Trucks use two air lines to the brakes to do the same thing. 18 wheeler trucks use a RED and a BLUE brake line. Just as with trains, a spring holds the brakes on. When air is applied to the red air hose, the brakes are released. The brake pedal on the truck is an air valve that allows some air into the blue line that applies the brakes. it works by counter balancing brake diaphragm near the wheels. The brake diaphragm has two chambers. When both chambers have no pressure the springs apply the brakes. When the chamber for the red line has 100psi of pressure on it, the force of the spring is overcome and the brakes release. When air from the blue line fills the service brake side of the chamber it subracts from the force. So if you have 100psi in the red side and 50psi in the blue side, you have half braking force. if you have 100psi on the red side and 75psi on the blue side you have 3/4 braking force. and if you have 100psi on both sides, you have 100% braking force.
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Why do trucks use two air lines rather one one like trains? because it allows for more precise control!
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How do ham radio operators talk around the world? The simple answer is by bouncing radio waves off a layer in the atmosphere called the ionosphere. If radio waves didn't bounce off the ionosphere then we would not be able to talk to people beyond our visible horizon.
It is just like light bending in a prism. Different wavelengths (frequencies) of light and radio waves will bend more or less when they enter a substance with a different density than air.
It is just like light bending in a prism. Different wavelengths (frequencies) of light and radio waves will bend more or less when they enter a substance with a different density than air.
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So how do we talk to the international space station? Or even get a radio signal to reach a satellite? In the first post today, there is a diagram that shows that radio waves don't turn sharply... they curve. As we use higher and higher frequencies, the radio waves have more and more energy in them and aren't made to bend as much in the ionosphere. at around 55mhz radiowaves don't bend enough to come back down to the surface... they zig zag through the ionosphere. Once we get to 150mhz, radio waves shoot straight through into space. So if we use frequencies higher than 55mhz, we can reach space!
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When the sun strikes the ionosphere, it makes it thicker and closer to the surface of the earth. This means that radio waves will bounce closer during the day and further at night. This is why you hear far away AM radio stations at night but not during the day.
So how would a ham radio operator reach a person in another country? They would calculate the distance to that person using a great circle map. Let's imagine the person is 3000 miles away. The 11meter (29mhz) ham band will bounce 1500 miles at night. So the radio wave would bounce off the ionosphere 750 miles away, hit the earth at 1500 miles, bounce a 2nd time off the ionosphere at 2250 miles and finally hit the earth at 3000miles away. Or the ham operator could switch to 20meter (14mhz) band and only bounce once at 3000 miles. The lower frequency only bouncing once would allow the radio to work using less power.
So how would a ham radio operator reach a person in another country? They would calculate the distance to that person using a great circle map. Let's imagine the person is 3000 miles away. The 11meter (29mhz) ham band will bounce 1500 miles at night. So the radio wave would bounce off the ionosphere 750 miles away, hit the earth at 1500 miles, bounce a 2nd time off the ionosphere at 2250 miles and finally hit the earth at 3000miles away. Or the ham operator could switch to 20meter (14mhz) band and only bounce once at 3000 miles. The lower frequency only bouncing once would allow the radio to work using less power.
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I am a ham radio operator and I have talked to the international space station and to the astronauts on MIR in the 1990s. In the late 90's Kenwood made one of the first digital cameras and it had a very neat feature. It could send slow scan video over a voice channel on radio. It took about 36 seconds to transmit one picture. It was slow but it worked. The astronauts on MIR enjoyed talking to hams on earth and sending pictures to us. We could talk to them for about 8 minutes at a time. They sent me pictures like this.
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Off The Grid Kid
I am a ham radio operator and I have talked to the international space station and to the astronauts on MIR in the 1990s. In the late 90's Kenwood made one of the first digital cameras and it had a very neat feature. It could send slow scan video over a…
I should have posted this with the space station pictures the other day.... here's how those analog images "sounded" over the radio. https://www.youtube.com/watch?v=tuyEwI9fJGk
YouTube
SSTV Video From The International Space Station
SSTV video in Robot 36 format received in NJ from the International Space Station on Sunday October 12, 2008. This image was received on a frequency of 145.800 MHz, decoded using QSSTV software, and shows a graphic of the ISS above the Earth.
This video…
This video…
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Electricity basics. Electricity we use in our houses and vehicles is AC or DC. AC is "alternating current". It goes positive and then negative and positive again 50 or 60 times a second depending if you are in the US & Cananda or the rest of the world. Most countries use 50hz but here in North America we use 60hz. With DC (direct current) the current is simply on all the time.
