Chapter 75 Radio Centipede
Friday.
Banxia hummed a song and spread out the drawings on the table.
The drawings provided by BG4MXH detailed the key points of modifying the GR3188 repeater and Icom725. Last night, BG4MXH patiently guided Banxia as if she was teaching a kindergarten kid Chinese pinyin, and she understood the function of each interface. He repeated a sentence three times, and repeated it three more times if she didn't understand. He appealed to her emotions, explained the reason to her, and persuaded her with earnest words. The girl studied very seriously and took down the English-Chinese dictionary that the teacher had left behind but had put aside, and she would flip through it whenever she had time.
It was a rare dry afternoon in late autumn. The windowsills were covered with bird droppings and the road was covered with golden fallen leaves.
The temperature was getting colder day by day. When the girl saw more and more squirrels in the community, she knew that another winter was coming. However, it did not snow in Nanjing in winter. The small animals had not had time to adapt to the climate change. They were still preparing for the winter. The thick winter fur that these small rodents had spent millions of years evolving would make them too hot to sleep in this winter.
It used to snow in Nanjing, but starting from a certain year, it stopped snowing.
"COR OUT... The Motorola receiver COR OUT of the repeater is connected to the PTT of the radio station."
"RX AUDIO, where is the RX AUDIO port? Here... it connects to the radio's MIC port."
“Finally, GND.”
Banxia was wearing a vest and shorts, with her hair tied into a ponytail. She sat cross-legged on a chair, with the table in front of her piled with electronic parts.
She pulled out the microphone of the Icom725 radio and curiously looked closely at it.
It was the first time that Banxia pulled out this thing. It was also an Icom hand microphone, the same brand as the radio. It was heavy, and the numbers on the buttons were blurry. It was unknown how long it had been used. It was probably as old as the radio. Banxia told the person there that they could hear the clanking of parts when the radio was moved.
The plug of the microphone is cylindrical. Generally speaking, this cylindrical plug is called an aviation plug. Its full name is "aviation plug". It is an eight-hole plug with a small hole in the center and other small holes evenly distributed in a circle. Its socket is in the lower left corner of the radio operation panel, corresponding to the plug. There are eight thin metal pins in the socket.
Each needle has different functions and uses. Banxia wants to connect the radio station and the relay together, and the first link must go through here.
A hand microphone is a microphone. People hold the hand microphone and speak, so usually the information is input into the radio station through the jack of the hand microphone.
This is the mouth of the radio station.
The repeater station's receiver will be plugged into the radio station's mouth.
The transmitter of the repeater station must be connected to the radio station later.
It's simply Radio 3P.
But Bai Zhen waved his hand: No, it's not Radio 3P, how can it be so promiscuous? The transmitter of the relay station is not responsible for output, it is the receiver.
Finally, a link is formed in which the receiver can transmit information to the radio station, and the radio station can transmit information to the transmitter.
So this is Radio Centipede!
In order to find out where the eight pins in the socket lead to, Bai Zhen and Wang Ning searched the entire Internet and found the instruction manual of the Icom725 amateur radio station.
"BG4MSR, look carefully at the microphone connector. The eight pins are numbered counterclockwise from 1 to 8. The middle pin is number 8. We need to use three connectors: PTT, MIC, and GND." Bai Yang explained carefully, "MIC is pin 1, PTT is pin 5, GND is pin 6 and 7. We need to use pin 7. Did you understand? OVER."
No one is talking in the channel.
"Did you hear that clearly? OVER."
No one is talking in the channel yet.
"Miss? BG4MSR? Are you there? Why aren't you talking? OVER."
Bai Yang kept urging Ban Xia, who had no choice but to put the microphone back in and said unhappily:
"Didn't you tell me to pull out my hands? How can I speak?"
·
·
·
Banxia turned on the soldering iron.
A soldering iron requires rosin. Banxia searched the entire computer city but couldn't find it. Bai Zhen then had an idea and asked her to rob a music store, and she found it.
Wang Ning reminded Banxia to be careful when using the soldering iron.
Don't hold your hands on the core.
Bai Zhen said there would be such a fool? His hand was on the iron core of the soldering iron?
Wang Ning asked why there were none left. Most of them were used as pens.
Banxia straightened the thin white wire on the relay station, then picked up a pair of scissors and, with a "click", cut off one end of the PCB board neatly.
The PCB board fell to the ground, and Banxia peeled off the white rubber covering of the wires, separating out three thin wires of red, black and yellow.
These three wires should be connected to the microphone jack on the radio.
The red line is COR OUT, corresponding to PTT.
The yellow line is RX AUDIO, corresponding to MIC.
The black wire is GND, corresponding to GND.
