Hi all,

I'm doing a project FM TX and RX design without using any help of IC.
The frequency band is choosen to in 40.xx Mhz for the project. This is the ISM band.

Please purpose if you have any.

TQ

 

http://www.dmoz.org/Recreation/Radio/Amateur/Homebrew/

 

Hello,

Did you already have a look in the RF related links thread?

Basicaly the change to an other frequency is changing the tuned circuit of the transmitter and reciever.
For better stability take a look at some transmitters using an X-tal oscillator.

Bertus

 

Tq for quick reply bertus, i was not sure about changing the "inductance" tank circuit could actually achieve the desire frequency.

Thx for your hint, i will focus into that area.

 

You can build a transmitter using a crystal to lock your frequency. Google is your friend. There are hundreds of thousands of hits for crystal transmitters. It is up to you to choose one depending on the complexity of the circuit you want to build.

 

Radiohead, i hv no idea which 1 is more compact and stable and i;ve no idea choosing any.

 

I built this one. It works pretty good. With a little tweaking and maybe adding a PA stage with a matched antenna, you can achieve a mile or more (line of sight).

 

Good info, thx radiohead

 

Hi all,
I got updated from my supervisor, he requests me to use VCO to build the transmitter and fix the output frequency to 40.xMhz.

Can any 1 share the concept or idea?
i'm still fresh

 

Hello,

In wich way must the frequency be fixed?
Can you use a PLL?

Bertus

 

Hi bertus,

Yes, PLL can be included. Anyway, how could i fix the FM TX center frequency to 40.68 Mhz using VCO + PLL. Sounds like the TX getting complex.

 

Hi all,

I would like to make clear on something. I just updated from my supervisor, he has told me to try achieved the modulation index, B ~ 5.0 (if possible).

My project is basically design a FM transceiver.
Input : microphone (human voice)
Output (TX) : able to produce the (human speech)

Design requirement
TX :1.Frequency must be ISM band ~ 40.6Mhz.
2.The design must stick with VCO + PLL.
3.Intergrated circuit is restricted for designing the VCO.

RX : The design could use IC to implement and must be able to receive the correct signal.

 

Hai all,

How can i control the frequency deviation?
What is the max modulating frequency if the input is human voice to micophone?