FPV image transmission knowledge and frequency selection

Obviously, the farther the better, so many people may think that it is true to choose high power. At the same time, the transmit power of the transmitter and the matching of an efficient antenna are very important. In fact, the transmission distance of the radio is a very big problem even in the profession. As an amateur player, there is no need to delve into it. You can simply think that under all conditions are unchanged, the transmission power increases by 1 and the distance increases by 0.5. However, on a model with limited load, space and energy, is it possible for you to install a high-power transmitter? Obviously it is impossible. In addition, even if you can install a high-power transmitter on the aircraft model, due to space restrictions and other equipment is very close, other equipment will be interfered with and cannot work normally, then the image transmission can be transmitted farther. What is the point? So you have already seen that most of the image transmissions for amateurs can be on the plane around 1W. Therefore, friends must use their ingenuity in this range, and use limited equipment to the limit.

Selection of FPV image transmission frequency

1. Frequency and distance

In the limited direct view range, the relationship between distance and frequency is not big, but one thing to note is that if the frequency of the image transmission and the frequency of the remote control overlap or interfere, it is another matter.

2. Frequency and interference

If you use 2.4G control, it does not mean that there will be interference if you use 2.4G image transmission, or there will be no interference with other frequencies. Here you need to know a little high-frequency expertise to make friends more understand. In fact, 2.4G usually means that the working frequency band is in the range of 2.4G, and the frequency points used by the devices in the 2.4G frequency band overlap with each other, or the interference frequency coincides with or is close to the operating frequency. Co-channel interference or adjacent-channel interference.

To transmit the signal, the high-frequency oscillator must first generate a fixed frequency. At the same time as the frequency is generated, many secondary frequencies are generated. These frequencies are often in the form of multiples of the main frequency. For example, if you want to get a 100MHZ signal In order to transmit the carrier wave to the FM radio, if you want to stabilize the frequency, use a frequency-stabilized crystal. If the crystal can be found only 10MHZ, you can use the 10MHZ crystal to oscillate and select its frequency to multiply it by 10. In this way, a signal with a frequency of 100MHZ is obtained, which is directly generated without amplification, and is a secondary frequency after 10 times. It can easily transmit tens of meters. If this is an interference signal, the distance is within 1 meter. It is impossible to work at all.

There is also a case where more complicated secondary waves will be generated. When two frequencies are added to the same circuit at the same time, +-×÷ various forms of secondary conversion waves will be generated between the two frequencies and the secondary frequencies. It is quite complicated, but the device is still working normally. Why is this? This is because the frequency selection circuit in the circuit is working, only allowing a certain fixed frequency signal to pass, or setting a corresponding suppression circuit at the main interference frequency. Interference is not likely to occur on the same device, because the secondary frequency is definitely different from the main frequency required, so rarely will you interfere with yourself, and when two devices, one of the generated secondary waves corresponds to the other. There must be something wrong with the frequency selected by the device. If it is close, it will not work. As the only device on the aircraft that generates frequency radiation, the amount and purity of the secondary waves generated by the image transmission itself is a key factor for the quality of the image transmission. In addition, the presence of secondary waves will disperse part of the transmitter power.

According to the above analysis, 1.2G and 2.4G are the most controversial among the several frequencies of common image transmission. Some people say that 1.2G will interfere with 2.4G control, and some people use it without problems, so they object to saying that It’s a rumor, it’s just a trivial matter. In fact, 1.2G or 2.4G are all talking about the frequency bands they work in. Now I know that they will only be interfered if there is a coincidence in the frequency of the operation. If you have just read the frequency and interference above, Introduced, maybe now understand that 1.2G or 2.4G is indeed possible interference, this possibility is much greater than other frequencies, so a friend suggested that it is best to avoid these two frequency bands makes sense.

3. The relationship between modulation and distance

The distance of the image transmission is not as long as the distance of the remote control. This involves the problem of bandwidth. This problem is a bit more complicated. Just a friend of the game can know it. When the remote control transmits information, the signal simply needs only one point. Okay, the energy is relatively concentrated, and the frequency of the video signal ranges from 0-8M. After adding it to the transmitted signal, it needs 8M of bandwidth (main frequency signal +-4MGHZ). This is why the frequency interval of the TV station is 8M. , And the radio station can set a frequency point with only a few M. The bandwidth is wider to disperse the signal energy, and it is natural that the same power image transmission is closer than the remote control distance.

4. Other factors

We have talked about some theoretical things in the front. The other is the problem of the hardware itself.  It is difficult to visualize. This is mainly related to the positioning of the producer and the quality of the components used and the circuit design. In addition, in terms of interference due to frequency overlap, the higher the frequency, the less use, so the same frequency interference will be less, but under the same circumstances, the higher the frequency of the components, the more expensive.

5. AV format

The video AV signal output by the camera has already determined the standard. For the image transmission, the general image transmission equipment, what type of video AV signal is input, and the corresponding standard signal is emitted. The low-end image transmission equipment is basically like this It is the most important image transmission design that many people have received. For the image transmission equipment with standard conversion function, it is often more professional and the cost is higher. When using this type of equipment, you need to pay attention to the consistency of the signal between the input and output, and try to avoid multiple signal conversion.

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