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| General Electronics Chat This forum is for general chat about electronics, eg: Dont know what a part does? Dont know how to read a circuit? Want to get an opinion? |
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15th February 2004, 12:54 AM
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 rf transmitter + receiver circuit, what's wrong... hi, now this is my first rf project i attemp to build , i wanted to use linear ICs cause they make things a litle easier and with less error factor! now i've got those 2 circuits from an old printed sheet, but they dont work at all.. the emiter seem to be working cause i am getting kind of disturbance in a nearby fm radio.. but i dont know , please send me corrections. l1 and l2 are 5 truns copper 0.5 cm diameter 1 cm length without a core inside. i have experimented with many many values for resistances and capacitors.. so now i am so confused!.. i would apreciate giving me ideal values (approx.) for the resistances and capacitors. thx a lot everybody. | |
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15th February 2004, 02:41 AM
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| receiver & transmitter From your discription of the coils the frequency my be for the standard broadcast band 88-108Mhz. The actual frequency for the transmitter is determined by the inductance of L1 and the capacitance of C2, plus other capacitance in the circuit. The output of the 555 timer is a pulse wave form that may excite the tuned circuit, but as far as modulation that is questionable. The receiver circuit has no detector between the tuned circuit L1 and C4. The op amp is a standard amplifier, and will not respond to the RF of the input unless it is low in frequency. You might post the values of the other components so we can help you better.
__________________ The great thing about electronics is unlimited ways to do the job. The only limit is one\'s imagination. I generally think my way is best. Show me a different way. I have an open mind. | |
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15th February 2004, 10:32 AM
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| Maybe the designer thinking with BJT input opamp, and the first e-b can work as rectifier. | |
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15th February 2004, 05:44 PM
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| check out these sites for a better design: http://www.geocities.com/tomzi.geo/1...transistor.htm http://www.somerset.net/arm/fm_only_...tor_radio.html
__________________ see my website: www.geocities.com/russlk | |
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15th February 2004, 08:23 PM
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| actually what is the difference between rf for voice carying and rf for remote control. i mean, okay i can send my voice through rf and it is not very clear.. but what if i want to send the state of a switch, what are the changes that have to be made on 100% of the circuits i find on the net that allways include a mic. i dont need a mic but a switch instead! any hints? | |
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15th February 2004, 09:13 PM
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| You need a signal source, like an audio oscillator, that can be turned on & off. At the receiver, no signal = switch off, signal = switch closed. The audio oscillator could be the same circuit as the RF transmitter, with different L & C.
__________________ see my website: www.geocities.com/russlk | |
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15th February 2004, 10:32 PM
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| russlk, so how do you make an "on" button that when the receiver recieves a signal, it stays on even when the signal is removed? one shot 555 a good idea?
__________________ thanks, david | |
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16th February 2004, 01:52 AM
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| A flip-flop would be better. If yu use the clock input, one pulse could turn on and the next pulse turn off.
__________________ see my website: www.geocities.com/russlk | |
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29th March 2004, 06:15 PM
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| did you ever get this working? I belive we are trying to build the same project, but i have been having no luck. please let me know david
__________________ thanks, david | |
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31st March 2004, 02:17 AM
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| does it matter the pulse rate you set the 555 to?
__________________ thanks, david | |
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