Chapter 248 Frequency Division Multi-channel, Avoiding High-Specification Components
Seeing this, the rest of the people gathered around the table.
“If the dual-channel signal uses an orthogonal design, it can essentially double the instantaneous bandwidth. Although compared to single-channel DRFM, the performance requirements for ADC and RAM have been reduced. But this is still not thorough enough.”
“But we can consider abandoning the idea of phase-divided sampling or time-divided sampling and designing multiple narrow-band DRFM subsystems, split according to frequency bands, and each channel is connected to a voltage. The controlled oscillator (VCO) is then mixed, and the output baseband analog signal is processed by a narrow-band DRFM subsystem, so that the bandwidth requirements for DRFM can be almost completely avoided, and the sampling frequency can also be reduced to a fraction of the original. "
At this time, the pencil in Chang Haonan's hand seemed to Guo Lin like a magic wand. The intersection between the tip of the pen and the paper continued to produce miracles as the former drew pictures.
The circuit principle this time was more complicated, so Chang Haonan spent a while drawing it before finally completing it.
“This design is indeed feasible in theory, but if so much hardware is added to the project, each new part will bring system errors, and the superimposed noise floor and signal distortion will inevitably Very serious.”
Compared to Guo Lin, who was still analyzing the schematic diagram, Xu Yang had already begun to think about the feasibility of this idea:
“If nothing else, these few The inconsistency between channels requires phase level compensation. For dual-channel systems, you can also consider sharing a reference clock to achieve inter-channel coherence. Although this avoids the need for high-specification ADCs and RAMs, the increase in the number of channels will The requirements for reference clocks will increase again, but we still can’t build this thing.”
“The multi-channel technology that uses reference clocks you mentioned is generally used on oscilloscopes, and the DRFM architecture of the jammer is better than that of oscilloscopes. It’s much more complicated. Not to mention us, Americans probably can’t take this route just by relying on clock performance.”
The reason why this idea is considered feasible by the system is naturally because Chang Haonan has already considered this issue.
“So what we have to do next is to compensate for various error factors respectively.”
“For example, we can use a combination of calibration and compensation to distort the sampled data at the baseband Correction, suppress the amplitude-frequency characteristics and group delay characteristic errors in each channel to ensure that the reconstructed signal is close to the original signal. "
"What about the phase difference problem?"
< br>“There are not many tricks to the phase difference, but it can be measured, or very accurately estimated, so that corrections can be made in advance.”
Chang Haonan explained while writing in the astonished eyes of those around him:
“Suppose we send a broadband pulse signal with a slope k through the digital-to-analog converter, and the signal reaches the RF input end through the feedback branch. After filtering, band-pass filtering, down-conversion, and low-pass filtering, the DAC collects it into the signal processor and performs STRETCH deslope processing on the original transmitted signal. Due to the delay difference between the two signals, a single signal will be obtained. Frequency output Δf, this frequency can basically represent the delay amount in the input-input process: Δt=Δf/k. ”
“Is it...that simple?”
The one next to it. An engineer was surprised to find that he could understand.
He originally thought that he would be faced with a set of theories that were like a bible, and then he would need to go back and study for a few days to understand it.
"I'm just going to talk about the principle now. It's definitely simple, but later we need to consider the compensation algorithm in detail, and the workload is still quite big."
Chang Haonan put down his pencil and shrugged. Guo Lin next to him was very excited. The discerning man handed him a cup of tea at the right temperature.
Passing tea to the boss.jpg
“Chang Gong takes a sip of water.”
Chang Haonan picked up the cup and drank it all in one gulp:
"Of course, even under the most ideal conditions, it is impossible to completely eliminate the errors between multiple frequency bands. Especially for broadband cross-channel signals, the signal distortion generated at the intersection point of the frequency bands must exist in principle. , and the more they are stacked, the more they are, so we cannot make it unlimitedly with twenty or thirty channels, otherwise we may not even be able to pass the power-on self-test.”
“My current plan is to use what we can. The 350Mhz bandwidth DRFM that has been developed and can be stably packaged has 10 parallel channels, so that even if the bandwidth loss at the frequency band junction is included, the bandwidth coverage of about 2.5Ghz can be basically achieved.”
“That’s it. There are quite a few..."
The main business of Institute 14 is radar, so it is naturally sensitive enough to this kind of thing:
"As long as it can cover the frequency range of 6.5-9Ghz, It is enough to handle the C-band and X-band signals used by most air radars.”
Although the center point of the X-band is 10Ghz, considering the attenuation problem, in fact most radars will not use too high a frequency. 9Ghz is enough, and in the field of communications, the lower edge of the X-band will extend to 7Ghz. Nearby, the 6.5-9Ghz option can also provide precise directional interference to certain specific satellite communications.