But there are metal needles in the socket of the 725 radio, and the wires are connected to the thin needles, with the needle tips facing each other, making it difficult to fix them together.
So Bai Zhen suggested that Banxia find some thin copper wire, and first wrap the thin copper wire around the pin in circles, making it into a thin and long spiral like a spring, to make sure that it can be put on the thin needle without falling off, and then pull out the spiral copper wire and solder it to the electric wire.
This is how you get a simple homemade plug.
"This needle is too thin, it's hard to insert." Banxia complained, "What should I do if my hands are shaking?"
“Do you have Parkinson’s?”
“What is Parkinson’s?”
"Parkinson's disease means hemiplegia and constant shaking."
"Really? That sounds interesting. I also want to have Parkinson's disease and keep shaking all the time."
Banxia soldered them all and connected the three wires of the repeater receiver to the corresponding pins of the radio's microphone socket, and half of the work was done.
Next is the other half.
The other half starts with the radio station’s butt.
It has two ports on its butt.
"Two sockets! ACC1 and ACC2!"
"Yes, there are two sockets on the 25-pin header. I told you that the one to use is the ACC1 socket! Look at the metal nameplate on the back of the radio. It says which one is the ACC1."
"right."
"Yes, the one on the right."
"This is a multi-hole interface. There are so many holes in this socket... one, two, three, four, five, six, seven, eight... eight small holes!"
In order to figure out the functions and uses of these eight small holes, Bai Zhen and Wang Ning searched the entire Internet again. It was really hard to find detailed information about this antique Icom725.
There are quite a lot of interfaces on the back of the Icom725 radio. The most eye-catching ones are the two circular ACC sockets in the middle. These are two multi-hole sockets. Each socket has eight spindle-shaped holes, which are spread out like a blooming chrysanthemum. It is just the opposite of the microphone socket. The microphone socket has needles, which are the input ports for information, while the ACC socket has holes, which are the output ports for data. The holes are easier to deal with and can be directly inserted with thin copper wires.
But how to insert and which ones to insert is the key.
"Hmm...the SQL OUT of the radio station is connected to the PTT of the repeater transmitter."
"EX SPEAKER connects to the transmitter's MIC."
“Finally, GND.”
Banxia still remembers BG4MXH’s advice.
She pulled out a thin white wire and straightened it - there is only one such connecting wire with PCB boards at both ends in a repeater station, and it is used to connect the transmitter and the receiver.
The connecting cable of the GR3188 relay itself had just been cut by Banxia.
At this moment, one end of the wire is plugged into the receiver and the other end is plugged into the microphone jack of Icom725.
So Banxia found another connecting wire from another relay of the same model, cut off one end of it neatly, and separated three thin wires of red, yellow and black from under the white rubber.
Solder a long copper wire to each of the three thin wires.
"Which hole is SQL OUT?"
"Hole No. 6."
Carefully insert the three copper wires into the butt of the radio.
Plug one end of this white connecting wire into the back of the radio and the other end into the transmitter of the relay.
At this point, Radio Centipede was completed.
This set of plans was successfully tested nine times by Wang Ning, Bai Zhen and others yesterday.
But it’s not over yet.
There is another important component - the antenna.
Wang Ning and Bai Zhen thought about the antenna issue for a long time. To be honest, antennas are basically purchased these days. The manufacturer sets the parameters for you and you can use it after installing it.
But in Banxia's era, there was no Taobao or JD.com, and online shopping was impossible. If you wanted to get an antenna, the easiest way was to make it yourself.
But Wang Ning and Bai Zhen hadn't made their own antennas for many years. It wasn't that they didn't have the ability, but there was already one. Why bother making it themselves? What's wrong with being a lazy dog? So they put their weapons into storage and let their horses go to the mountains.
"How do you make an antenna? Make it yourself?" Wang Ning asked.
"What else can we do?" Bai Zhen said, "Let's do it ourselves first to see the effect. If it works, we can teach her how to do it."
"What about impedance standing waves?" Wang Ning asked, "She probably can't measure it."
"Just make do with what you have. Anything more or less will do. They're all pretty much the same." Bai Zhen shook his head. "In the electromagnetic environment of her time, if she farted, the whole world would hear it."
Theoretically, all conductors can be antennas.
It's just that the effect is different.
So to make an antenna you can use materials anywhere, such as clothes drying rack, golden cudgel, Qiankun ring, tight hoop, purple gold bowl, nine-toothed rake, Fang Tian painted halberd, Green Dragon Crescent Blade. As long as you can get it, there is nothing that cannot be made into an antenna.
Wang Ning and Bai Zhen chose to use coaxial cable.
"Coaxial cable! Use coaxial cable. It's pretty easy to get. There are a lot of them in the city. It can be used for TV cables or Internet cables."
