How antennas receive AM radio signals

[davenn]

I edited some of my other posts, there's some questions on them. What can I do in return for helping me in the previous posts?I have serious anxiety around people but that's another story. I got to go to bed now, good night!

You are never wasting my time as long as you are willing to learn :)
When I was much younger in both age and electronics experience, long before the internet was even dreamed of, I got to know a couple of good electronics technicians really well.
one was my electronics tutor at the tech college, a chinese guy with great patience and could tell things in an understandable way. The other guy was a radio technician for a large government department, I spend many saturday mornings at his place and some times his working day workshop. Not only did he fill in holes in my general electronics knowledge, he also taught me a lot about RF (radio) electronics as it was his field of expertise.

Having mentors is a wonderful thing and something I suggest you see if you can find local to where you live. Someone that you can take non-working projects to and ask for help and let them guide you through the steps of fault dinding etc.
A good mentor won't just sit there and hand you all the answers on a silver platter, as so many expect these days, but will give you hints and tips of things for you to try so you can with a little help work out the problem pretty much on your own.

Thats what we try and do on these forums when people come asking questions
we want to know you have at least done a little research on your own. Google is a wonderful thing, probably 90% of questions asked on these forums could have been answered if the questioner had just posted their question into google.
Where we can help is when the person has done that on google, but there is something in the answer they don't understand, then at least then they can come here and a good specific question :)

Its all part of the fun of learning

cheers
Dave

 

[webberfolds]

I have tried google for these questions but I often find FAQ that don't help me much, or answers in unclear or confusing english. I get questions like why the sky is blue and I already know some basic reasons for that. Part of me wants to accept good enough and part of me doesn't, I know I have a lot to learn about accepting good enough. I want to feel like I'm working on the project the right way but my thinking process has to evolve so I can finish it. I try to think of easy ways to get AM radio control on my own but it would only work if electricity acted a certain way and it likely doesn't. If know a any good books or similar stuff about how radio signals are picked up by an antenna or how how electrical current moves the wires I'd love to know. anyway thanks for all the help! If want I can send origami as gift for helping me or something because I feel like I'm taking too much. I have one question sadly, why do the antennas have to be VP or HP? In space there's no up or down in a way. The main reason I started writing about the ornithopter was not because I wasn't interested in the antenna info but because I felt that I had to get down to the most needed info for me because I didn't want to be annoying and I didn't want to take too much of your time. If helping me with this was a paid job then it would be different. That's what it comes down to, it's not as if learning much from me.

You are never wasting my time as long as you are willing to learn :)
When I was much younger in both age and electronics experience, long before the internet was even dreamed of, I got to know a couple of good electronics technicians really well.
one was my electronics tutor at the tech college, a chinese guy with great patience and could tell things in an understandable way. The other guy was a radio technician for a large government department, I spend many saturday mornings at his place and some times his working day workshop. Not only did he fill in holes in my general electronics knowledge, he also taught me a lot about RF (radio) electronics as it was his field of expertise.

Having mentors is a wonderful thing and something I suggest you see if you can find local to where you live. Someone that you can take non-working projects to and ask for help and let them guide you through the steps of fault dinding etc.
A good mentor won't just sit there and hand you all the answers on a silver platter, as so many expect these days, but will give you hints and tips of things for you to try so you can with a little help work out the problem pretty much on your own.

Thats what we try and do on these forums when people come asking questions
we want to know you have at least done a little research on your own. Google is a wonderful thing, probably 90% of questions asked on these forums could have been answered if the questioner had just posted their question into google.
Where we can help is when the person has done that on google, but there is something in the answer they don't understand, then at least then they can come here and a good specific question :)

Its all part of the fun of learning

cheers
Dave

 

[LegendLength]

Personally I would recommend building the aircraft first using off the shelf components. During that process you'll come to understand the internals of the radio transmitter, receiver, control boards etc..

You will find there are areas that are very, very complex and really require a PHD to understand well. A prime example is aerial design. Sure, you can build an antenna yourself and it will work ok. But if you want to do any kind of optimization or increase the signal strength you quickly run into a lot of complexity.

I have actually studied ornithopters in the past and can tell you it's all possible with parts ordered over the internet. Everything is basically the same as an RC plane except for a small control board that makes the wings (servos) flap.

If you try to continue down the path you're on (building every component yourself) you'll be blindly fumbling through. If you build a simple ornithopter first using standard components then it will help you see what the real issues are and you can then focus specifically on those, and then build your own stuff to solve those issues.

