Refected Power

I guess in a basic way of looking at it, yes that is just about it.

In both cases you are trying to get the line matched so that phase angles match at the source of the signal.

In cases of antennas that have transmission lines over a quarter wave its best to match them at the source of the problem. At least that is my opinion. With 50/60Hz systems, the chance of you being that far way from your feeders are kind of nil? I mean we are talking like 4+ M feet here :)

Jamie

"Cursitor Doom" napisa? w wiadomo?ci news:n3er25$1or$ snipped-for-privacy@dont-email.me...

The electrical supply lines are the closed circuits. There no reflections. The reflections are possible in the open circuit. The radio mast is the open end of such circuit.

The end of the mast radiate. The rest is in Steinmetz book: The radiation is described here:

You can see that the radiation (electric waves) transports negative charge. The charge is rythmically expelled from the end of the transmitting antenna. If the all is perfectly tuned than no reflection at all. The all charge jump off in the air. In this book you find everything about the antennas. S*

I think that is the key difference I was looking for; many thanks for that.

Yes, point taken. :-)

That's silly. How do spacecraft antennas work then?

Cheers

Phil Hobbs

"Reflected power" is an odd concept for local power lines, to be sure.

As a point of interest (to us, it matters deeply to some), though, if you start at Bonneville Dam on the Oregon-Washington border and travel 1/4 wave of 60Hz south, you'll end up somewhere in between San Francisco and Los Angeles. Since the impedance of high-frequency transmission lines is in excess of 100 ohms (I don't know how much more, I'm eyeballing it), and the impedance of the load at the substation is probably less than 10 ohms, this can be an ISSUE. It's part of the reason that long-range power transmission is DC.

That's a bit unfair, Phil. Clearly English isn't his first language but the meaning is clear enough.

Quoting Steinmetz on how antennas work is like quoting Aristotle on mechanics, I'm afraid. They don't eject any charge whatsoever unless you hit them hard enough to generate corona discharge. It's entirely a field effect.

Cheers

Phil Hobbs

Maybe But can think of more practical reasons why they use HV DC.

Jamie

There's a lot of good reasons -- I'm pretty sure that the biggest two are losses in AC transmission lines that aren't there with DC, and the ability to intertie two grids running off of different clocks.

One big reason AIUI is that corona losses depend mostly on peak voltage, so you can transmit nearly twice the power on a DC line.

Cheers

Phil Hobbs

The all is here: "The secret lay principally in the direct current application in a small time interval. " From:

The radio was the top secret in XIX and XX century. Now the all is online. But not in the textbooks. It will be after 250 years like the Copernicus. Now is 125 years after Tesla discovery.

But in the XX from time to time was published the true information:

S*

Tesla was a crackpot and when he grew old he was nuts.

w.

Do not you know that (for example): "The necessity or utility of the earth connection has been sometimes ques- tioned, but in my opinion no practical system of wireless telegraphy exists where the instruments are not connected to earth. By "connected to earth" I do not necessarily mean an ordinary metallic connection as used for ordinary wire telegraphs. The earth wire may have a condenser in series with it, or it may be con- nected to what is really equivalent, a capacity area placed close to the surface of the ground (Fig. 4)". From:

But Marconi is like Aristotele. So look at this: "The use of the term ground (or earth) is so common in electrical and electronics applications that circuits in portable electronic devices such as cell phones and media players as well as circuits in vehicles may be spoken of as having a "ground" connection without any actual connection to the Earth, despite "common" being a more appropriate term for such a connection. This is usually a large conductor attached to one side of the power supply (such as the "ground plane" on a printed circuit board) " From:

Radio was the top secret. Now you know that it is the device to pump the electrons from the earth to air. But the electrons are pumped in the PORTIONS. S*

So you have the possibilities to check if light transports electrons. For example through the transparent insulator. It will be the Edison experiment who covered the bulb with the metal foil and had the source of DC floving to the earth. S*

After Tesla and Steinmetz was Richardson: "It has been suspected for a long time that electrons-could be pulled out of metals without the co-operation of gases by sufficiently strong electric fields. These currents are carried by electrons and they may be quite large. From:

Before the corona discharge is the field electron emission. Without the sound and visual atractions. In the pulse mode the the emission is 150 times stronger. S*

Richardson is talking about how vacuum tubes work, not antennas. His talk is on thermionic emission from heated cathodes. Nice try.

Everybody knows you can turn up the field enough to cause field emission. Just about all the electron microscopes I've ever used have been based on field emission. (There was one old Hitachi that still had a heater in it, but that was long ago.) That's entirely beside the point here.

But if that were true, (1) radio waves wouldn't travel at the speed of light, (2) spacecraft would charge up positive until they were unable to transmit any more, (3) you wouldn't be able to transmit anything whatsoever until the fields got large enough to cause field emission, and (4) antennas with rounded corners on their elements would be far less efficient than sharp-cornered ones.

None of which is observed. Your cell phone does not cause field emission next to your ear, for a start. (You'd know if it did, believe me.)

You can also build interferometers with radio waves, and beam antennas, and other things that depend on the field picture of antennas. None of which is true of field-emitted electrons.

Antennas work because charges radiate when you accelerate them. All the fanciness is in figuring out how to make all this (electromagnetic) radiation come out in phase in the direction you want it.

If you're actually interested in the subject, you can get an international-edition copy of Balanis's antenna book for about $20 on amazon.co.uk. It's a good read if you feel like making an effort to understand.

Cheers

Phil Hobbs

I'm not talking about a ground connection. Anyone with a cell phone or transistor radio knows that you don't necessarily need one.

I'm talking about emitting electrons till the spacecraft charges up so far positive that no more can escape. Voyager 1 has been transmitting just fine for what, 40 years?

Cheers

Phil Hobbs

If you know about the field emission you should know that it works in the two ways. The conductor gain or expel. The metal body of the spacecraft gain electrons from the space.

Before sending the spacecraft with the transmitter NASA was sending the model with the electron gun. It was the same like checking of the ground. How much electrons can be obtain from the metal body in the long time. S*

You're cracked.

Cheers

Phil Hobbs