How antennas receive AM radio signals

[webberfolds]

The greater the amplitude of a given frequency of light hitting an antenna the greater the induced speed of electricity in the antenna? Reply in simple english please.

 

[vk6kro]

No, that applies to hitting golf balls, but not to antennas.

The speed of the wave in an antenna is comparable with the speed of light and it depends on the dimensions of the wire but not on the amplitude of the signal.

 

[webberfolds]

Then how does the energy from the amplitude of the light transmit onto the antenna? I appreciate the clear writing.

No, that applies to hitting golf balls, but not to antennas.

The speed of the wave in an antenna is comparable with the speed of light and it depends on the dimensions of the wire but not on the amplitude of the signal.

 

[vk6kro]

A stronger signal field strength results in a larger output signal from the antenna.

So, if the field strength is varying like a sinewave then a stronger field will produce a bigger sinewave output than a weaker one.

But the velocity of the wave in the antenna stays the same. Weak signals travel just as fast as strong ones in space and in an antenna.

 

[davenn]

Then how does the energy from the amplitude of the light transmit onto the antenna? I appreciate the clear writing.

the energy of light doesn't transfer onto an antenna
you have a little confusion I suspect

Tho an electromagnetic wave is composed of moving photons, those photons are are not visible light photons.
An electromagnetic E-M (radio wave) wave moving through space ( the air etc) will induce an electrical current into the metal wire/rod of the antenna ( or any other conductive surface it encounters). To get maximum efficiency of energy transfer (induced energy) the antenna length is cut so that it is resonant with the frequency of the radio wave.
that length can be determined by the formula wavelength = speed of light / frequency
an easy way to work that out for MHz of frequency is ...

300 / 100MHz = 3 metres (wavelength)
rarely are full wavelength antennas used more normally a halfwave one is used so you would divide that 3metres by 2 and end up with 1.5 metre for a halfwave antenna


Dave

 

[webberfolds]

If haven't noticed I don't know a lot about this science. What's meant by signal field strength? The magnetic field, electrical field, or both fields? A sine wave with a big amplitude does not always have a stronger magnetic field than a sine wave with a small amplitude? I appreciate the help a lot.

A stronger signal field strength results in a larger output signal from the antenna.

So, if the field strength is varying like a sinewave then a stronger field will produce a bigger sinewave output than a weaker one.

But the velocity of the wave in the antenna stays the same. Weak signals travel just as fast as strong ones in space and in an antenna.

 

[webberfolds]

Maybe transfer is the wrong word. When I wrote light I meant EMR, expecially radio waves. Why does the length of the antenna change the resonance of th antenna? So if the desired signal wavelength is 3 metres then what would be the best length for the antenna? I appreciate the help!

the energy of light doesn't transfer onto an antenna
you have a little confusion I suspect

Tho an electromagnetic wave is composed of moving photons, those photons are are not visible light photons.
An electromagnetic E-M (radio wave) wave moving through space ( the air etc) will induce an electrical current into the metal wire/rod of the antenna ( or any other conductive surface it encounters). To get maximum efficiency of energy transfer (induced energy) the antenna length is cut so that it is resonant with the frequency of the radio wave.
that length can be determined by the formula wavelength = speed of light / frequency
an easy way to work that out for MHz of frequency is ...

300 / 100MHz = 3 metres (wavelength)
rarely are full wavelength antennas used more normally a halfwave one is used so you would divide that 3metres by 2 and end up with 1.5 metre for a halfwave antenna


Dave

 

[davenn]

Maybe transfer is the wrong word. When I wrote light I meant EMR, expecially radio waves. Why does the length of the antenna change the resonance of th antenna? So if the desired signal wavelength is 3 metres then what would be the best length for the antenna? I appreciate the help!

Thats OK :) we all have to start some where
3 metres is the wavelength of a frequency of a 100 MHz ( in the middle of the FM broadcast band 88 - 108 MHz) radio wave.
I don't know what country you are in ? maybe you have the 27 MHz or 476MHz citizen bands
( also known as PRS ) lets, using the formula I gave you above, work out the wavelengths for each of those frequencies.

