You did not mention the purpose of the circuit yet you are interested to build this, which is quite baffling to me. Any way, it seems a receiver circuit built with three stages. First, the transistor is used as an RF Oscillator, amplifying the RF signal picked up by the antenna, which is being fed into the 2nd stage non-inverting operational amplifier. The amplified sine wave signal is being converted to square wave by the last 3rd stage op amp, used as a comparator to give the final data out put in the form of square wave that is an stream of zeroes and ones depending upon the edges of the square wave. For the value of the coil, you must know the frequency of the tuned circuit in your diagram.Oki, I got this DVD in german, BUT there are all pages, but page 54 there isn't. There are page 53 and next is page 55! Amazing!
So maybe someone who have this magazine at home can scan it?
Or if in this forum is some circuit expert who can explain me this circuit, please help me:
Receiver circuit is for 434MHz OOK modulation. So I colored 4 main questions.
1. The basic interest is in L1 * (*1,5turns), there isn't shown coil diameter and wire diameter. I have calculater from Thomson's equation (f = 1/2*pi*sqrt(LC)) that L = 67nH if I use C = 2pF. Is that correct? Also, can I use smd - 67nH?
2. What do this part?
3. Is this pulse modulator with OP? Maybe someone can explain what does it do?
4. Never seen befor OP Amp circuit like this, is there something missing? Maybe there is feedback needed? And what it do? All I know, that both these OpAmps amplify the signal.
Hi Kaspars! So, you have two questions!Hi,
Thanks tgotwalt1158 for your answers
I have nevar built any UHF receiver/transmitter so my expierence is very poor, that's why I really appreciate any recommendations/suggestions/instructions in this field.
First of all I would like to inform, that I have built 434MHz OOK Transmitter. Here is circuit:
And here you can see how I made it (Used SAW resonator 434MHz):
Input signal is asynchronous binary signal with amplitude ~5V (Red line). When I use oscilascope before antenna I get this (blue line):
When I use Spectrum Analyzer I get this:
Channel power is about -30dBm, that's about 1uW.
So my first question is:
1. How can I increase channel power?
After that I have made receiver (circuit shown in my first post), here is picture:
At the antenna output received signal amplitude is ~50mV:
Also I noticed, that 17cm antenna is too big, and decided to make transmitter/receiver with 868MHz or 2.4GHz.
2. Maybe someone have some circuits for 868MHz or 2.4GHz transmitter/receiver? Can I make it the same I did for 434MHz just changing some components?
Yes I know there are a lot of 2,4GHz modules, but they all are for sychronous systems, but my input signal is from Time encoding Machince (TEM) which is asynchronous, so building transmitter/receiver is difficult.
Thanks for help.
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by Jake Hertz
by Steve Arar