"It's best to find a 75-7, but a 75-5 is also fine!"
Coaxial cable is easier to find and more effective than Qinglong Yanyuedao. It is often used as an antenna feeder. In fact, it can also be used as an antenna itself. The structure of coaxial cable is simple. It has a two-layer structure with a metal wire core in the center and a fine metal mesh shielding layer outside the core wire. The space between the core wire and the shielding mesh is filled with insulating material, and the outermost layer is a rubber sheath.
Therefore, the cross-section of a coaxial cable is like a target, with a solid circle in the center and a series of rings on the outside.
To make a coaxial cable into an antenna, the most important thing is to remove the metal shielding layer.
The shielding layer is like a Faraday cage. The reason why the coaxial cable has stronger anti-interference ability than ordinary twisted pair cable is because of the existence of this shielding network. It can not only isolate external interference, but also prevent the electromagnetic waves generated inside the cable from radiating outward. Therefore, this layer of skin must be peeled off to allow the radio waves to spread out.
"144MHZ, how long should it last?" Wang Ning asked.
Bai Zhen stared at the black cables piled up on the floor, pondered for a few seconds, and did some quick calculations in his mind.
"About half a meter."
The two used a ruler to measure a length of 0.5 meters at the end of the coaxial cable, and then used a knife to cut a circle at the 0.5-meter position.
This was a massive circumcision, with the foreskin alone being half a meter long.
They peeled off the 0.5-meter-long slender foreskin, revealing the silver metal shielding mesh inside.
Wang Ning and Bai Zhen squatted on the floor, slowly rubbing the metal shielding mesh with their hands. With skillful techniques, they loosened the shielding mesh woven from soft metal wires, and then pulled it back little by little and put it over the rubber sheath of the coaxial cable like turning up the sleeves.
After installation, the simple entry-level 144MHZ antenna is basically completed.
This coaxial cable is both a feeder and an antenna. The stripped part is the antenna responsible for radiating radio waves, and the unstripped part is the feeder that transmits signals.
It's that simple.
Finally, Wang Ning used a standing wave meter to make fine adjustments.
The two conducted nine experiments with this antenna yesterday. The soft coaxial cable could not stand up by itself, so Wang Ning tied it to a wooden mop stick. He held up two mops and leaned out of the window, as if he was about to take off at any time, scaring the owners passing by in the community and calling the police.
In Nanjing in 2019, in the Meihua Villa community where power switches and electric vehicles are everywhere, these two seemingly simple whip antennas still stubbornly supported the verbal confrontation between Wang Ning and Bai Zhen.
"Old White, are you fucking done yet? My waist is about to break, and I'm telling you you have to compensate me for my medical expenses, at least five hundred bucks."
"I'll give it to you once you fly down. I promise to burn it for you, not a penny less."
"Go to hell, come up if you have the guts, come up and try."
"Come down if you can!"
"Come up here!"
"Come down!"
Banxia tied the finished coaxial cable antenna to a stick, and BG4MXH specifically reminded her to use an insulator.
There were two antennas in total, one for the transmitter and one for the receiver. The girl took great effort to extend them out of the attic skylight and place them on the roof.
144MHZ is the UV band, or more precisely the VHF band. Electromagnetic waves propagate within line of sight, so the higher the antenna is, the better.
Banxia asked how far it could reach?
Wang Ning shrugged. He couldn't say for sure.
In the conventional concept, UV waves are used for short-distance communication, but nothing is certain and there are exceptions to everything. As long as the conditions are right, the UV band can also communicate directly over hundreds of kilometers.
Bai Zhen said that Nanjing in the doomsday era would be deserted and the electromagnetic environment would be very, very quiet, so the signal-to-noise ratio of communications would be very good.
Wang Ning said that being in a world with only one person is indeed much easier, as you don’t even need to use a relay, because you’re the only one talking anyway.
That night, the girl charged the radio.
Baofeng UV9R waterproof version.
She went looking for waterproof handheld radios according to Bai Zhen and Wang Ning's instructions. Banxia found a total of 18 well-preserved waterproof handheld radios on Zhujiang Road. Products from Motorola, Yaesu, and other big brands were defeated one after another. In the end, only the Baofeng UV9R, a hundred-yuan magic phone with a very high stock, was still working properly.
Turn on the Icom725 radio.
Turn on the GR3188 analog relay.
Banxia took a deep breath. She had been busy on this for a whole week, and success or failure depended on this one move.
Gently turn the switch knob on the top of the radio and the LCD screen lights up.
On a night with a sky full of bright stars, the girl left her room, climbed up to the attic, sat on the roof, and told BG4MXH about the stars she saw.
(End of this chapter)
Continue read on readnovelmtl.com
