Continuous Tone on 451.x and 456.x when not in use

Cantafordit

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Sep 6, 2017
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11
Location
Cork, Ireland
Hi everybody, I hope you can help. I am in Ireland and our national rail operator uses a number of paired frequencies in the 451 and 456MHz range but they all have a very annoying continuous tone when the channels are not in use. Once a radio is keyed I can hear one side of a conversation and then back to this high pitch tone. I can't find any information online about the system they use, only that they are moving to GSM-R. Is there a way to ignore the tone and only activate the scanner when there is speech. I have a Uniden SDS100. I have had to 'avoid' these channels because the scanner stops on the tone every time. Any help would be appreciated. thank you.
 

R8000

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Premium Subscriber
Joined
Dec 19, 2002
Messages
742
I don't know how their radio system is setup, but it sounds like you are listening to a RF linked receiver site that sending status tone to a voter. 2175 Hz was a standard used in North America by Motorola for decades.

2175 Hz
 

Ubbe

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Sep 8, 2006
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5,040
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Stockholm, Sweden
We had the same type of system here for railroad. The radios are scanning for that tone and it was different ones depending of the location. When it found the same tone the radio where set to it stopped scanning and monitored the quality of the tone. If it got too noisy it started to scan the channels for another frequency with a better signal strenght.

When the trains got GSM-R some 10-15 years ago they removed that system and now the work personel also use a mix of analog and DMR radios.

The data skip function on some older scanners could be used, but you would still hear that tone for a second until it started to scan again. If I remember correctly the AOR AR8200 could be set to ignore the tones, or if it needed an addon pack called Tone Eliminator or something.
Some Icom receivers have audio notch filters, and probably other receivers as well, that can be set to notch out that tone from the audio.

/Ubbe
 

ecps92

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Joined
Jul 8, 2002
Messages
11,419
Location
Taxachusetts
when they talk is there a PL or DPL displayed in your tone search ??
Hi everybody, I hope you can help. I am in Ireland and our national rail operator uses a number of paired frequencies in the 451 and 456MHz range but they all have a very annoying continuous tone when the channels are not in use. Once a radio is keyed I can hear one side of a conversation and then back to this high pitch tone. I can't find any information online about the system they use, only that they are moving to GSM-R. Is there a way to ignore the tone and only activate the scanner when there is speech. I have a Uniden SDS100. I have had to 'avoid' these channels because the scanner stops on the tone every time. Any help would be appreciated. thank you.
 

Cantafordit

Newbie
Joined
Sep 6, 2017
Messages
11
Location
Cork, Ireland
Thank you for the replies guys, I don't think there is a PL or DPL displayed, I'll have to look at it the next time I hit that frequency and there is talking.
 

mmckenna

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Jul 27, 2005
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Location
SNCZCA01DS0
Thank you for the replies guys, I don't think there is a PL or DPL displayed, I'll have to look at it the next time I hit that frequency and there is talking.
Some repeaters will strip off the PL/DPL when it sends the traffic out to the rest of the system. I agree, sounds like a classic tone remote system over RF.
 

Ubbe

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Sep 8, 2006
Messages
5,040
Location
Stockholm, Sweden
The tones in our system where according to the ZWEI systems tone table. District 1 used tone 1 which where 1060Hz and district two used tone 2 at 1160Hz and so on. The normal modulation level for the tones where usually 3,5KHz but in this system they where reduced to 2Khz so that they where more easily interfered from background noise and would start hunting for another channel before it got too bad for voice communication.

/Ubbe
 
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