After buying everything, Duan Yun took the bus back to the factory.

There was no one at home, so after Duan Yun put the package of components under the bed, he took out the multimeter and enameled wire he had just bought and prepared to modify the radio at home.

Modifying this 'primitive' radio was a piece of cake for Duan Yun.

Found a used scrap book from his sister's bedside, and Duan Yun used a pencil to draw a circuit diagram on it according to the components of the radio.

Speaking of which, since Duan Yun was in college, he basically used CAD software, but the technology of hand-drawn circuit diagrams has not fallen behind at all.

The short-wave reception sensitivity of repairing and modifying the radio is not a high technology, but Duan Yun has another idea.

For the average electrician, there are two ways to improve the shortwave sensitivity of the radio:

The first is to increase the working current of the frequency conversion tube. However, increasing the working current is very limited, and this method not only does not improve the selectivity, but also makes the noise of the inverter tube larger.

The second is to connect the 465KHz series resonant element in parallel between the short-band oscillation coil tap and the ground. Although this method can improve the selectivity of the radio, there is often no position on the circuit board for the post-additive components.

However, these two methods have limited improvement in the sensitivity of the radio, and the effect is not obvious.

Duan Yun only thought for a moment before thinking of a feasible modification plan.

He first removed the three IF transformers from the radio, and when he opened the case, the internal structure of the enameled wire was revealed.

After Duan Yun quickly calculated the number of turns required to replace the enameled wire, he replaced the original 0.8 wire diameter enameled wire with the newly purchased 1.0 wire diameter enameled wire.

It's a delicate job, but fortunately, Duan Yun is a very hands-on person, and he was the leader of his class when he first came into contact with radio internships in college.

It took Duan Yun half an hour to re-wrap the coil of the transformer, and according to his own ideas, he added several capacitors and resistors to the electric soldering iron in the input and output circuits of this radio.

The bulk resistors that Duan Yun bought were not marked, so they could only be tested one by one, and then the components that could be used were picked out.

After more than ten minutes, the radio that Duan Yun had modified was finally completed.

Compared with the electrician who can generally modify the radio in these years, Duan Yun's level is obviously much higher, the general electrician can only amplify the short-wave signal by increasing the working current of the frequency converter, but it will also increase the noise, resulting in the listening effect is still very poor, and the radio modified by Duan Yun not only greatly improves the sensitivity of short-wave reception, but also greatly improves the selectivity, and has an obvious advantage, that is, there is no noise at the station, and this improvement is the reason why the parallel resistance used by Duan Yun is smaller. The selection of stations has also been made easier, and the previously weak and floating radio signals have become easier to receive, and the phenomenon of mixed stations has been greatly improved.

After a brief test, Duan Yun was very satisfied with the results of his modification, and immediately packed up the multimeter and soldering iron and put them back under the bed.

"Brother, you didn't go to work today?"

Just as Duan Yun was about to close the back cover of the radio, with the sound of a clicking door lock, his sister Duan Fang had already appeared at the door with a schoolbag.

"The workshop is not alive today. Duan Yun prevaricated casually, and then said to Duan Fang with a smile: "It's just right to come, I fixed the radio for you, how about you try the signal?"

"Do you really know how to fix the radio?" Duan Fang was skeptical when he heard this, but he still took the radio from his brother.

"Let's go. When Duan Fang just turned on the radio, he didn't hear the familiar noise, and his brows suddenly furrowed.

But soon, something surprising happened to her.

The radio's medium-wave signal was noticeably clearer than before, and there was no noise in the search for channels, and channels that had not been heard at all before.

What surprised Duan Fang the most was that for the first time, she used short wave to listen to a lot of foreign language channels clearly during the day, and the clarity of the signal made her smack!

Among Duan Fang's classmates, there are many very wealthy dual-income children, and the small radios they use are all new on the market, but none of them can receive so many and so clear foreign radio signals during the day!

"How?" Duan Yun asked with a smile.

"Brother, how did you do it?" Duan Fang's little face was full of joy, and he couldn't put down the little radio in his arms, and said to Duan Yun, "You went up to the city today to repair it?"

"I said that your brother and I modified it myself. Duan Yun pursed his lips, and then said: "Remember what you told me before, bring a radio when you go to cram school on Saturdays and Sundays, help me and your classmates advertise, modify a machine for five yuan, and if the business is good, buy you something delicious!"

"Five yuan!" Duan Fang was taken aback when he heard this, and then said, "This ...... That's a bit too expensive, isn't it?"

"It's not expensive, and the materials for the modification cost a lot?" Duan Yun smiled, and then said: "You are as poor as other people'......s families are like us, they can spend more than a hundred to buy the best radio on the market, and it is not a matter to spend an extra five yuan, so it's okay, every time you get me a business, I will share your one dollar?

Duan Yun knew that his sister was born with sharp teeth and could speak well, as long as this girl was really willing to work hard to promote in school, there would definitely be a business, so he simply used the dividends to 'buy' her, anyway, this is not a speculative crime, and it will not affect her study and life.

"One is only one dollar?" Duan Fang's eyes suddenly lit up when he heard this.

The biggest amount of pocket money Duan Fang got from childhood to adulthood was when she was in elementary school and organized a spring outing on June 1st, when she clearly remembered that her mother gave her two yuan, which still included the money for a lunch.

Now that there is a dollar for a single business, this is definitely a huge income that Duan Fang can't even imagine!

"Your brother and I always count!" Duan Yun raised his eyebrows.

"Cheng!" Duan Fang said very simply.

"After making money, let's eat meat every day!"

"You still eat meat every day, brag about you! Our factory, the factory director's family dare not say that he has meat to eat every day. Duan Fang said this, but she was very happy in her heart, and said, "I'll go cook first, brother, you wait." ”

After speaking, Duan Fang shook two small braids and prepared to wash vegetables and cook.

My mother worked overtime at the sewing club at noon and didn't come back, and there were only two brothers and sisters for lunch.

My sister's cooking skills are not good, and she doesn't know how to cook much, in fact, there are not many dishes to cook at home.

Many girls in this era basically learned to cook very early, which is also a compulsory subject before marriage.

Looking at the food that basically didn't have any oil flowers, Duan Yun, who had been served by his fiancée Xiaozao in his previous life, was a little difficult to swallow, but now that the family has this condition, with his mother's salary alone, it is already good to be able to maintain food and clothing.

This also made Duan Yun secretly determined to make money as soon as possible, and to make a lot of money!