# Need Elektor Electronics July/August 1993

#### Kaspars

Joined Jun 9, 2011
17
Hi Everyone,

1993 magazine. If some one have it, please inform me.

Also I you have it in home, maybe you can scan page 54.

Thanks

Best regards,
Kaspars

#### t06afre

Joined May 11, 2009
5,934
What kind of circuit is you want. Even if we do not have the latter magazine we may help

#### atferrari

Joined Jan 6, 2004
4,379
Elektor supplied, at least with the Spanish version, copies of several years in CD.

Hope that helps

#### SgtWookie

Joined Jul 17, 2007
22,221
Elector sells a DVD with 1990 thru 1999 editions on it for ~$113. Thread Starter #### Kaspars Joined Jun 9, 2011 17 Yes, I know about spanish version, but UK version is different, so this article isn't in Spanish ver. magazine. Last edited: Thread Starter #### Kaspars Joined Jun 9, 2011 17 Elector sells a DVD with 1990 thru 1999 editions on it for ~$113.
I don't want to spend 113\$ just for one article :/

#### t06afre

Joined May 11, 2009
5,934
Perhaps a library may have what you want

#### Kaspars

Joined Jun 9, 2011
17
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?

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#### tgotwalt1158

Joined Feb 28, 2011
110
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.

Thanks.
Best regards,
Kaspars
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.
This is general circuit analysis. If we see in perspective of OOk that is on-off key modulation, the RF portion could be viewed as band pass filter, the middle portion is responsible for envelope and peak detection, which are the components of OOK de-modulator.

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#### Kaspars

Joined Jun 9, 2011
17
Hi,

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#### tgotwalt1158

Joined Feb 28, 2011
110
Hi,

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.

Best regards,
Kaspars
Hi Kaspars! So, you have two questions!
1) You could use the ADF7901 for increasing power of transmitter with a higher frequency of your choice. Here is the data sheet of ADF7901 :