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rf transmitter + receiver circuit, what's wrong...

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ikalogic

Member
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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k7elp60

Active Member
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.
 

Sebi

Active Member
Maybe the designer thinking with BJT input opamp, and the first e-b can work as rectifier.
 

ikalogic

Member
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?
 

Russlk

New Member
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.
 

daviddoria

New Member
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?
 

daviddoria

New Member
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
 
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