27MHz is at the high end of the High Frequency (HF) band
300 / 27MHz = 11.11 metres wavelength

476 MHz is around the middle of the Ultra High Frequency (UHF) band
300 / 476MHz = 0.630 metres = 63 cm wavelength

when the antenna is the same length as the wavelength of the radio wave its at its most resonant and will have the greatest amount of energy induced into it

To use a non radio wave analogy, but still the same principle, think of an opera singer who breaks a wine glass with her singing. The wine glass because of its size and construction will have its own resonant frequency. Now the singer can sing all sorts of musical notes at the glass, most won't have any effect as their frequency is too far from the resonant frequency of the glass. but as the singers musical tone approaches the resonant freq of the glass it will start to vibrate and if the amplitude ( loudness) of her singing plus producing the correct tone is just right it will cause the glass to vibrate so much it will shatter.
At that time the frequency of the tone ( note) being produced by the singer and the resonant frequency of the glass are the same and the glass absorb the maximum amount of energy.

does that help ?

cheers
Dave

 

[webberfolds]

Yes it does help me a lot and there's always more questions so answer if only feel like it. I don't understand how a sine wave passing by an antenna at a strange angle can induce a current that can be decoded..

Thats OK :) we all have to start some where
3 metres is the wavelength of a frequency of a 100 MHz ( in the middle of the FM broadcast band 88 - 108 MHz) radio wave.
I don't know what country you are in ? maybe you have the 27 MHz or 476MHz citizen bands
( also known as PRS ) lets, using the formula I gave you above, work out the wavelengths for each of those frequencies.

27MHz is at the high end of the High Frequency (HF) band
300 / 27MHz = 11.11 metres wavelength

476 MHz is around the middle of the Ultra High Frequency (UHF) band
300 / 476MHz = 0.630 metres = 63 cm wavelength

when the antenna is the same length as the wavelength of the radio wave its at its most resonant and will have the greatest amount of energy induced into it

To use a non radio wave analogy, but still the same principle, think of an opera singer who breaks a wine glass with her singing. The wine glass because of its size and construction will have its own resonant frequency. Now the singer can sing all sorts of musical notes at the glass, most won't have any effect as their frequency is too far from the resonant frequency of the glass. but as the singers musical tone approaches the resonant freq of the glass it will start to vibrate and if the amplitude ( loudness) of her singing plus producing the correct tone is just right it will cause the glass to vibrate so much it will shatter.
At that time the frequency of the tone ( note) being produced by the singer and the resonant frequency of the glass are the same and the glass absorb the maximum amount of energy.

does that help ?

cheers
Dave

 

[davenn]

Yes it does help me a lot and there's always more questions so answer if only feel like it. I don't understand how a sine wave passing by an antenna at a strange angle can induce a current that can be decoded..

OK, that leads us to the next stage. for a start don't get so wrapped up by this sine wave thing :)
An E-M field is made up of 2 separate fields and as you may guess they are an Electric field and a Magnetic field. These 2 fields are perpendicular to each other.

Thanks to the NZART for the graphic :)

OK back to antennas and angles and things...
You may have noticed as you look around that you see antennas orientated in one of normally two different polarisations, horizontal and vertical.
If the transmitting antenna is vertically polarised so will the receiving antenna. If the transmitting antenna was say, vertical and the receiving antenna horizontal, there would be a substantial reduction in the received signal strength because of the mismatch.

Above is a pic of a local radio tower site, you can see there are a mass of antennas on it, and this was only the top 1/3 of the tower
I have marked some of the antennas VP or HP to show you which ones are Vertically Polarised or Horizontally Polarised.
You can see that they are all pointing in various directions. All point to another antenna at the other end of the link which will have the same polarisation.

cheers
Dave

 

[webberfolds]

There's one that says VP and it seems to be HP to me. I notice that the VP antennas point up to the sky but in space there's no up. I'm learning so much but I don't know what I could do in return for helping me so much.