“If the reconstructed signal compensation algorithm is good enough, there should be potential in this area.”
Xu Yang can still keep up with Chang Haonan’s ideas in his own field of expertise. .
“The biggest problem now is that the size and weight of the equipment will be larger than the dual-channel orthogonal design, and it is also difficult to control the heat and power consumption. I want to make it like L005 without occupying a heavy load. You don’t have to think about the self-defense pod. Fortunately, the performance of our thing is much better than the L005. If there are two of them on an aircraft in a formation, it can basically protect the entire fleet.”
Chang Hao. Nan casually drew a flat and long pod on the paper, and then drew a small fan-like thing on the head:
"However, we are still using it on the plane anyway. Adding an impact generator on the head can solve some of the power supply problems. As for heat dissipation, it can also be solved by introducing low-temperature air conditioning into the air."
said He drew an outline similar to an airplane on the paper, but his drawing skills were so average that people couldn't tell whether it was a J-8C or a J-H-7.
"In this case, do we have our own EA6B or EF111?" Looking at the concept map on the paper, an engineer standing behind Guo Lin suddenly said, with a tone of Full of joy.
It can be said that since the Gulf War a few years ago, for radar researchers like them, the above two types of dedicated electronic warfare aircraft have become their thoughts and hopes day and night. The defeated devil.
Although they still haven't completely figured out a way to defeat the enemy, but now...
Can they be considered to have created their own big devil?
"Well... Just talking about our pod, forwarding frequency shift interference belongs to the current mainstream technology route, and it is not bad in terms of function."
Chang Haonan looked in front of him. The outline diagram on the draft paper answered:
“But if you really want a dedicated electronic warfare aircraft, you will need to make major changes to the aircraft platform itself. Just two pods on an ordinary fighter aircraft is not enough. Meaning.”
"However, on the bright side, our imaginary enemy does not pay much attention to the construction of air defense systems due to its confidence in its air force. Therefore, the intensity of air defense suppression operations faced by our army is not as high as that of EA6B."
< br>In fact, having two such pods mounted on the J-8C or J-H-7 is closer to the effect of the F16CJ Wild Weasel in the US military.
Of course, even this is enough to make School 14 happy for a long time.
Although he has been reborn for nearly a year, Chang Haonan is still subconsciously accustomed to directly comparing the things he creates with powerful enemies on the other side of the ocean.
But for most people such as Guo Lin, this is something they would not dare to think even if they are optimistic.
To be able to achieve "the enemy is strong and we have it" instead of "the enemy has it and we have nothing" is already a dream that many people hope to realize throughout their lives.
But there are not exceptions.
As a person of this era, Xu Yang’s thinking is much broader:
“It’s a pity that this set of tools has only limited flexibility in processing broadband signals, and can only distribute them equally to each channel. Resources, there is no way to flexibly allocate frequencies to a specific narrowband frequency band based on the detected radar signal characteristics..."
Next to me, Chang Hao Nanxin said that you still dare to think, this is in the later EA6B This function is only implemented on third-generation electronic jammers such as and EF18G.
However, he did not want to make the comrades of the 14th Institute think that the role of more advanced components could be replaced by architectural upgrades alone because of his operation, so he followed the trend and said:
"There is no way, this It is determined by the level of hardware manufacturing. It is no less difficult to create a batch of 100% consistent components than to create a high-resolution and high-sampling rate ADC. Therefore, there is always some functional price to pay in order to compensate for distortion. In the final analysis, We still have to find a way to re-develop our own semiconductor industry, which is the right way. Just relying on speculation will definitely hit the ceiling early."
Everyone looked at each other when they heard this.
This is not a problem that their Electrical Engineering Department 14 can solve.
“It doesn’t matter, this kind of thing doesn’t happen overnight.”
Chang Haonan also understands that things must be done step by step.
Just like the previous layout of the civil aviation industry, if you want to influence this large-scale industry, the core is to find a starting point.
If you just say directly that I want to engage in the xx industry, there will definitely be no future.
“Let’s not think about things that far away. Since the principle works, then we should be able to get an engineering prototype for testing next?”
It can be seen that Guo Lin has already I am very hungry for the thing drawn by Chang Haonan——
When he first realized that high-standard components had to be used and that China was embargoed and could not import them, he thought that the project he had high hopes for was going to fail.
But now it is possible to use domestic components with relatively backward technical indicators to achieve the system indicators of high-end products.
Absolutely an unexpected surprise.
"Engineering prototypes must be made, and two must be made at the same time."
Chang Haonan glanced at the broken pod remains on the long table not far away:
"Make a compact version according to our own design, and then reproduce an American oversized pod in its original size. I want to see what's wrong with it..."
(End of this chapter )