I would start with programming an existing control board (for wing flapping). That will surely keep you busy for a good 6 months.

Finally I would recommend posting in some of the RC forums if you are after specific information such as range or real-world issues.

 

[webberfolds]

It does seem like a good idea but I don't want to pay a lot money for it, I heard shipping costed over $100 for one and it wasn't even that big, too much! The thing is, are there so many components inside it that I can learn from? Often there's only two wings that go up and down when flying (actually maybe my partly-designed ornithopter should not be called one because it has atleast 4 wings and birds almost always have 2 wings.) If there's only 2 basic wing movements (up and down) how complicated can the RC system be? I want to learn a lot from it and I don't want to waste money expecially and time. Thanks for the help! (Sorry I didn't reply earlier, I left my computer somewhere.) Why does it take atleast 6 months? I'm having trouble finding the right ornithopter though.

Personally I would recommend building the aircraft first using off the shelf components.

 

[sophiecentaur]

If you want a radio control system for a plane you would be advised to buy one. This will be lighter and better than you can design and build yourself unless you really get into the subject. Also you have to use a permitted frequency band at a permitted transmitter power.

 

[webberfolds]

It's an ornithopter I'm trying to build, anyway I get the point, I'm waiting for 2 ornithopters that I want to build that are gifts for me. They're rubber band powered and not RC but I'll see what I can learn from them and will be beautiful to look at. I would like to know of a good inexpensive RC ornithopter kit that I can buy too. Thanks for the post!

If you want a radio control system for a plane you would be advised to buy one.

 

[LegendLength]

Webber, just have a glance at some of the ornithopter forums and it should give you a good idea of their evolution and issues they've run into along the way.

I'm also a do-it-yourself type of guy but in this case it seems like you'll spend a lot more time and money trying to build it yourself without using a working reference design.

My 6 month comment was if you wanted to try and do some custom coding for something like the flight controller (wing flapper board). It's just an example area you can get into if you want to buy off-the-shelf components but still do your own engineering.

I don't know current costs for them but it surely couldn't be more than a couple of hundred bucks delivered for an entry level kit. I mean you can get 9 channel transmitters these days for 30 bucks from places like hobbyking. Motors, servos, batteries are all cheap.

 

[webberfolds]

It's good to know that I can buy 9 channel transmitters for 30 bucks, I really don't mind much if the remote controller is crude. So it would be able to transmit 9 different frequencies? Wouldn't some frequencies be a bit better than others? I'll look at the ornithopter forums soon, thanks for the posts !

Webber, just have a glance at some of the ornithopter forums and it should give you a good idea of their evolution and issues they've run into along the way.

I'm also a do-it-yourself type of guy but in this case it seems like you'll spend a lot more time and money trying to build it yourself without using a working reference design.

My 6 month comment was if you wanted to try and do some custom coding for something like the flight controller (wing flapper board). It's just an example area you can get into if you want to buy off-the-shelf components but still do your own engineering.

I don't know current costs for them but it surely couldn't be more than a couple of hundred bucks delivered for an entry level kit. I mean you can get 9 channel transmitters these days for 30 bucks from places like hobbyking. Motors, servos, batteries are all cheap.

 

[webberfolds]

Say there's an EM wave moving parallel to the length of a straight wire connected to a circuit. Say the EM wave is strong/close enough to induce current in the wire. Would the current move in the direction the EM wave is moving, or the opposite way? How would the current change from time to time?

 

[sophiecentaur]

No signal will be induced by an em wave traveling parallel to a wire.

 

[webberfolds]

Then what angle(s) would? I'm so confused about how antennas receive signals, thanks for the post!

No signal will be induced by an em wave traveling parallel to a wire.

 

[davenn]

I'm trying to find out more about how electrical signals move in wires. I'd also like to know the best angle for a RW of a given polarity to go by a straight conducting wire to induce the most current in it. Do know any good resources for that? I'm asking for resources because it seems time-consuming to teach me individually.

I really wish you would stop asking the same questions in 2 different threads
it makes it really difficult for people to follow the discussion

I have already given you an answer in your other thread


Dave

 

[webberfolds]

Copy and paste error, I meant to move the comment that had nothing to do with the other thread and move it to this thread and not to post the identical one there, I got to go watch a movie, sorry, so bye for now.

I really wish you would stop asking the same questions in 2 different threads
it makes it really difficult for people to follow the discussion

I have already given you an answer in your other thread


Dave

 

[davenn]

I don't see it in the other thread, sorry.