OK back to antennas and angles and things...
You may have noticed as you look around that you see antennas orientated in one of normally two different polarisations, horizontal and vertical.
If the transmitting antenna is vertically polarised so will the receiving antenna. If the transmitting antenna was say, vertical and the receiving antenna horizontal, there would be a substantial reduction in the received signal strength because of the mismatch.

 

[davenn]

There's one that says VP and it seems to be HP to me. I notice that the VP antennas point up to the sky but in space there's no up. I'm learning so much but I don't know what I could do in return for helping me so much.

which one are you referring to ? Maybe that vertical antenna on the left side of the mast ?

OK I will go through the antennas I have labelled ... from left to right...

1 -- a 9 element horizontally polarised Yagi
2 -- a vertically polarised colinear
3 -- a 9 element horizontally polarised Yagi ( one centre top)

then down the right hand side from top to bottom...

4 -- a vertically polarised dipole
5 -- a vertically polarised dipole
6 -- a 15 element vertically polarisd Yagi
7 -- 2 x horizontally polarised Yagis ( line is pointing to 2 antennas at the bottom)

Now I have introduced some new terms there for you to understand and learn

Yagi antenna ( NOTE the capital Y), the name comes from Prof. Yagi and his assistant Mr Uda, a pair of Japanese guys who invented the Yagi system many years ago .. do a google search on his name
A Yagi antenna consists of a number of elements from 2 to whatever, but ~ 35 is a practical limit depending in frequency.
eg ... a 10 element Yagi on say 10 MHz would be physically huge and have really huge wind loading ( wind resistance) 3 or 4 elements for frequencies around that area are more the norm.
but go to 100MHz and a 10 element Yagi is quite manageable
the Yagi's on that mast are mainly around the 400 to 500 MHz range and several others that can be seen lower down ( sort of a golden colour metal) they are maybe up ~ 1000 MHz give or take a bit. A 10 to 20 element Yagi on those frequencies is both relatively small and has high gain.
As you go higher in frequency above 1000MHz there becomes a trade off between size and gain and it becomes more practical to use a dish type antenna

will finish this post later I need to head away from home for a few hrs :)

Dave

 

[gnurf]

Yagi antenna ( NOTE the capital Y), the name comes from Mr Uda Yagi, a Japanese guy who invented the Yagi system many years ago .. do a google search on his name.

I did google Mr Uda Yagi and he seems to suffer from a severe case of split personality:

http://en.wikipedia.org/wiki/Shintaro_Uda
http://en.wikipedia.org/wiki/Hidetsugu_Yagi

 

[davenn]

ok to continue...
( I know we are a long way from your original question and I hope that's has been answered successfully :) ... I'm just passing on some radio antenna basics without getting into any serious maths explanations)

... As you go higher in frequency above 1000MHz there becomes a trade off between size and gain and it becomes more practical to use a dish type antenna
in this next pic there are several dish antennas...

a radome is simply an E-M transparent shield/cover over the front of a dish to protect it from animals and the weather.

basic dish ...

Using ray paths as you would with an optical mirror you can see the incoming ( received signal) or the outgoing, transmitted signal, being reflected off the parabolic surface of the dish coming to or from the antenna feedpoint. Dish antennas produce very hi gain as they focus the radio signal into a narrow beam

A basic Yagi antenna...

OK the pic above shows a simple 3 element Yagi ... the director element is at the front of the Yagi, then the driven element in the middle it is the active element and has the coax cable connected to it. Then at the back is the reflector element.
1 -- The director(s) element(s) are shorter than the driven element, ~ 5 - 10%.
2 -- The driven element is called a dipole and its length is a half-wavelength at the frequency its being used at, ( it is actually an electrical half wave-length, but we won't complicate the issue at the moment)
3 -- The reflector element is longer than the driven element, again ~ 5 - 10%

A dipole antenna on its own radiates reasonably evenly 360 degrees and is great if you want a wide coverage. But if you want to get a signal into a specific area then you use a Yagi with a reflector and one or more directors. This has the effect of confining the radio wave to a narrower beam so the signal can be aimed into a specific region.

