# Radio Frequency Transmitter Project

Discussion in 'General Electronics Discussion' started by Jay.E.Eh.S, Jun 23, 2014.

1. ### Jay.E.Eh.S

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Apr 11, 2014
Hi, first of all, I would like to mentioned to you all that I'm only a first year student of mechatronic engineering and so I have only basic and limited knowledge regarding electronics but this is not gonna be my excuse of not to improve myself.

This is my personal project which is related to RF. Here's the schematic I get (print-screen) from a video on Youtube.

Here's my doubts and questions :
1) What's that 5 turns mean and for what? Inductor? And why the antenna is connected to the second coil?

2) As what I know, NPN transistor acts as a switch, but in this circuit, I THINK it's not just only as a switch? In other words, can anyone explain to me briefly on how this circuit work? I have learned impedance, phase shift and phase angle and so on, so I have only a blur image in my mind regarding this circuit.

3) I know that air trimmer is to adjust the frequency of the RF wave. But I just wanna know any idea or ways to change it to digital display so that I can know what frequency of wave is the circuit transmitting (instead of using another device to check its frequency) ?

Your generous help is very much appreciated

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2. ### Harald KappModeratorModerator

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2,654
Nov 17, 2011
1) 5 turns means an inductor with 5 turns. The symbol does not show a core, so the inductor is just 5 turns of wire wound to an air coil. the antenna taps into the coil, where exactly is not really clear from the schematic. You'll probably find more detail in the video you mentioned.

2) A transistoir can be used as a switch, but not exclusively. In this circuit it is operated as an analog amplifier to create the oscillations. This circuit ia a Colpitts type oscillator.

3) This is an analog circuit. There's no easy way to add a digital readout to this circuit. For knowing the frequency, add a dial to the variable capacitor and calibrate it using a frequency meter.
If you want a digital readout, you'd have to add a frequency meter permanently to the circuit.

3. ### Jay.E.Eh.S

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Apr 11, 2014
1) The video shows just connect the antenna to the second coil will do. No reason were told.

2) Thanks for the link! So now I know it's Colpitts type oscillator

3) I see. Any simple frequency meter schematic with digital display I can build and combine with this RF circuit?

4. ### davennModerator

13,837
1,952
Sep 5, 2009
frequency counters are not overly simple
maybe there are some cheaper ones on eBay

do an eBay search for frequency counter ... as something useful you would want something that can go to at least ~ 500 MHz

cheers
Dave

5. ### Ehsan

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Jun 12, 2014
If you like these stuffs I suggest you change your major from mechatronics to electrical engineering or telecommunication or something related.

To fully understand that circuit you need to wait until you get to the third year of yout college. Any explanation will make you more baffled.

Frankly speaking, even if you manage to build that circuit, you won't learn anything except SOLDERING.

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Apr 11, 2014
Okay. thanks

7. ### Jay.E.Eh.S

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Apr 11, 2014
Haha. But I like mechanical stuff too and I feel like mechanical knowledge plays an important role in making a complete robotic stuff, that's why I choose mechatronic Yea maybe you're right I may have only understand soldering but I do believe if I do more research and keep seeking answers for my questions, more or less, no loss but instead, I gained.

8. ### BR-549

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Jun 20, 2014
The antenna tap on L1 is an tuning adjustment. Depending on the length of the antenna and the ground associated with it, adjust tap up or down for max pwr out and gives you efficiently. I am quite sure the circuit operation can be explained to you. It would not be brief. You should have no problem learning electronics on your own. It will cost you \$30. Go to Amazon and buy "Electronic Communication" by Shrader......second edition only. One word of warning. In 1970 I was educated as a mechanical engineer. A friend of mine gave me this book and I never went back. Good Luck.

9. ### Jay.E.Eh.S

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Apr 11, 2014
Thanks BR-549. Will go and get the book soon.