Some questions regarding frequency stemmed from coax cables

[caphair]

So I started pondering about how coax cables work and now I'm stumped about a few things pertaining to radio waves/frequency.

In a coax cable there is a center conductor, insulating dielectric, braided metal shielding, and an outer insulator. My question, does the metal shielding also transmit a signal? Like is it part of the transmission?

My mind keeps going back to + and - as in a dc circuit where you need both for a current to flow, but in radio waves do you need a ground reference? Does the metal shielding act as a "ground" per say or merely there to protect interference occurring to the center conductor?

I also have a hard time distinguishing impedance and resistance. Like when something mentions the impedance of a speaker cable for example.

Thanks in advance!

[goontron]

Re: Some questions regarding frequency stemmed from coax cables

think of it like a mains ground and a live feed. you get current flow, but not through neutral. much like how NEMA code before the 90s had ground on a dryer acting as an active conductor. Radio waves work because there is potential between them and the ground. you dont need you radio grounder persay, you need differing potentials.

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

Hmm so does that mean an antenna for example has two connections? For ground and the signal or just one? Idk why I'm getting so confused about this lol

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

That would be a balanced line. https://en.wikipedia.org/wiki/Balanced_line

BTW, I believe goontron meant ground not neutral.

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

So is the shielded part of a coaxial cable to suppress noise to ground or is it the signal return line?

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

It is both.

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

Ok thanks. I guess my confusion stemmed from how some antennas require a ground and some don't.

Do RFs require a return line?

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

It's difficult to explain and it depends on what you mean by RFs. Over the air or transmission lines?

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

Yes like radio/tv waves. My understanding is they're a mixture of electrical and magnetic waves that an antenna picks up. But then how does the antenna connect to the circuit? Is it same as say how a transformer is connected?

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

Radio wave propagation is very a complex subject. I'm sure there is reading online that can explain much of it much better than I could or would want to try

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

I tried some and only caused more confusion lol.

What I'm mostly curious about is how the antenna is physically connected in a circuit. Does it have to ends or one?

[SteveNielsen]

Re: Some questions regarding frequency stemmed from coax cables

Either, it depends on the antenna type and receiver.

[Longbow]

Re: Some questions regarding frequency stemmed from coax cables

This is a large subject, but fortunately it is covered in painful detail on many engineering web sites. Do not be mislead by the word "shielding". For the time being the word conductor will do. Yes, both the inner and outer conductor of a piece of coax carry the signal from one place to another.

To get a more specific answer, you must first specify what type of signal, along with details about your source, load, and characteristic impedance of the coax.

Keep in mind that at radio frequencies, the outer conductor can act like 2 separate conductors. In other words, you have the center conductor, the inside of the outer conductor, and the outside of the outer conductor. Coaxial cable provides a solution to certain RF transmission problems. It is not often used to carry d.c. from one place to another.

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

My confusion stems from when I picture electronics I refer to two points (+/-)

So I reference that in terms of radio waves and how an antenna can only have one connection starts to confuse me

[stj]

Re: Some questions regarding frequency stemmed from coax cables

http://www.ac6v.com/antprojects.htm#theory

[goontron]

Re: Some questions regarding frequency stemmed from coax cables

That would be a balanced line. https://en.wikipedia.org/wiki/Balanced_line

BTW, I believe goontron meant ground not neutral.

Yay, i even confused myself....

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

Anyone know the name of the older antennas like in RC cars that can be stretched out and then pushed back in. Are they considered dipoles?

[stj]

Re: Some questions regarding frequency stemmed from coax cables

telescopic.

dipoles are 2 poles with a joiner - like a "H" shape

[R_J]

Re: Some questions regarding frequency stemmed from coax cables

Its a monopole telescopic antenna, The coax cable is a transmission line to get the signal from the amp to the antenna and not be radiated along the way. most monopole antennas have a ground plane ie 2-way radios either use the cars body as a ground plane or if it was a base station antenna it would have ground plane radiators mounted horzontally to the vertical antenna.

[caphair]

Re: Some questions regarding frequency stemmed from coax cables

Its a monopole telescopic antenna, The coax cable is a transmission line to get the signal from the amp to the antenna and not be radiated along the way. most monopole antennas have a ground plane ie 2-way radios either use the cars body as a ground plane or if it was a base station antenna it would have ground plane radiators mounted horzontally to the vertical antenna.

Do the telescopic antennas have ground planes as well? They just look like metal rides bolted down. What exactly are the ground planes used for? Could radio waves be detected without them?