OK let's see how you go digesting that and what questions it generates :)

cheers
Dave

 

[davenn]

I did google Mr Uda Yagi and he seems to suffer from a severe case of split personality:

http://en.wikipedia.org/wiki/Shintaro_Uda
http://en.wikipedia.org/wiki/Hidetsugu_Yagi

yeah my bad ... have edited my post

D

 

[webberfolds]

So it comes down to me trying to build an ornithopter (although it doesn't resemble a bird very much). I need it to be radio controlled and I want the radio control system inside it to be well defined for this ornithopter. I'm also interested in radio control for other reasons but I'm wondering how I could get the receiver inside to receive signals from long distances. Is it best to use an antenna or no antenna at all? Of course info on anything close to that will be appreciated.

... As you go higher in frequency above 1000MHz there becomes a trade off between size and gain and it becomes more practical to use a dish type antenna
OK let's see how you go digesting that and what questions it generates :)
cheers
Dave

 

[dlgoff]

I know we are a long way from your original question and I hope that's has been answered successfully :) ...

Ah. Now I can go a little off topic. :)

When I saw this,

Above is a pic of a local radio tower site, you can see there are a mass of antennas on it, and this was only the top 1/3 of the tower

I wanted to say, "I wish I owned the tower". Well maybe a lot off topic, but there's money to be made if you own one. The Department of Transportation here in Kansas has a information page as an example.

http://www.ksdot.org/burConsMain/Connections/Radio/LeasingTowerSpace.asp

Okay. Back to antennas.

 

[davenn]

Ah. Now I can go a little off topic. :)

When I saw this,

I wanted to say, "I wish I owned the tower". Well maybe a lot off topic, but there's money to be made if you own one. The Department of Transportation here in Kansas has a information page as an example.

http://www.ksdot.org/burConsMain/Connections/Radio/LeasingTowerSpace.asp

Okay. Back to antennas.

Hi Don
yeah costs for leasing space on towers and hi-rise buildings, here in Australia are very expensive. On a roof top, you usually pay by the sqr metre and you are limited to height of antenna etc. On a mast you pay, not only for the area but also position on the mast, eg. the higher up the higher the lease cost. And considering the ongoing need for more equip to be located on a finite number of tower sites, its really a license for the owners to "print money" haha

Dave

 

[davenn]

So it comes down to me trying to build an ornithopter (although it doesn't resemble a bird very much). I need it to be radio controlled and I want the radio control system inside it to be well defined for this ornithopter. I'm also interested in radio control for other reasons but I'm wondering how I could get the receiver inside to receive signals from long distances. Is it best to use an antenna or no antenna at all? Of course info on anything close to that will be appreciated.

OK, I had to look up ornithopter just to confirm we were both on the same page haha
There are many good radio control systems out there. All the best ones these days use 2.4 GHz and are digitally encoded to avoid multi system intereference. Any respectable model hobby shop will be able to guide you into something suitable. As for range, well out to around 1km would be an approximate maximum.
yes, of course you will need an antenna, and again the systems for sale come with an antenna suitable for the unit you are remote controlling :)

cheers
Dave

 

[webberfolds]

Actually I meant that I want to aim towards learning about that, any attempt to help me will be appreciated but it would help me most to know about how I can make the radio control. Learning about antennas is very good.

Of course info on anything close to that will be appreciated.

 

[webberfolds]

I'm sort of a perfectionist and I want to make a simple but very effective remote control system that's specifically designed for the ornithopter. I have other reasons for wanting to know about it but I am very interested in radio control.

