White Paper on UAV Interference Technology Based on VCO DDS and SDR Technology (2)
- Introduction to Electromagnetic Interference Technology
The purpose of all interference is to prevent the enemy from effectively using the electromagnetic spectrum. In electronic warfare, electromagnetic interference is also known as electronic countermeasures. The basic method of electromagnetic interference is to send the interference signal along with the signal expected to be received by the enemy into the receiver, making it impossible for the enemy receiver to obtain correct information.

Figure 9 Communication Link and Interference Link
Common electromagnetic interference methods include suppression interference,
deception interference, and intelligent interference.
Suppressive electronic interference
Suppressive electronic interference refers to interference that causes overload, saturation, or difficulty in obtaining useful signals in the receiving system of enemy communication equipment by transmitting interference signals. Suppressive electronic interference can be simply divided into the following categories:
1. Blocking interference: Blocking interference, also known as blocking interference, has a wide spectrum of interference radiation and can usually cover the entire operating frequency band of local communication stations. Its advantage is that it does not require frequency coincidence equipment or reconnaissance equipment to guide interference. The equipment is relatively simple and can simultaneously suppress multiple communication stations within the frequency band. But its disadvantage is that the interference power is dispersed and the efficiency is not high; Secondly, when applying blocking interference, the own signal that falls within its frequency band is also interfered with.
2. Targeted interference: Targeted interference refers to the sum of the carrier frequency of the interference and the frequency of the signal, or the interference signal and the communication signal having the same frequency spectrum width.Usually, each interference frequency is aligned with a corresponding communication signal frequency to implement interference, but there are also application cases where one machine interferes with multiple targets.
3. Sweep frequency interference: Sweep frequency interference refers to the interference formed by the continuous variation of the carrier frequency of the interfering transmitter from low to high or from high to low in a wide frequency band in a certain way.
Deception jamming
Deceptive interference refers to a type of interference that uses communication simulation equipment or jamming equipment to transmit signals that match the characteristics and timing of communication signals, deceive communication links to produce unexpected responses, and achieve system attack targets that restrain, isolate, and occupy spectrum resources, or cause communication users to engage in erroneous behavior to achieve tactical goals.
Intelligent interference
Intelligent jamming machines have real-time situational awareness, learning, decision-making, and other capabilities for target communication systems, and can adapt to different electromagnetic environments and respond to different jamming objects. Starting from tactical objectives, through multidimensional cognition and learning of time-frequency air power, waveform, network, and system, different optimal decisions are formulated and executed to achieve the most efficient, cost-effective, and dynamic interference.
3.UAV interference circuit architecture
VCO Sweep frequency jammer
VCO A sweep frequency jammer is a simple jammer architecture. The following figure shows the principle of a channel jammer. Firstly, a triangular wave generator generates a triangular wave with a frequency of several tens of KHz, which drives the voltage control terminal of the VCO. This allows the VCO to output a swept frequency RF signal, which can then be transmitted through an amplifier and antenna

图10 VCO 扫频式干扰器原理
Due to the discreteness of the characteristics of VCO devices, frequency adjustment is required for each channel of each VCO type jammer; At the same time, as the output frequency of VCO varies with temperature, a certain protection bandwidth needs to be reserved to avoid VCO frequency drifting out of the range of interference.
DDS Sweep frequency jammer
The principle of DDS sweep frequency jammer is shown in the following figure. DDS (direct digital synthesizer) directly generates a sweep frequency signal with a certain bandwidth (for example: 200~300MHz), then mixed with the local oscillator signal, and filtered out by a bandpass filter to obtain the desired RF signal (e.g.:2400~2500MHz), amplified and output by the antenna.

