Frequency for Beginners

[Cham]

Hello, I'm new to the forum and somewhat new to electronics. My experience right now is that I have a year-long high school digital electronics course under my belt. I'm a senior now, looking to possibly minor in electrical engineering and do a lot of hobby work on electronics. My knowledge is of basic circuit logic, resistance, capacitors, that kind of thing. I'm especially interested in frequency though, and have read a bit about oscillators. If anyone has good resources on things having to do with frequency and breadboard experiments involving it, I'd love to have them on this thread. Also, I picked up a $10 pair of walkie talkies, took them apart, and did not find an oscillator on the circuit board. It has a transformer, inductor, antenna, various transistors, various resistors, and various capacitors, as well as the speaker/input, battery pack, PTT button and on/off switch. Does anyone know how this walkie talkie transmits? Sorry that this is such a long post. I'm new to the forums and wasn't sure how much I should include, so I just included everything. I'd appreciate any help on this. I'm eager to work with this stuff, but I'm just hitting a roadblock here.

 

[BobK]

There is probably a crystal to set the frequency and the oscillator will consist of a transistor, the crystal and some capacitors and resistors.

A picture of the PC board would be helpful.

Bob

 

[(*steve*)]

essentially, the transmitter creates a rapidly changing electromagnetic field that can be detected by a receiver. Frequency is essentially the rate at which that field is changing.

 

[Cham]

Thanks much, Bob and Steve. So I imagine the antenna determines the radius of the electromagnetic field, right? And Bob, for some reason I can't upload pictures of the circuit board to this thread directly, so I put them on postimage.org. Here are thumbnails to them. Hopefully all of the components are clear enough in the pictures. If you need anything more clear, I can focus in on any areas of interest for you.

 

[davenn]

yeah there is a uploading problem
I have contacted the board owner to look into it


Dave

 

[duke37]

"So I imagine the antenna determines the radius of the electromagnetic field,"

Take a bucket, half fill it with water to make it heavier then pump it up and down in a pond. You will see ripples diverging from the bucket. The wavelength is the distance between the ripples and will be smaller the faster you pump.

A radio transmitter uses a version of light so everything is much faster, I do not know what you mean by radius of the electromagnetic field.

 

[Cham]

This makes sense. What I meant by radius was how far the ripples would go before dissipating. I know the walkie talkie has a range. Is that range determined by the antenna or are there other factors?

 

[Minder]

Transmission power (watts).
Many years ago, there was a radio station in the UK called Rugby Radio that transmitted on very low frequencies at high power, the signal was supposedly receivable 6ft under water anywhere in the world.!!
High frequency transmissions are often line-of-site, to get world wide reception before satellites, the radio signal was bounced off of the ionosphere layers.
http://www.fountainmagazine.com/Issue/detail/The-Importance-of-Ionosphere-in-Radio-Communication
M.

 

[(*steve*)]

In essence, the waves will continue forever, getting weaker and weaker as they spread out further and further (think of the ripples in a pond and how they get smaller and smaller as they move outward)

Eventually the ripples are so small that they are indistinguishable from the background -- but they're still there.

The main thing an antenna does is to cause the radio signal to be pointed where it will do the most good. In the case of a radio station, for example, you want most of the signal to go parallel with the earths surface and to minimize the amount that uselessly goes straight up or down.

 

[Cham]

Wow, this is some very cool stuff. So if I were theoretically to increase the wattage of the walkie talkie, I would increase its range. Now, with pointing the signal, why do walkie talkie antennae point straight up if they want to minimize unnecessary ups and downs?

 

[Minder]

The signal radiates tangentially from the upright antenna.
And for maximum reception a receiver antenna should be the same disposition.
Antennas are tuned for the frequency (wave length) they operate on.
M.

 

[Cham]

Oh, right! That'd make sense because the signal acts as a field, not a ray. I don't know why I was thinking of it as a ray. I read up that you can use an inductor/capacitor with a transistor to make an LC oscillator, which would explain why I couldn't find a crystal oscillator on the board. Could you explain the LC oscillator? I found some things about it online, but it seems very abstract and I'm having troubles visualizing it practically.

 

[Minder]

First study L/C resonance (tuned) circuits, both series and parallel,at the tuned (resonant) frequency the inductive reactance is equal to the capacitive reactance , if you hit a parallel tuned circuit with a pulse(energy) it will 'ring' at its resonant frequency, just as striking a bell causes the resonant (audible) frequency.
M.,

 

[Cham]

Okay, I'll look into that next. Thanks much for all the help!