circuit diagram for wireless speech transmission

Hey guys

I'm trying to implemnt an analog wireless speech transmission circuit having PLL and VCO in the local oscillator part and I will use the 433 ISM frequency band.

Fistly, I did not have an idea about how I do the project. I came across a circuit which works in the FM band, 88-108MHz. [img]fm_500.gif[/img].

I looked at the datasheet and and application notes of the LMX2306.However; there is less information to understand.

Do you have any idea about how I can implement the circuit? I am open for any kind of sugession.

looking forward to hearing

Circuit looks to be ok to me. ensure that BC817-25 and BRF 93A provides the VCO, modulation and amplification.

The top circuits built arround BC817-25 and BRF 93A looks ok which modulates the audio and other the power amp sections. But how are you going to vary the frequency of the band, and hope you have got the firmware for the PIC microcontroller. Good luck.

I am suspicious of the 100K ohm resistor between the "vtune" test point and the varactor diode. That value may be too large. You might have to lower to 10K, or even 2.2K.

That resistor is used to pass DC tuning voltage to the diode (which changes capacitance vs applied DC voltage), but also serves to block the RF power from running down the line back to the PLL chip. But if there is any leakage current to ground, the PLL chip may not be able to overpower the high (100K) resistor value.

If you are looking for high quality audio, you MUST add a lowpass filter for the audio input. The lowpass filter must be sized to not let any audio frequencies above 15 KHz to get into the oscillator. This is because most FM radios (stereo ones) will flip out with higher audio frequencies, and fold them back onto the desired audio--causing severe distortion.

If you have any gear at all, test to see if the PLL is indeed working and locking the output frequency in a stable way to the desired channnel.

Don't expect a BC817 to oscillate at 433 MHz.

Hey guys

thanks for responses you sent

I suppose I can not explain what I will do. I'm not interested in the circiut diagram I attached. I put that picture to not to ask how I configure it to my project. there is less information or circuit diagram at the internet about PLL+VCO

I'll modulate the audio signal via a local oscillator. In the local oscillator part I'll use PLL+VCO. As I researching how to do that, I came across a product of Analog Device, ADF4360-7. I guess I will try that. However; I did not understand the oscillator part of the circuit. Is that a normal crystal oscillator? ıf so, why it has 3 terminals ?

Do you have any idea about How I can do a local oscillator using PLL and VCO ?


[img]adf4360-7.JPG[/img]