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Old 14th November 2007, 01:31 AM   (permalink)
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What about the 72mhz transmitters? I just need to know how to make a simple transmitter + receiver which i can then plant into an rc vehicle. This is jsut to learn and its not for long. I am buying a real transmitter system but i just want to learn how it works and how to build one and modify to do what i want to do.

Any help would be appreciated.
Thanks.
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Old 14th November 2007, 01:59 AM   (permalink)
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A simple transmitter and receiver are junk.
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Old 28th November 2007, 09:33 AM   (permalink)
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Thanks audioguru, your transmitter will make a good project...
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Old 29th December 2007, 01:42 AM   (permalink)
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Audioguru,
Do you have a coilless 27 Hhz AM transmitter schematic, I mean with X-tal. My experience, I have that schematic that was very simple but I lost it. My current project is building a 27 Hmz walkie talkie. Can you help me?
Thank's.

harries
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Old 29th December 2007, 01:57 AM   (permalink)
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Every transmitter that I have ever seen except one, uses coils and capacitors in a tuned circuit to reduce harmonics that cause interference at other frequencies. The one that doesn't use a coil operates from the 9th harmonic of a 10.7MHz ceramic filter. It is very low power so its other harmonics don't cause too much interference.
Transmitters with a crystal also use a tuned circuit with a coil.

I just looked in Google for Walkie Talkie Circuits and found a few. It even had a link to a thread here about walkie talkie circuits.
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Old 29th December 2007, 02:38 AM   (permalink)
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Audioguru,
I spent alo of times in Google for that, but not found yet. Ok now I understand that. Actually, I have a walkie talkie schematic attached. Receiver and oscilator coils are from 0,5mm on oscilator coil 8mm with 9 turns. RFC is from 0,5mm on 0.5cm free air coil with 33 turns.


my problems are :
1. I don't have a 27Mhz signal generator to tune that circuit. Can you help me?
2. The sound modulation is very low. How to solve this problem?
3. How to increase the distance?
Thank's for help.
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File Type: jpg walkietalkie003.jpg (268.0 KB, 58 views)
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Old 29th December 2007, 03:12 AM   (permalink)
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Your walkie talkie doesn't work well because it is cheap.
Its parts cost about $2.00. It cannot be tuned.

The schematic has an error: The collector of Q1 is supposed to connect to something with negative DC on it.
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Old 6th January 2008, 08:39 AM   (permalink)
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Dear Audiguru,

I would like to build your FM Transmitter, but I have the dificulties to find transistor 2N3904 in my town. I would like to substitute Q1 with C829 for preamp mic, Q2 with C930 and Q3 with C930 or C1970. Is it possible to do?
Thank's
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Old 6th January 2008, 11:51 AM   (permalink)
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Try the 2N2222A, those transistors you suggested sound really old.
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Old 6th January 2008, 04:16 PM   (permalink)
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The 2N3904 transistor is extremely common. Maybe it is not available in the Orient. A BC547 is almost the same but its pins are reversed.

The old Yapanese transistors are completely different.
The max allowed collector current for the 2SC930 is only 30mA.
The 2SC1970 power transistor has a huge range of hFE from 10 to 180 and its capacitance is too high.
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Old 6th January 2008, 11:48 PM   (permalink)
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2N2222 sounds common for me. I'll try to find it. And is it possible to modify it as a PLL Transmitter with the PLL module from http://www.pira.cz/enpll.htm? How to connect it inside your Transmitter?
Thank's for help.
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Old 7th January 2008, 03:42 PM   (permalink)
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My FM transmitter does not have a voltage-controlled oscillator. Usually they use a varactor diode which is tuned with the output voltage from the PLL circuit.

Why don't you make a kit or make your own Micromitter? It has a quartz crystal and a PLL and it is stereo.
http://electronics-diy.com/schematic...ransmitter.htm
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Old 7th January 2008, 09:08 PM   (permalink)
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Older thread -newer question

How long is the red wire antenna on your transmitter audioguru?f
From the point of attachment to the board.

Have you experimented at all with a very fine wire which will tend to sharpen the bandwith
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Old 7th January 2008, 09:20 PM   (permalink)
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Quote:
Originally Posted by tytower
How long is the red wire antenna on your transmitter audioguru?f
From the point of attachment to the board.
I tried it with a quarter-wave length. 80cm.

Quote:
Have you experimented at all with a very fine wire which will tend to sharpen the bandwith
The tuned circuits and the amplitude of the modulation determine the bandwidth, not the wire gauge of the antenna.
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Old 9th January 2008, 09:18 PM   (permalink)
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Quote:
Originally Posted by audioguru
The tuned circuits and the amplitude of the modulation determine the bandwidth, not the wire gauge of the antenna.
I take it you are not a radio ham?
Wire cross -section of the antenna is quite a factor at HF
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