Sub-audio, direct frequency, reverse frequency

Date:Jan 22, 2021


Sub-audio is a method used to prevent interference from unrelated stations when there are multiple stations communicating on the same frequency. There are many types of sub-audio. The most commonly used sub-audio is CTCSS (Continuous Audio Code Squelch System). Motorola is called PL. It belongs to analog sub-audio. The frequency ranges from 67.0 Hz, 69.3 Hz, and up to 250.3 Hz, with a total of 39 sub-audios. Audio points (or 50 points). When transmitting, this low-frequency inaudible signal (hence the name sub-audio) is continuously superimposed on the frequency for transmission. The other party will only receive it when receiving the same frequency for anti-interference, or not listening to the signal that is not for yourself. .

The sub audio is divided into two types: transmitting sub audio and receiving sub audio. Generally, in order to be able to access the relay, the transmission sub-audio is used, so that the relay can be turned on. The relay itself uses "receiving sub-audio", and signals without sub-audio are rejected. Some of the relayed signals do not have sub-audio but some have sub-audio.

Similarly, in order to reject signals that you don't need to listen to when you receive, you can also add sub-audio to the receiver. In this way, two radio stations (or several radio stations) can also use the agreed sub-audio frequency to eliminate external interference signals.

Although it is said to be sub-audio, it is actually audible, especially when the sub-audio is set at a high limit (near 250Hz), or when the receiver's low-frequency frequency response is relatively good. Therefore, when we set the sub-audio, set it as low as possible to avoid unnecessary interference.

Another kind of sub-audio is DCS (DigitalCoded Squelch), which belongs to digital sub-audio. Motorola is called DPL. It has 104 sub-audio points (DPL is less). It is more advanced. It uses digital coding before speech and before transmission. emission. This kind of sub-audio can only transmit and receive at the same time (that is, it cannot be set to only transmit without receiving).

Direct frequency

The so-called direct frequency refers to the situation where two radio stations communicate with the same frequency. For testing purposes, many enthusiasts do not use the relay when there is a relay, and directly use the downlink frequency of the relay, that is, the listening frequency for communication.

Direct frequency connection has the characteristics of good signal (no relay), small influence range, no interference to the relay, and no change to the relay listening, so it is suitable for short-distance communication.

For example, the uplink frequency of a relay is 434M, and the downlink frequency (that is, the listening frequency) is 439M, and the direct frequency is 439M for both sending and receiving. After one party adopts direct frequency, it is recommended that the other party also change to direct frequency. Otherwise, although the two parties can communicate, the signal of the other party is relayed down, which still affects the overall situation and sounds strange to only one party. When both parties use direct frequency, the relay signal is still monitored during the gap between the connections.

 reverse frequency

The so-called frequency scrambling is a communication method in which one party does not use the relay when there is a relay, but uses the two transceiver frequencies used by the relay in reverse. Also called "inverse frequency".

Reverse frequency connection has direct signal (without relay) and does not change the way the other party uses relay, so it is suitable for direct connection test without the other party knowing it.

For example, the uplink frequency of a relay is 434M, and the downlink frequency (i.e., the listening frequency) is 439M. After we use the frequency scrambling, it will receive 434M and send 439M. In this way, our party directly listens to the upstream frequency of the other party instead of the frequency from the relay, and the other party receives our direct frequency and not from the relay, because our party has not opened the relay at all.

The advantage of this is that the other party can still use the relay mode without changing any settings, and can test the direct connection between the two frequencies. Scrambling is also often used to check the strength and quality of the other party's uplink signal.

The weakness of this approach is that only one party's signal appears in the relay, which is weird. But if the monitor is close to the scrambling user, he can receive the direct frequency transmission at the same time. Generally speaking, if you find that the reverse frequency connection is very smooth, you can change to direct frequency connection and let the relay out.

Some walkie-talkies are equipped with shortcut keys to facilitate the reversing operation, making it easy to use reversing in the relay operation.