CTCSS-DCS Subtones

Sub tones are sent out with the voice transmission and are used to open only those receivers that are tuned to the same sub tone. In this way, entire groups or just individual devices can be addressed. At the receiver, the squelch can always be completely open, since only signals that are sent at the same time as the sub tone can get through.

For the duration of each transmission, the transmitted speech is underlaid in the transmitter with a possible identifier in the form of a digital data stream. In contrast to the conventional squelch, which switches on the receiver's loudspeaker when each signal is received, this is only activated when using DCS if the data stream is also recognized with a previously defined possible identifier. In this way, the recipient only receives those messages that a sender has provided with the identifier he expects. The data stream transmitted at the same time as the speech is made inaudible for the user in the receiver. Since the corresponding signal is outside the audio frequency range used for speech transmission, it can be filtered out easily and effectively.

In principle, individual devices could also be addressed in this way by using the identifier expected from them when sending out. In fact, however, it is the case that much simpler and more flexible systems with larger address spaces, i.e. a larger number of individually addressable radio devices, such as 5-tone call, DTMF and the technologies MODAT, MDC-1200 and Quik Call are available.

DThat sounds pretty good at first, if… yes, if not.

The CTCSS tone does not protect against interference present on a frequency, the DCS system fails even in such a case.

Here two examples Radio operator A is talking to radio operator B both have CTCSS tone on for transmit and receive.

1.    Both are surprised that interference affects the quality of the QSO.

2.    The QSO keeps dropping out because interference is deleting the sub tone.

In both cases it was not noticed that a second QSO on the frequency used was conducted with or without a different CTCSS tone.

CTCSS-DCS sub tones are already standard in the equipment of Freenet and PMR devices in the lower to middle price range. With CB radios, on the other hand, this function still leads a shadowy existence. It is therefore almost pointless to work with sub tones at CB Funk, since too few users have the appropriate devices.

The number of different sub tones also makes it difficult for other radio friends to get into an ongoing conversation. After all, you don't even know that a subtone and if any, which one is used. Of course, that can be intentional, but it's actually not the point of public radio.

Something different it looks at Gateway operation. Here it is usually known which sub tone is used. However, if this is not the case, the user also has a problem in reaching the gateway. The same applies to relay operation.

Another function in the devices would help, namely the CTCSS/DCS scan. Of course you can try every tone by hand, but by the time you've gone through them all, the conversation you want to join is probably over.

In the case of local rounds, it would still be a possibility that at least one radio friend has not set a subtone on the receiver side. This would then also hear every other station and could point them to the use of a CTCSS-DCS sub tone.

However, this would in turn require the device to be able to set the sub tones separately on the transmit and receive side.

Conclusion

CTCSS and DCS are like selective noise blocking, they cannot separate QSOs that are performed on a frequency. Only digital radio systems such as dPMR or better DMR with TDMA can do this. The disadvantage of using CTCSS and DCS for sending and receiving is that a free frequency is played although other users are currently using it because there is usually only a visual display. Switching on the function blocking of transmission (BUSY LOCK, BCL) is necessary here in order to prevent other QSOs from being disturbed. When operating with a gateway, it is recommended to only use the tones for sending, just like with a front door on one side there is a blade anyone can go through and the other side only opens the door with the key, the user hears interference in this way or a QSO not coming from this one.  

In my opinion, the manufacturers are the first to be challenged. These should basically install the subtone function in such a way that the tones can be set separately on the transmitting and receiving side. In addition, the devices should have a CTCSS/DCS scan and the function should not only be adjustable via umpteen submenus. Furthermore, all devices should have the same list of CTCSS and DCS tones, otherwise, as was previously the case, one device can do the sub tone but the other cannott.

The dealers are then asked to point out this function when purchasing the devices. The inexperienced customer may have never heard of it and it would be very helpful for him if he were specifically informed that this function may be used by other radio stations. Advertisements that make x times more from 8 or 16 channels via this function are not helpful. Of course, the individual radio operator is also required to switch off his sub tone to give inexperienced radio friends the opportunity to get in touch with him. Radio broadcasts and clubs could announce their sub tones on the homepages (if available). I believe DCS and CTCSS will also gain in importance in CB radio. Gateways and relays will no longer be able to do without them. In the other areas, digital operation will become more and more popular, making the sub tones superfluous