This one
you were asking similar stuff.

its better to keep your questions to your threads,
now you are even confusing me ;)

this was my response to learning more and a reference...

try the ARRL Radio Handbook
it gives a very good background to radio transmission and reception including antenna theory

cheers
Dave

 

[webberfolds]

Please read my previous post on this thread when feel like it, I deleted my posts on the other thread that were off-topic. Also, when I wrote "it seems time-consuming to teach me individually" I was considering your time, not mine, I don't want any misunderstandings about that, anyway, good night.

This one
you were asking similar stuff.

its better to keep your questions to your threads,
now you are even confusing me ;)

this was my response to learning more and a reference...



cheers
Dave

 

[sophiecentaur]

Then what angle(s) would? I'm so confused about how antennas receive signals, thanks for the post!

Diagrams of EM waves are all over the Web. They show the direction of propagation of a simple, (linearly polarised) wave and the two fields (Electric and Magnetic) are at right angles to that direction (it's a transverse wave). Those 'wiggles' are not what it looks like - they are vectors, representing the magnitude and directions of the fields at points along a line in the direction of interest. In fact the wavefronts are planes (or the surfaces of very large spheres, spreading out from the source).
To pick up the maximum signal, you orientate a straight wire parallel with the E field (i.e. at right angles to a line joining the transmitter to you). The transmitting antenna will also, for a linear polarised wave) probably consist of one or more straight wires, also at right angles to the direction in which the 'beam' is directed.

 

[webberfolds]

I'm trying to understand what is meant by this, what field interacts with the antenna if the straight wire is parallel with the Electric field? Only reply if want to.

To pick up the maximum signal, you orientate a straight wire parallel with the E field (i.e. at right angles to a line joining the transmitter to you).

 

[davenn]

I'm trying to understand what is meant by this, what field interacts with the antenna if the straight wire is parallel with the Electric field? Only reply if want to.

The electric field does. When the electric field is parallel to the antenna polarisation, then the maximum power is transferred to the antenna. If they are at 90 deg to each other then there will be a minimum of energy transferred.
As I said in this or the other thread... in practice there is some 25 - 30 dB difference in signal strength between correct polarisation between E field and antenna compared to 90 deg out of polarisation between the two.


Dave

 

[webberfolds]

How can the E field induce the current if the E field is parallel to the antenna? The E field would have to 'touch' the antenna to induce current, I must have read it wrong. So if the polarisation of the wave is VP and the antenna is VP then maximum power is transferred, is that what mean? I did read the post about dB difference but I was a bit confused what was meant by it, it's a good bit of info though, thanks.

The electric field does. When the electric field is parallel to the antenna polarisation, then the maximum power is transferred to the antenna. If they are at 90 deg to each other then there will be a minimum of energy transferred.
As I said in this or the other thread... in practice there is some 25 - 30 dB difference in signal strength between correct polarisation between E field and antenna compared to 90 deg out of polarisation between the two.


Dave

 

[sophiecentaur]

Charges will flow in the direction of an electric field.

 

[webberfolds]

That makes me think, is the E field of an EM wave positive or negatively charged or something else?

Charges will flow in the direction of an electric field.

 

[davenn]

How can the E field induce the current if the E field is parallel to the antenna? The E field would have to 'touch' the antenna to induce current, I must have read it wrong. .

hold your arms out in front of you they are parallel to each other
you left arm is the antenna, your right arm is the E-field wavefront,
as your right arm (e-field ) moves from right to left it encounters the antenna
at that time it induces a current into the antenna

Dave

 

[webberfolds]

So if the antenna is VP, the line the EM wave is going is best when it is parallel with the ground (ignoring the idea that space-time is curved)? Getting very close to making me understand !

hold your arms out in front of you they are parallel to each other
you left arm is the antenna, your right arm is the E-field wavefront,
as your right arm (e-field ) moves from right to left it encounters the antenna
at that time it induces a current into the antenna

Dave

 

[davenn]

So if the antenna is VP, the line the EM wave is going is best when it is parallel with the ground? Getting very close to making me understand !

no

if the antenna is vertically polarised the e-field will also need to be vertically polarised (perpendicular/90deg to the ground) to induce maximum signal into the antenna

think of a pebble thrown into the pond and the waves you see propagating out are the E-field. In this case they are parallel to the ground. IF you have a vertical stick ( the antenna) pushed into the water and into the bottom of the pond then it is vertically polarised but the waves are horizontal and there would be minimum interaction between the stick ( antenna) and the waves, as the waves passed by the stick.

now you could lie the stick horizontal in 2 significant ways ...

