Can i combine 2 different modulation schemes

[prototypingfool]

I'm in concept mode and wondering if i have two distinct carriers, say at 400MHz (not the freq) and one is FM modulated and the second is FSK modulated and i then run
them through a signal combiner.

Will i be able to decode both signals at the receiver?

Guessing,
PF

 

[VEBill]

FSK (Frequency Shift Keying, if that's what you really intend) is a form of FM. In practice, AFSK (Audio FSK) is more common.

The three basic types of modulation are AM (Amplitude Modulation), FM (Frequency Modulation) and PM (Phase Modulation). FM and PM are so closely related that there's little to distinguish them in practical terms.

Even trying to combine AM and FM on one carrier is basically impractical. There would be transmitter issues with linearity for AM vice efficiency of Class C for FM, crosstalk due to slope demodulation, limiting in the receiver, violation of regulations, etc.

What can be done is to use subcarriers, and then each of those can be modulated in any manner you choose.

 

[VEBill]

I think I missed the following: "...if i have two distinct carriers..."

If the carries are distinct (separate frequencies), and the signal combiner is linear (as it should be), then the signals will remain distinct.

So they won't interfere with each other at all (given many reasonable assumptions).

 

[prototypingfool]

VE1BLL,

concept is to send 400MHz voice into port j2 of a combiner and 400.1MHz data (some type of modulation) on J3 of a combiner and at J1(common) both signals would pass to an antenna over the air. Here is the guess. On the receiving end could i reverse the process RX antenna J1 takes signal and splits them (-3dB) and from J2 can recover the voice (fm) and on J3 recover the data.

 

[VEBill]

Basically - no problem. But...

To combine two transmitters into one antenna typically requires a specific type of combiner. It needs to provide high isolation from one transmitter port to the other. And when you consider the implications of refelcted power from the antenna (VSWR), then you probably would require frequency-based filtering (duplexers), or directional couplers and loads.

It may be far cheaper to add one moore antenna.

The most important practical exception would be if the two transmitters are very low power, then it may not matter much from a practical point of view (so long as the loss is not excessive).

 

[prototypingfool]

Thx Doc!

F