Hello,

You could make a FSK modulator at a lower frequency and mix it up to this ISM band.

Greetings,
Bertus

 

but whats wrong with just using this only IC and making an FSK signal......

why going through the long route.....

may be u r talking abt a freq synthesizer.... bt i wont really like that.... because its going to be too messy... i'd just stick to the plan.... can u plz help me with this example....


a CD4046 example:

lets say i've an FSK signal with 600KHz as low freq and 625KHz as hi freq.... now i've to demodulate this signal..... which means i've to keep the free running freq of the VCO to 615KHz.... the lock range to like +-70KHz or watever and the capture range to +-30KHz.... now how do i design this.... i cant use the formulae to make a demod which can capture the above signal.... plz tell me that what should i keep the value of the R3 and C2???? plz anybody do these calculations for me and show me how to you did it.... i'll be deeply indebted.....

 

Hello,

What I am talking about is normal practice.
The FSK signal is made in audio say 1000 and 2000 hz.
Modulate this in AM or FM on the carier frequency in this ISM band you named.

To recieve it, make an AM or FM reciever for the same frequency and demodulate the 1000 and 2000 hz back to you digital signal.

Greetings,
Bertus

 

yeah.... someone previously did that.... bt i dont think its a good idea to modulate two times..... if u r doing FM modulation then whats the point of doing FSK???? sir plz help me with the example.... besides if i've a PLL IC with a VCO that could be used alone upto 13MHz.... y would i go for two modulation techniques...... its not a smart thing to do i guess......

 

Hello,

You could use the basic schematic :

Use for the divider N=2712 for the 0 and N=2713 for the 1, use for input 5 khz (preferably from a xtal timebase).
Use comparator 1 , this will also lock on harmonics.

Greetings,
Bertus

 

i've done these calculations..... and simulated them and by the Grace of ALLAH i'm close ..... bt there is a bit of error... can someone plz check my calculations etc....

 

Hello,

Again you are out of the ISM band.
Take a look at this picture to calculate the R1 R2 and C for the oscillator.

Greetings,
Bertus