OK, I had to look up ornithopter just to confirm we were both on the same page haha
There are many good radio control systems out there. All the best ones these days use 2.4 GHz and are digitally encoded to avoid multi system intereference. Any respectable model hobby shop will be able to guide you into something suitable. As for range, well out to around 1km would be an approximate maximum.
yes, of course you will need an antenna, and again the systems for sale come with an antenna suitable for the unit you are remote controlling :)

cheers
Dave

 

[davenn]

Actually I meant that I want to aim towards learning about that, any attempt to help me will be appreciated but it would help me most to know about how I can make the radio control. Learning about antennas is very good.

No one makes radio control systems themselves, everyone just buys the receiver modules and controllers. The electronics is much too complex for the average hobbiest to get into.
its a big enough job just buying the controllers and installing the module and servos into your model.

Dave

 

[davenn]

I'm sort of a perfectionist and I want to make a simple but very effective remote control system that's specifically designed for the ornithopter. I have other reasons for wanting to know about it but I am very interested in radio control.

read my last post that I was typing and posting as you posted this

Dave

 

[webberfolds]

Maybe there's a simple and effective way, I don't mind if the controller is crude but I have difficulty being satisfied with a good radio system. I don't think of myself as much of a hobbiest (although I do do origami) but more of a want-to-be pioneer. I don't want to waste your time. What can I do to help and I don't want to feel like I'm taking advantage.

No one makes radio control systems themselves, everyone just buys the receiver modules and controllers. The electronics is much too complex for the average hobbiest to get into.
its a big enough job just buying the controllers and installing the module and servos into your model.

Dave

 

[davenn]

Maybe there's a simple and effective way, I don't mind if the controller is crude but I have difficulty being satisfied with a good radio system. I don't think of myself as much of a hobbiest (although I do do origami) but more of a want-to-be pioneer.

and what electronics design and construction skills do you have ?

D

 

[webberfolds]

Hardly any, but I can learn, I haven't been studying for very long. I know it may seem foolish but I sort of want it to be done right and if I want it done right I may have to do it in a way that satisfies me.

and what electronics design and construction skills do you have ?

D

 

[davenn]

Hardly any, but I can learn.

then building isn't an option for you, you are not going to learn in 5 days, 5 weeks or 5 months the skills needed to do this sort of complex work.
sorry if that sounds harsh, its a reality you need to understand.
So often on forums like this we have people coming on wanting to build something and they have none to little electronics abilities, they think its just a simple thing of soldering a few wires and components to a circuit board and presto a project... it just doesn't work that way

Your only choice is to buy a ready working system and do the mechanical work needed to control the unit. that alone will have you doing lots of head scratching :)

If you have a genuine desire to learn electronics, that's awesome, there are plenty of good book for teaching theory and have practical guides. But learn to crawl before you try to walk or run.
I don't know what country you are in, maybe there are electronics hobby stores like jaycar, radio shack etc etc that you can buy kitsets to build up and start to learn the basics. learn how to solder, how to use a multimeter, how to fault find in the kit you build but doesn't work.
As I said its not something you are going to learn in any short term period of time.
I have been playing with electronics since I was ~ 8 years old and am now well over 50 yrs old, and I will be the first to admit that I don't know it all. There are many days I go to work and come across different faults in equip I have to repair that really test my abilities.

cheers
Dave

 

[webberfolds]

I am not planning on building it for a long time and I do have a genuine interest in it. I would like to know if AM or FM is better for this and what sort of antenna is best for this. I do consider myself a dreamer and I need to think about reality too, I agree.

then building isn't an option for you, you are not going to learn in 5 days, 5 weeks or 5 months the skills needed to do this sort of complex work.
If you have a genuine desire to learn electronics, that's awesome, there are plenty of good book for teaching theory and have practical guides.

 

[davenn]

I am not planning on building it for a long time and I do have a genuine interest in it.

OK then enrole in a local technical institute and do a diploma or similar in electronics :)
You will learn a good amount from books etc but nothing beats actual classroom interaction with other students and lecturer

D

 

[webberfolds]

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!

OK then enrole in a local technical institute and do a diploma or similar in electronics :)
You will learn a good amount from books etc but nothing beats actual classroom interaction with other students and lecturer

D

 

[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.