What is repeater, frequency, frequency difference, sub-tone, direct frequency, reverse frequency

Date:Jan 07, 2021

1. What is a relay?

    Due to the obstruction of buildings/terrain, etc., the signals between the two stations on the ground may not be able to transmit to each other. Usually a 5W mobile phone cannot be connected in the urban area 2 kilometers away. For this reason, people set up an antenna at a high place and set up a high-power special transceiver station, which is responsible for forwarding the signal received on one frequency point (such as 434.460) to another frequency point (such as 439.460), so it is All stations within the coverage area can contact it, that is, to communicate with other people through it, so everyone can use the repeater to achieve a wider coverage range and help low-power devices expand the signal.

    Usually a repeater station needs to use a pair of frequency points, one frequency point is used to receive the signal from the user’s hand or car (uplink signal, such as 434.460), and when received, broadcast on the other frequency point ( Downlink signal, such as 439.460). Since the relay station occupies a better geographic location and has a relatively large transmission power, more people can be contacted through the relay station. The transmitting and receiving frequency of the hand or car of the person who uses the relay must be opposite to that of the relay before the relay can be turned on.

2. What is frequency?

    Usually we refer to the downlink frequency. The so-called "uplink" frequency refers to the transmitting frequency of the radio station, and the corresponding "downlink" frequency is the frequency transmitted by the relay station, which is the receiving frequency of the radio station (i.e., the listening frequency). Because the "downlink" frequency is generally used to indicate the frequency of a relay, the downlink frequency is generally called the surface frequency, and the corresponding uplink frequency is called the "base frequency".

3. What is frequency difference?

    "Difference". Generally, when using relay equipment to communicate, different transmitting and receiving frequencies are used. The frequency difference between the receiving frequency and the transmitting frequency is called "difference frequency", and the difference frequency is divided into upper difference. Sum and drop, generally we use drop, that is, the transmit frequency is lower than the receive frequency. Take 460 relay as an example: the transmit frequency is 434.460, the receive frequency is 439.460, the difference between the two is 5MHz, we call it 5MHz, This is the setting method of a general amateur radio station, because some amateur radio stations have a fixed difference frequency, which is 5MHz. Of course, there are some places where the difference frequency is set special. For example, some relays in Hong Kong are set to 9.850MHz.

4. What is sub-audio?

    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 kinds of mute tones. The most commonly used subtone is CTCSS (Continuous Audio Coded Squelch System). Motorola is called PL, which belongs to analog subtones. The frequency ranges from 67.0Hz, 69.3Hz, and up to 250.3Hz, with 39 subtones Tone points (or 50 points). When transmitting, the low-frequency inaudible signal (hence the sub-tone) is continuously superimposed on the frequency to be transmitted. The other party will only receive it when receiving the same frequency, which is used for anti-interference, or not listening to the signal that is not for yourself. .

    There are two types of sub-tone: transmitting sub-tone and receiving sub-tone. Generally, in order to be able to access the relay, transmit subtones are used, so that the relay can be turned on. The relay itself uses "receiving subtones", and signals without subtones are rejected. Some of the relayed signals have no sub-tone but some have sub-tone.

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

    Although it is said to be sub-tone, it can actually be heard, especially when the sub-tone is set at the high limit (near 250Hz), or the low frequency response of the receiver is better. Therefore, when we set the sub-tone, we try to set it as low as possible to avoid unnecessary interference.

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

Misunderstanding: When transmitting sub-tone, the receiver can only receive when set to sub-tone reception. wrong! In fact, the opposite is true. When transmitting sub-tone, the receiver must be able to receive it when it is set to "non-subtone receiving state". When it is set to "subtone receiving state", the subtone type and the subtone code must be consistent to receive.

5. What is direct frequency?

    The so-called direct frequency is the sobriety that two radio stations communicate with the same frequency. For testing purposes, many hams 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.

The 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 both parties can communicate, the signal of the other party is relayed, which still affects the whole situation and it sounds strange that only one party is speaking. When both parties use direct frequency, the relay signal is still monitored during the gap between the connections.

6. What is scrambling?

    The so-called frequency scrambling is a connection 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's awareness.

    For example, the uplink frequency of a relay is 434M, and the downlink frequency (i.e., the listening frequency) is 439M. After we use scrambling, we will receive 434M and send 439M. In this way, our party directly listens to the other party's uplink frequency 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 at the same time 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.

    *Reverse frequency is usually used to check whether the signal strength of the other party directly is sufficient, so as to determine whether the two parties connected are within the range of direct frequency communication, so as to switch to direct frequency communication. The source of interference can also be located! Looking for malicious interferers, some walkie-talkies are equipped with shortcut keys to facilitate the re-frequency operation, which makes it easy to use the re-frequency in the relay operation. This feature is very common on Yaesu and Kenwood hand stands.