9000 thru APX

Postby Pj » Thu Aug 07, 2003 4:36 pm

May have checked already...but have you checked for the reverse burst option?
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Susan157
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Joined: Fri Apr 19, 2002 5:15 pm

You can do it

Postby Susan157 » Thu Aug 07, 2003 4:54 pm

:wink:

the desktracs we have worked on are only
maxtrac radios and you can do what you like
with the pl/dpl/cs

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xmo
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Postby xmo » Thu Aug 07, 2003 7:12 pm

Susan157 is correct - you can put whatever PL/DPL you want into the transmit and receive radios independently - but - you need to use Maxtrac RSS to talk to them. The Desktrac RSS tries to make your life easy by doing a rudimentary programming of the radios, but it doesn't give you much flexibility.

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k4wtf
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Postby k4wtf » Thu Aug 07, 2003 8:06 pm

What we've done with amateur repeaters to eliminate the sq-tail is put a delay device inline to delay the audio from the RX to the TX by about 250ms. The TX is driven by pre-delay PL detection so, the audio now lags 250ms. This was just about right to kill off the sq-tail without killing off anything that was actually said.

It's not rocket science and I'm sure there is a much better way to do it but, this worked for us.

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Will
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Postby Will » Thu Aug 07, 2003 10:49 pm

The "squelch crash" or lack of squelch in the recieved audio used for the repeated audio is a normal thing, built into the design.
Check the jumper in the receiver radio that passes the SQUELCHED audio to the 16 pin connector. It may be set in the FLAT un-squelched position. I my desktracs, I rerouted the audio and the "tail" went bye bye.

Also make sure the squelch is adjusted properly in the receiver radio. It also depends weather the portables are sending the correct "reverse burst" to mute the repeater receiver.

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k4wtf
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Postby k4wtf » Thu Aug 07, 2003 10:59 pm

On the subject of "reverse burst", can someone explain it to me? Is it a selectable option on the radio? I haven't seen anything about this in Saber RSS.

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911_guy
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Postby 911_guy » Fri Aug 08, 2003 3:21 am

This may be a little oversimplified, but reverse burst sends out the same PL, but, as it was explained to me 180* out of sync to tell the repeater or the other radio "you can stop listening now, thank you for your time". Like I said, that's a little oversimplified, but I think that's about it.

Hope this helps.

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k4wtf
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Postby k4wtf » Fri Aug 08, 2003 4:13 am

After I posted my question, I went out and did a search on Google and found some information that explained it the same way. The way I understand it now, the reason for the 180-deg inversion was to stop the decoding reed from vibrating. I hadn't thought about it that way. I've always worked with solid-state PL devices though.

Anyway, our "delay" trick probably wouldn't work with the mechanical reed decoders.

Something I also found was that when using radios that don't support "reverse burst" on a repeater designed to use it, they suggest using PL "and" Carrier squelch, not just PL to trigger the transmitter.

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Will
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Squelch crash on the tail

Postby Will » Sat Aug 09, 2003 3:11 am

You are close, the "And" squelch setting is for the audio path to unmute requiring valid PL decoding AND receiver un-squelch. To correctly mute the receiver audio, the fact that either the correct PL or noise squelch activates muting the audio, that is OR setting...loosing either one OR the other mutes.
Some Motorola receivers have the problem that when the decoder "sees" a valid PL it forces the carrier squelch open and when the receiver looses the carrier the PL decoder is still decoding due to the slight delay in seeing the loss of PL, causing the burst of noise that can last for up to 1/2 second in some receiver/decoder combinations. So that is what makes the "squelch crash".

On the Maxtrac receiver or Radius, same animule, the And OR function is the usaual way it works. Check the jumper, if I remember JU551 for the correct position. If the RX audio going via the jumper to the transmitter is in the wrong position the audio at that point is NOT squelched at all, so during the loss of signal the PL decoder is keeping the transmitter keyed and when the TOS (Tone Operated Squelch) signal from the receiver which keys the dropout timer in the DEskTrac which is delaying the unkeying of the transmitter, the "unsquelched" audio which is just noise is still going into the transmitter and out on the "tail". The "tail" is the time of the drop-out delay and the transmitter's reverse burst.. 1 to 2 seconds + 145ms for the reverse burst.

Most of my repeaters do not "crash" and will mute fast enough, OR gating, to not get the noise even from a off brand radio's transmitter without the correct "reverse burst" or none at all.
On some radios the option, for "chicken burst"-- transmitter stays keyed for 180 ms without transmitting any PL tone, is available.


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