Can I par up FSK transmitter and ASK receiver?

[Evo]

Dear all,

i have a doubt.... say if i have a FSK transmitter (27MHz) and an ASK receiver (27MHz), can i pair them up? what will i receive at the receiver side if i send a digital pulse through this transmitter?

 

[trigger74]

power spectrum of fsk

Both modulations are different... how can they compatible each other........

 

[Mr_Programmer]

Re: ASK and FSK

Well it is possible at all!
Basic idea switch the FSK transmitter on and off, so you can OOK/ASK modulate the carrier frequency. Easy isn't it? :wink:
Some points to remember: check the frequencys of the FSK transmitter (f0 and f1), you must send 0's or 1's to match the center frequncy of your ASK receiver...
If I think about this a little bit more ... hmmm ... could be the best to modify the FSK transmitter to transmitt only OOK

Regards...

 

[biff44]

Re: ASK and FSK

Are you simply trying to sent 2 bits of data? Assuming you are using the same carrier frequency for each, combining ASK and FSK may not work too well for a number of reasons. If you send a string of 0's on the ASK, there will be no carrier for the FSK to send on. You will also need 2 seperate receivers, because most FSK systems use a limiting RF amp that will strip off ASK.

Why not use 2 bit phase modulated signal?

Added after 1 minutes:

Or if you like FM systems more, how about 2 bit FSK (4 frequency levels).

 

[Evo]

Re: ASK and FSK

hey,

regarding the question, i have a reply from an expert whose explanation is as below.


FSK consists of two carrier frequencies. The frequency changes depending on the symbol 1 or 0 used. Mathematically can be described as:
s(t) = f1(t) (2*pi*fc1*t +phase) + f2(t) (2*pi*fc2*t +phase)
So, in power spectrum, there are two signals f1(t) and f2(t)

ASK is amplitude modulated signal which the amplitude changes depending on the symbol 1 and 0 used. Mathematically can be described as:
s(t) = f(t) (2*pi*fc*t +phase)
So, in power spectrum, there is only one signal f(t)

If a signal is transmitted with FSK TX, and received with an ASK RX, you will lose some information. ASK RX only care about one frequency and looking for the amplitude change (using envelop detector) in the signal. As a result, if the signal received is more than 1 frequency, it will be rejected.

ASK and FSK are different modulation scheme. As far as I know, you can't use FSK TX and expect ASK RX to recover the information.



Dear biff44,
can you explain further, i couldn't get you...

 

[biff44]

Re: ASK and FSK

I think you do not understand the concept of a RF spectrum. If you transmit only ASK, and modulate with a random pattern of 0's and 1's, there will be more than just a carrier at the very center frequency. There will be a small carrier, and lots of sideband energy at frequencies related to the modulation clock rate. Search the web for some spectrum pictures of AM modulated waves.

This is why Broadcast AM radio stations need to be spaced across the radio's frequency dial. They use a "bandwidth" of energy to send the music, even though they are using AM only. If the stations are spaced too close together in frequency, their spectrums overlap and cause distortion.

 

[Evo]

Re: ASK and FSK

ic... now i get you...

thanks.