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Help me with graduation project about digital RF data link

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ahmad_abdulghany

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zw3102

Hi
I am working in my graduation project now, it aims to design, simulate, and implement a digtal RF data link.. As a first thing, we hope to succeed to implement it with the following requirements:

- Data bit rate > 3 kb/s
- FM Tx/Rx with carrier ≥ 50 MHz
- Coverage Range (distance between Tx and Rx) > 5 meters
- Stable
- Made with discrete elements only (Transistors, R, L, C, and No ready modules)
- Moderate antenna length (not very long)

Can anyone help me please, add any suggestion, It will help me for sure!
Thanks alot in advance,
Ahmad,
 

IanP

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Re: Help please

Have a look at the circuit below ..
It is a simple 433Mhz data link ..
Maybe you can use it as a good starting point ..

Regards,
IanP
 

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ahmad_abdulghany

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Re: Help please

thank you very much IanP
It looks interesting,
but the problem that i can't understand a word from the text written! Which language is it?!
If you can translate it into English, it will be kind of you, and pleeeeeeez, keep helping me don't abondon me..

Thank you again, and go on!
Ahmad,
 

IanP

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Re: Help please

I am not a linguistic guru and I also don't understand some of these words (written most likely in DANISH), although I can't find many interesting details in the text description ..
It says that the receiver type is "super-regenerative" of which you can read, for example at https://en.wikipedia.org/wiki/Regenerative_circuit ..
Also, the designer claims (in the bottom part of the text ) that this circuit should be able to connect two computers via their COM ports for over 100m ..
That's all ..

Regards,
IanP
 

ahmad_abdulghany

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Re: Help please

thanks for replying again.
please do add some short comments on the red named boxes in the attached picture..
Specially numbers: 3,4, and 5..

And for number 5, I think it's an IC where to get...
Thanks in advance,
Ahmad,
 

IanP

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Re: Help please

3 & 4 -> antennas which can be drawn directly on PCBs and 20mm x 10mm are their diamentions .. The track width can be ≈1-2mm ..
5 -> The TL082 is general purpose dual BIFET opamp .. In this application it can be easily replaced by any rail-to-rail dual opamp (LF353, CA3260, ..) or can be build of 2x single opamps ..
7 & 8 -> any NPN RF small signal BJTs rated for Ft≈1000MHz ..

Regards,
IanP
 

ahmad_abdulghany

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Re: Help please

Hello IanP
I am really unable to express my thanks to you for your great valuable help!

But I am sorry to ask you for further more help.. Can you explain the operation of the two circuits above (in details as possible if you don't mind), I am ashamed to ask you for I'm sure that you will help if you can,

By the way I am looking for some alternatives to the Dual FET opamp IC, and the RF BJT (with that high ft) as they're not available here, so if you can tell me about some alternatives,...

Or, I dont' know in fact what should i follow if I need a component that is not available, how to get an alternative for it? :)

Thanks in advnace and for patiency,
Ahmad,
 

IanP

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Re: Help please

There is nothing special about this opamp, you can use virtually any opam, if you have 358, 324, 741 .. any will work ..
The first opamp is just an amplifier (pin2=input, pin1=output), the second opamp works as comparator (pin5=input, 1/2supplyvoltage=pin6, output=pin7) ..

As for RF transistors, if you can't buy them you can find them in any old VCR or TV VHF/UHF tuner ..

Regards,
IanP
 

ahmad_abdulghany

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Re: Help please

Hi IanP

First, what are values of coils, and i want an explaination of the circuit
I just now want to build this circuit, but i wonder about some things, how far bit rate can it reach? also, can you give more specs about it?

Can't i reduce the power supply voltages? What about coverage range in this case?

Alslo, where that 433 MHz came from ?!? Can't I change it?

Thanks in advance,

Ahmad,
 

Borber

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Re: Help please

Maximum bitrate for this receiver without modifications is about 2kb/s.
Circuits can work with lower supply voltages but need to be adjusted.
Lower transmitter supply voltage will reduce max. communication distance. For distance of few meters, I think you will have no problem.
Frequency 443MHz is allowed in Europe for this type of short range communications without need for license.
Frequency can be changed. But significant change of operating frequency require circuit modifications and selection of different type of antennas. In this case a loop antenna is used which is actually inductor in tank circuit.
 

ahmad_abdulghany

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Re: Help please

2kbps?!! Very low bit rate!
Can't i find similar Rx/Tx circuits working either at same frequency or lower but have higher bit rate with distance not less than 100meters?

Thanks in advance,
Ahmad,
 

IanP

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ahmad_abdulghany

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Re: Help please

IanP said:
Maybe you should consider "EL CHEAPO" 433-434MHz off-the-shelf modules ..
Take a look at, for example, the budget pair ZW-3100 (transmitter) and ZW-3102 (receiver):
https://www1.electusdistribution.co...D=31&keywords=&SPECIAL=&form=CAT&SUBCATID=109
You can treat them the same way as you would treat an 7400-series chip, or an BCXXX transistor ..

Regards,
IanP

But building the Rx was my aim not to by a ready module! I need to build it my own! Cant you help me in that?

or it's impossible to build it discrete with that specs??
 

eldo

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Help please

It is Dutch!
 

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