Sitting in the east wing, Du Yande quickly looked at the telegraph magic device that Wen Desi mentioned earlier, and they were placed on a table, which was different from the single magic weapon he had seen before, it was actually composed of several dark green devices.

There are a lot of black buttons on these devices of different sizes, and some of them look like dashboards in the cab of excavators, which Du Yande can't read at all, but some of these devices are old, as if they have been used for decades, because the dark green paint on the equipment has fallen off in several places.

Du Yande was staring at these things, and heard Chief Hu next to him laughing, "Hey, good guy, the telegraph machine was actually transformed like this, no wonder Lao Huang said that he was a fool." ”

At present, this kind of radio transmitter is an outdated equipment, and except for a small number of second-line combat units that are still in use in the troops, all others have abandoned it and replaced it with more advanced communication equipment, that is, most of the ones in use have been replaced with computer keyboards.

"Chief Du, Fang Cai Lao Wen said that he used this magic device to receive a call from Chief Huang, is this also a walkie-talkie, but it is much farther than the walkie-talkie we used before." Du Yande remembered that the walkie-talkie used on the island can only transmit at most 10 miles away, and the sound is very blurry if it is far away, basically it is not clear to hear, and now Dongluo Island is also 200 miles away from Fuzhou Prefecture, and it seems that the chief's magic weapon has been "upgraded" again.

"This is a radio transmitter, but it is different from the walkie-talkie we use now, although they are all radio signals."

Different walkie-talkies have different bands and different ranges of objects, usually ordinary walkie-talkies are civilian, such as taxis, HAM radio amateurs. The shortwave is mostly a professional HAM, that is, international and inter-regional, which is used by special civil aviation, military, and Hainan Airlines. Now the intercom used on Dongluo Island is only civilian, that is, the ordinary model, which can only provide fans with daily short-distance use.

Flipping open a notebook on the table with his hand, Hu Guang saw that a USB cable was plugged into this notebook, and then this line **** in an obviously handmade device, which was sprayed with red paint with the words "signal converter", and at the same time, a data cable also came out at the other end of the "signal converter", but it was connected to the radio transmitter, which was originally the place to connect the heavy electric key.

Hu Guang casually typed a few passwords on the keyboard of the notebook to see if he could try to open the computer, and said to Du Yande on the other hand, "Because the transmission of radio carrier signals is different according to their transmission frequency." It is first divided into ground waves and sky waves, of which ground waves are divided into long waves and medium waves; As for the sky wave, it is divided into medium and short waves; Then there is the penetrating wave, which has three types, there are direct waves, ultrashort waves, and microwaves. ”

Du Yande continued, "Oh, we heard Chief Huang say these words in physics class. ”

"Do you know the difference?" Hu Guang couldn't have imagined that the physics class given to them by Huangshi would teach such in-depth content.

Du Yande shook his head and replied, "No, Chief Huang only told us about these terms, but he didn't say what these terms mean. ”

"In this case, I'll just give you some popular science." Hu Guangzhi said, it is estimated that the physics lesson that Brother Huang gave them is actually still a nature course, and now it is better to talk to him when he has time, it is purely idle to talk to him.

"Hehe, thank you Chief Du."

"Ha Lu Ha, no. By the way, Chief Huang should have told you that the earth we are on is round, right? ”

Du Yande nodded and replied, "I've already said it." ”

When everyone saw Huang Shi holding a big round ball and a big box in his hand into the classroom, they were all wondering what kind of objects these two were.

Then in class, I heard Chief Huang say, "This is the planet we live on, the earth under our feet, and this is a globe made by our people in the upper realm according to the geographical map of this earth." ”

"Globe?!" Most of the people present in the class did not understand, only three or two people had heard that Zhang Heng of the Han Dynasty had invented the "Wind and Earth Motion Instrument" and the "Water Transport Armillary Sphere", so they all looked at the round ball on the table with suspicious eyes.

Huang Shi turned the globe around, found the yellow and green areas on the earth, and then pointed his finger on it, and said to them, "This is the Ming Dynasty." ”

The people below hesitated but did not respond, so Huang Shi beckoned to them, "You come up and get closer, so that you can see clearly." ”

When everyone gathered around and saw the position of Huang Shi's finger clearly, he only let out a soft "oh".