Figure 11 Principle of DDS Sweep Frequency Jammer
The frequency source of DDS sweep frequency jammer comes from DDS and local oscillator, and the frequency accuracy of DDS and local oscillator comes from the reference crystal oscillator. Therefore, the frequency accuracy of DDS sweep frequency jammer can be very high (depending on the reference crystal oscillator). Compared with VCO sweep frequency jammer, DDS sweep frequency jammer does not need to consider additional protection bandwidth and can accurately define the sweep frequency range.
The circuit of DDS sweep frequency jammer is more complex than that of VCO sweep frequency jammer, and the filter model and size are also different when the output frequency is different, so the normalization degree of the circuit will be slightly lower.
SDR technical jammer
The principle of the jammer based on SDR technology is shown in the following figure. The FPGA loads the waveform file stored in Flash into DDR, and then sends the waveform file to the digital baseband interface. After passing through the IQ modulator, it becomes the RF signal of the target frequency band, which is then amplified by an amplifier and output to the antenna. The IQ modulator integrates a local oscillator source and can change the local oscillator frequency through SPI encoding.
Figure 12: Principle of Interference Device Based on SDR Technology
Based on SDR technology, jammers can transmit any signal within a certain bandwidth, such as single tone sine signals, simple modulation signals, or OFDM signals. The type of signal is completely defined by software, so specific interference signals can be used for specific communication signals to achieve the best interference effect.
We call this specific interference signal interference code. Depending on the encoding method of the communication link, different interference codes can be selected. For example, if the communication link uses a single carrier QPSK modulation signal, we can choose the corresponding single carrier QPSK interference code. If the communication link uses OFDM signals, we can choose OFDM interference codes with the same subcarrier spacing.
1. Evaluation of drone interference effect
sweep frequency jammer
Both VCO based and DDS based jammers are based on frequency sweep technology. When using frequency sweep based jammers to interfere with unmanned aerial vehicle communication protocols (taking OFDM modulation multiplexing communication protocols as an example), the corresponding physical layer data blocks will be interfered with, causing the communication link to be completely interrupted. Therefore, frequency sweep jammers often require a large transmission power to interfere with unmanned aerial vehicle communication links.

Figure 13 Interference of Sweep Frequency Jammer on UAV Communication Link
SDR Jammer
Based on SDR technology, the jammer can cover the entire frequency band and achieve blocking interference; It is also possible to selectively cover only a small portion of the frequency band to achieve targeted interference, allowing energy to be more concentrated and interference distance to be farther. Regardless of the interference method, all subcarriers of the interfered OFDM signal can be interfered with, with an error rate close to 100%. Even with strong error correction coding mechanisms, it is difficult to recover data at such a high error rate. Therefore, SDR style jammers can effectively interfere with drone data links.
Figure 14 Interference of SDR type Jammer on UAV Communication Link
SDR type jammers can also emit sweep signals within a certain bandwidth, and the sweep speed will be faster than VCO type and DDS type jammers. For remote control protocols such as ELRS with frequency hopping function, the entire frequency band can be fully covered to achieve blocking interference.
Summary
VCO DDS SDR use comparative analysis |
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Project |
Interference method |
jammer effectiveness |
Cost |
Class |
VCO |
sweep frequency jammer |
It is necessary to target the frequency and have a significant impact effect. It is currently the most commonly used method of drone interference; It has been extensively used in practical combat. |
VCO implementation is easy and the product cost is low, but it needs to be frequency specific; |
military/civil |
DDS |
sweep frequency jammer |
Need to focus on frequency, with less practical experience. The striking effect is obvious. |
Broadband output is difficult to implement and has a very high cost of use, but it has a wide output frequency and can be portable. At the same time, it can seamlessly cooperate with frequency detection units, which is the main development direction in the later stage; |
military/civil |
SDR |
Blocking interference |
High precision detection units are required, along with a complete application wireless transmission database and corresponding radio characteristic codes, in order to effectively carry out interference; Good interference effect. |
The main mode of electronic warfare is difficult to develop and has extremely high usage costs |
military |
In summary, considering both cost and output channels, the VCO anti drone solution will remain the mainstream mode of drone interference for a certain period of time in the future. If full frequency coverage is achieved on the signal source VCO, it can better meet the actual needs on site.