Variable Freq Oscillator

[mvs sarma]

thank you very much!!! Finally I'm starting to make sense of this circuit.

i just seacrh on google for crystal oscillator n there are loads of them...some for some kinda clock counter and some for coverter or somethin like dat. My questions are

1) is there a particular type of crystal oscillator needed for the task at hand or do i need to design and build a circuit for this or can i just buy one?
if i can buy one..is there any speification i need to know about?

2) when uisng signal generator as u explained above, do i need to set both the "audio tone" and the "RF signal's frequency" or re they mutualy exclusive? (sorry I havent used one before...lol)

3) Also, i was talking to a friend and he said a crystl oscillator can aso be used as the external oscillator ciruit that controls the internal one... UR COMMENT ON THIS WILL BE GREATLY APPRECIATED!

Thanks

1. you might use any signal generator available with you. what i suggested was, you can try to make a modulated signal generator at 3.579MHz using a cheap crystal and few components.. if there is any HAM transmitting in that bans you can ask him to send a test test tone and you can tr y to receive it. then no need of signal gen.i forgot- you can switch on and off the oscillator and this becomes a sort of interrupted rf signal like morse code.

2. if u use adio mosulation you can hear the tone while testing. other wise only carrier, also you can do as you can adjust your BFO and get the tone.

3.already your chip has facility for internal oscillator and you can manage witha coil, as you wanted a range like 3.5 to 3.7MHz. this range wont be possible with external crystal oscillator as local oscillator.

 

[chongjinyang]

mvs sarma,

forever99482 has been away for a while so he couldnt reply you. Me and him are in the same group working on the project. Anyway, we got the TCA 440 from a small supplier in UK. We are from Malaysia but studying in UK so im sorry we cant help you find out the availability of TCA 440 in Malaysia.

By the way, i noticed that the tuning oscillator isnt ganked to the tuning antenna resonance circuit. Thus, if i would want to receive a diff radio freq. how is it possible to tune both according to the equation IF = RF - LO. Are both tuned individually to achieve that? Or is this circuit just made for a specified freq.?