1) the stick lies parallel to the oncoming wavefront . that's going to produce maximum interaction between the stick and the passing wavefront. or ...

2) the stick could be end on to the wavefront...ie... the incoming wave hits the end of the stick ... this also produces a minimum interaction between the wavefront and the stick ( antenna)

OK got it that time ? :)

Im running out of different ways to describe it ;)

Dave

 

[webberfolds]

The antenna is HP in that situation and the E field seems to be VP but that does not seem good.

1) the stick lies parallel to the oncoming wavefront . that's going to produce maximum interaction between the stick and the passing wavefront.
Dave

 

[davenn]

The antenna is HP in that situation and the E field seems to be VP but that does not seem good.

yes the stick is HP and I said that the waves were horizontal

read again what I wrote


D

 

[webberfolds]

I think I get it! I'm not a fast learner by the way.

yes the stick is HP and I said that the waves were horizontal

read again what I wrote


D

 

[davenn]

have a look at this was the only decent wave pic I could find

OK its the polarity of the wave front that determines whether its horizontal or vertical
in water we can only have horizontal as in the pic above

The wavefront is the length wise measurement of the wave as depicted by the blue line from lower left to upper right

The height of the wave is NOT the polarity of the wave ... and that may be where you are tripping over ... the height of the wave is its amplitude

So you can see I have 2 poles/sticks ( antennas) one is vertical ( the left one) the other is horizontal and is parallel to the wave front


Dave

 

[sophiecentaur]

How's the EM wave HP? Is it because it's heading in a horizontal direction? That doesn't sound right.

The polarisation and the direction of propagation are two entirely different issues. The E field is at right angles to the direction of propagation. There is a slight problem here in actually defining the direction of polarisation in terms of H and V. If you have a 'vertically polarised' transmitting antenna then the E field will, indeed be vertical for the wave that is traveling horizontally. If an HP wave is traveling in a horizontal direction, the E field is pointing at right angles to the direction of propagation; that is still horizontal. For a nominally VP wave that is traveling upwards (remember, it is spreading in all directions) at an angle of 45°, the E field, being at right angles to this direction, is not actually vertical but tilted back at 45°. If you fire any linearly polarised signal vertically, however the antenna is orientated, the E field will be horizontal (all lines at right angles to vertical are horizontal). One of the reasons for using circular polarisation for satellite transmissions is that there is no problem distinguishing between clockwise and anticlockwise and there can be no misunderstanding.

That makes me think, is the E field of an EM wave positive or negatively charged or something else?[QUOTE/]
The question doesn't make sense, I'm afraid. Field is Field and Charge is Charge. A field doesn't 'have a charge' a field can exist between around a charged object or between two charged objects. To have a field, there must have been two opposite charges somewhere to cause it. In the case of an EM wave, the alternating fields were caused by some movement or changes in a set of charges somewhere (e.g. an antenna or a decaying atom).

I suggest you do a bit more reading a bit less one-to-one questioning now. There is loads of information out there.

 

[webberfolds]

Yes, I suddently got it before that post but that post helped to clarify my understanding. I really shouldn't have asked that question about if if the E field was positively or negatively charged. The main reason is that I could probably have found out a lot about it on google and I worded it really incorrectly. Sorry. Anyway thanks for all the help. (No need to reply to this post.)

The polarisation and the direction of propagation are two entirely different issues. The E field is at right angles to the direction of propagation. There is a slight problem here in actually defining the direction of polarisation in terms of H and V. If you have a 'vertically polarised' transmitting antenna then the E field will, indeed be vertical for the wave that is traveling horizontally. If an HP wave is traveling in a horizontal direction, the E field is pointing at right angles to the direction of propagation; that is still horizontal. For a nominally VP wave that is traveling upwards (remember, it is spreading in all directions) at an angle of 45°, the E field, being at right angles to this direction, is not actually vertical but tilted back at 45°. If you fire any linearly polarised signal vertically, however the antenna is orientated, the E field will be horizontal (all lines at right angles to vertical are horizontal). One of the reasons for using circular polarisation for satellite transmissions is that there is no problem distinguishing between clockwise and anticlockwise and there can be no misunderstanding.

I suggest you do a bit more reading a bit less one-to-one questioning now. There is loads of information out there.