I'm doing a FM tranceiver project. The FM TX is required to produce output frequency of 40.x Mhz which is ISA band. The TX is also required to stick with VCO design. I;m stuck with the design.
You did not give much details of what modulation index you are looking for.
For narrow band FM, a common method of modulation on a synthesizer is called two port modulation. A varactor on the RF VCO and varactor in the crystal reference oscillator is modulated in exact proportions to result in net zero frequency delta as seen by synthesizer phase detector. This avoids the issue of synthesizer correcting out modulation only placed on RF VCO.
Newer Frac-N synthesizers do this directly on synthesizer by digitially modulating the dividers as well as the RF VCO. Same objective, to keep net zero frequency shift on the phase detector.
Hi all,
I;m new to FM design. In fact, i;m still fresh to learn. My supervisor has told me to try achieve 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 signal.
Thx Tony. Do u hv any suggest on VCO? i've searched through the google, there were lots of oscillator design, colpitts (series or paralle) , Hartley. I've no idea which 1 i should choose.
Is there any simulation could be used before going to actual design?
I;m currently using ADS software, i was wondering how can i use it to identify whether the design could work or not.
You can look up SA605 it is an FM IC which you can use fro the receiver. In the case of transmission you can use a LC circuit to generate the oscillations. Then you create an antenna well if you use copper your looking at an antenna length (full length ) (0.951)*c/freq = wavelength antenna. an omni- directional could also be salvaged from an old radio.