We use DC on things that are close to us. Your car, a tractor's electrical system, a laptop computer. These things simply need to work. DC is usually limited to 5v, 12v, 24v or 48v. Thomas Edison's original DC system used 120vdc but that is not at all common these days.
AC on the other hand is used for when we need to either run larger power powerful devices or transmit power over a long distance. That distance might be a few hundred feet across your yard or a hundred miles.
Why do we use AC? Why not just use DC? In order to transmit power over longer distances we need to boost the voltage to very high levels. Transformers can easily boost voltage up and bring it back down. So we often boost voltage up to 115,000v, 230,000v or even 500,000v to move it hundreds of milles. But we cannot use 500,000v in the walls of our homes, that would be dangerous. So there is a transformer in a green box or on a pole in your front yard that will convert the power company transmission voltage down to 120vac or 240vac used in your house.
And the last step in using electricity is converting from 120vac or 240vac to a very low DC voltage such as 5vdc to run your phone charger.
We use DC on things that are close to us. Your car, a tractor's electrical system, a laptop computer. These things simply need to work. DC is usually limited to 5v, 12v, 24v or 48v. Thomas Edison's original DC system used 120vdc but that is not at all common these days.
AC on the other hand is used for when we need to either run larger power powerful devices or transmit power over a long distance. That distance might be a few hundred feet across your yard or a hundred miles.
Why do we use AC? Why not just use DC? In order to transmit power over longer distances we need to boost the voltage to very high levels. Transformers can easily boost voltage up and bring it back down. So we often boost voltage up to 115,000v, 230,000v or even 500,000v to move it hundreds of milles. But we cannot use 500,000v in the walls of our homes, that would be dangerous. So there is a transformer in a green box or on a pole in your front yard that will convert the power company transmission voltage down to 120vac or 240vac used in your house.
And the last step in using electricity is converting from 120vac or 240vac to a very low DC voltage such as 5vdc to run your phone charger.
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How to measure angles.
We use a protractor to measure angles. there are even protractors that measure a full circle. If you took a circle and divided it up into 360 equal slices, each slice would be 1degree. If you want to go half way around a circle, that would be 180 degrees.
But did you know that it doesn't stop at 1 degree? If you take a degree and divide it into 60 slices that is called a minute or sometimes an Minute of Angle. And if you take that minute and divide it into 60 slices, you'll have seconds.
The cool thing about using 360 degrees or 60 degrees is that the numbers are very easy to divide by 2,4,5, 6,12, 15, 20, 30, 60. So if makes it very easy to make multisided shapes (like a pentagon or hexagon) or even gears.
We use a protractor to measure angles. there are even protractors that measure a full circle. If you took a circle and divided it up into 360 equal slices, each slice would be 1degree. If you want to go half way around a circle, that would be 180 degrees.
But did you know that it doesn't stop at 1 degree? If you take a degree and divide it into 60 slices that is called a minute or sometimes an Minute of Angle. And if you take that minute and divide it into 60 slices, you'll have seconds.
The cool thing about using 360 degrees or 60 degrees is that the numbers are very easy to divide by 2,4,5, 6,12, 15, 20, 30, 60. So if makes it very easy to make multisided shapes (like a pentagon or hexagon) or even gears.
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In the english system, we call one minute of angle a MOA. In the world of guns, we find that by coincidence, 1 MOA at 100 yards (300 feet) is about 1 inch.
If you were to shoot a target that was 100yards away and the bullet did not hit where you were aiming, you would want to adjust the scope on the rifle.
We way we do this is measure how far the bullet is high or low / left or right and adjust the elevation or windage on our scope. There is a knob you can turn and it will most likely say one click = 1/4 MOA.
So we find that the bullet hit 1" too low at 100 yards. That is 1 MOA. Since we need the point of impact to move up 1", we turn the elevation knob 4 clicks in the UP direction. If the bullet struck 2" to the left, we would move the windage 8 clicks RIGHT because we need to move the point of impact to the right.
If you were to shoot a target that was 100yards away and the bullet did not hit where you were aiming, you would want to adjust the scope on the rifle.
We way we do this is measure how far the bullet is high or low / left or right and adjust the elevation or windage on our scope. There is a knob you can turn and it will most likely say one click = 1/4 MOA.
So we find that the bullet hit 1" too low at 100 yards. That is 1 MOA. Since we need the point of impact to move up 1", we turn the elevation knob 4 clicks in the UP direction. If the bullet struck 2" to the left, we would move the windage 8 clicks RIGHT because we need to move the point of impact to the right.
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