Audio Muting Using (Non) Selective Calling
Posted: Thu Oct 27, 2011 9:27 am
Since posting this article I've finally got around to testing the effect of the FFSK Lead in delay which was removed from the PTT release aspect of the original configuration file. This is a check box on the Data/GPS page called 'Use LID for FFSK ANI' The attached document advises that this checkbox is left unchecked but if silent GPS data is needed then it's now been confirmed that checking this box using the values shown in the screen shot will work to produce completely silent GPS. This has been tested using all forms of polling via MRMap including clicking the asset panel icon. It's also been tested via a TSF2025 repeater without any problems. The only audible parts of the transmitted signal are the spoken voice and a single short beep on the end of the transmission. This is the selcall letter 'C' which is the 'Close Mute' sequence. For a closed group communications system where outsiders would not be expected to require access then this is an extremely effective voice and data muting method.
This system isn’t really for use on the UKSAR channels unless every team in the country adopted the same selcall tone sequence. It’s described here for those teams who use private channels for one reason or another, Crag Radios, SARDA with the UK-General channels or cross-band link frequencies that might be used elsewhere in the area by taxi companies etc and cause you some interference. The term 'Selective Calling' is slightly misleading as that's exactly what this system isn't. All radios programmed using this method will talk to each other without any button pushing being needed. What they won't do is hear anyone else....at all. The selcall tone sequences are the same in all radios and are used only to open and close the audio mute gate. In a way it's a sort of super CTCSS where the 38 odd available CTCSS tones are augmented by the thousand upon thousand available selcall tone sequences. The chances of these being duplicated by another organisation are very slim indeed. If you need to ensure that no outside interference is received by your radios during a particular operation, crag work being the one that comes to mind, then one of the UK-General (Business Simple, I think they're called now) channels can be programmed using this system. Unless called by a radio programmed in exactly the same way, they will hear nothing at all.
The selcall 5-tone sequence used to open the audio mute gate isn't heard by the receiving radio but the single tone that closes the gate is heard as a 'roger beep'. Basically any team members involved in crag work can be assured that if they heard their radio make any sound then it was intended for them as no one else can talk to them on that particular channel.
It's worth mentioning that because MRMap doesn't send the correct selcall sequence when it polls team radios and nor do the team radios send the tones when they reply to a group poll, GPS poll requests or replies are completely silent. This would lead me to assume that if the 'Use FFSK LID for ANI' option box is checked then all GPS would be handled in complete silence. The radio itself still receives the FFSK data, it just doesn't open the speaker mute because the selcall tones haven't been received. Whether you hear the FFSK or not is of no interest to the radio, it processes the data as normal and you appear on MRMap as normal, just in silence apart from the single beep as the reset tone is sent and received. In the case of crag work, the location of the team members involved is still being sent to MRMap but they aren't now aware of it and operate in peace and quiet until someone actually speaks to them.
Largely produced as an exercise for another organisation, this might find a use within mountain rescue.
This system isn’t really for use on the UKSAR channels unless every team in the country adopted the same selcall tone sequence. It’s described here for those teams who use private channels for one reason or another, Crag Radios, SARDA with the UK-General channels or cross-band link frequencies that might be used elsewhere in the area by taxi companies etc and cause you some interference. The term 'Selective Calling' is slightly misleading as that's exactly what this system isn't. All radios programmed using this method will talk to each other without any button pushing being needed. What they won't do is hear anyone else....at all. The selcall tone sequences are the same in all radios and are used only to open and close the audio mute gate. In a way it's a sort of super CTCSS where the 38 odd available CTCSS tones are augmented by the thousand upon thousand available selcall tone sequences. The chances of these being duplicated by another organisation are very slim indeed. If you need to ensure that no outside interference is received by your radios during a particular operation, crag work being the one that comes to mind, then one of the UK-General (Business Simple, I think they're called now) channels can be programmed using this system. Unless called by a radio programmed in exactly the same way, they will hear nothing at all.
The selcall 5-tone sequence used to open the audio mute gate isn't heard by the receiving radio but the single tone that closes the gate is heard as a 'roger beep'. Basically any team members involved in crag work can be assured that if they heard their radio make any sound then it was intended for them as no one else can talk to them on that particular channel.
It's worth mentioning that because MRMap doesn't send the correct selcall sequence when it polls team radios and nor do the team radios send the tones when they reply to a group poll, GPS poll requests or replies are completely silent. This would lead me to assume that if the 'Use FFSK LID for ANI' option box is checked then all GPS would be handled in complete silence. The radio itself still receives the FFSK data, it just doesn't open the speaker mute because the selcall tones haven't been received. Whether you hear the FFSK or not is of no interest to the radio, it processes the data as normal and you appear on MRMap as normal, just in silence apart from the single beep as the reset tone is sent and received. In the case of crag work, the location of the team members involved is still being sent to MRMap but they aren't now aware of it and operate in peace and quiet until someone actually speaks to them.
Largely produced as an exercise for another organisation, this might find a use within mountain rescue.