Huang Shi continued his efforts, turned the globe half a circle, pointed to it and said, "This is the American continent I told you about the other day. ”

This time, everyone's voice was a little louder, because it was true that a few days ago, when Chief Huang was holding a geography class, he once brought a big and big "Imperial Map", on which there was a "American Continent", and the chief also said that the land above is vast and sparsely populated, and it is really rich in resources, and there are Jinshan and Jinhe on it, but there are only a few countries, called "Aztec", "Inca Empire" and other small countries, the number of people is also very small, and the total is less than half of the Ming Dynasty.

However, in the past, everyone thought that the earth was flat, and people's heads were covered with a piece of heaven like an iron pot, which was what the ancients called "the sky is round", and the Ming Dynasty was in the center of this piece of heaven and earth. And according to Chief Huang's statement, although I don't believe that the chief will lie to them, it seems that there is something wrong.

Finally, a quick-witted warrior asked, "Chief, we all live on top of this ball, that's fine, but not all the people of the 'Inca Empire' you talked about two days ago are going to live with their heads down, and they're not all going to fall." ”

Hearing someone say this, everyone woke up to the fact that something was wrong here, so they discussed, "Yes, these people from small countries are really pitiful......

Before he could figure out how to explain this, Huangshi heard another warrior say, "Nonsense, I think if they fall so easily, then there will be no one in these countries for a long time, where can there be the 'Inca Empire' and 'Aztec' that the chief said!" ”

Huang Shi couldn't help but nodded, and said in his heart, it seems that there are still smart people who know how to think.

But before he could give the warrior a compliment, he heard someone else ask, "Then tell me, why don't they fall so easily." ”

So Yellowstone was silent, wanting to see what the warrior would do to explain the problem.

The warrior didn't actually think of an answer, but he saw that everyone else was waiting for him to answer, and Chief Huang was also looking at him with a smile, so he replied with some apprehension, "I thought, that's the only one who has practiced a kung fu of walking with a big head down......

Speaking of the latter, he felt that he was right, and his voice became louder, "Just like the bats in those caves, they don't sleep like that. ”

……

Hu Guang didn't know that there was such a story in Lu Dao, and when he was preparing to explain, he dipped his fingers in some tea and drew a picture of Du Yande on the table.

"You see, there is an ionosphere around the outside of our earth, and this ionosphere is like an eggshell, and it can reflect some short radio waves, such as this telegraph transmitter, which uses short waves, so you can see that it can be emitted from our transmitter, and then reflected back to the ground by this layer of eggshells, and then reflected back from the ground, so that a few reflections back and forth can transmit these radio waves to a long distance, like from Dongluo Island to Fuzhou here is relatively short, if longer, It can also be launched to the other side of the earth. ”

"However, the density of the ionosphere will often change with the weather, and the density is higher at night, and if you send a telegram at this time, then the transmission distance will be relatively long. However, this portable shortwave radio station is at close range, so it is a few hundred kilometers away at most. ”

"Oh, chief, what about Nakaha?"

"The medium wave is transmitted around the surface of the earth, it is not greatly affected by the weather, and the transmission is more stable than the short wave, but because of the ground absorption and obstacles, it can only be transmitted in close distance, and it is generally used to transmit the broadcast signal of the station."

"Broadcast signals. Chief Hu, I remember that Chief Huang said that in addition to playing DVDs with DVD players, TV sets can also receive TV signals, are they the same thing? Du Yande remembered a recent incident.

"No, the TV signal is meant to carry images and sound, while the broadcast signal is just to transmit sound. Therefore, the TV signal should be transmitted by microwave, which is shorter than the wavelength of short wave, because its frequency is high enough, and the amount of information it carries is very large, but the transmission distance is closer, and if you don't use cable TV, you can generally only receive a very close TV station, so now above us, the big TV stations are relayed through satellites. ”

At this moment, Du Yande was in a fog, and there were microwaves under the short waves, and he couldn't imagine what the wavelength was, anyway, it was like listening to the sky.

"As for the long wave, it is a meter wave, which is transmitted close to the ground and the sea surface, and the transmission signal of the meter wave is very stable, but the ground absorbs it too much, so it needs a lot of transmitting power." Hu Guang still remembers that long-wave was originally used for long-range broadcasting, but now except for Russia, which still uses it, other countries have basically eliminated its application, except for some military scientific research projects.

"Also, the TV signal we just talked about is a kind of microwave, which is a penetrating direct wave like ultra-short wave......"