Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
Here is what I see:
1.) There is a 8Mhz crystal that is oscillating into Q1, effectively turning it off and on
2.) C2 is used to filter the DC from the oscillator
3.) DC biased voltage divider mixed with the ASK reasonator that feeds into Q2
4.) Resonating signal is filtered by C4
5.) analong input controls the Q3 transistor
6.) The analog signal is mixed into the reasonating carrier signal
7.) Resonating carrier signal is amplitude controlled with mixed analog input signal
R1 provides the base bias for Q1 so yes it is kind of important.
The feedback is via the crystal which wil be run at its series resonance.
This thing is not a very good transmitter, it will have poor modulation linearity and needs an output filter to ensure the RF harmonics are sufficiently attenuated, the common base 'power' (maybe 10dBm or so ?) stage is kind of interesting howevr.
I wonder to what extent those overly large 1uF coupling caps contriute to modulation by allowing audio input to change the bias point of the previous stage (I am not curious enough to spice it)?
The best thing to do is to replace R8 with a tuned circuit. If your aerial is 300/ 4 X F m. long then its a good aerial ( 9m), if the aerial is shorter then it needs an inductor in series with it to tune it and the aerial should be connected to a tap on the new tuned circuit (~ 10 % away from the Vdd end). So now you have two additional tuned circuits, both of which reduce the harmonic output and increase the output.
Frank
The best thing to do is to replace R8 with a tuned circuit. If your aerial is 300/ 4 X F m. long then its a good aerial ( 9m), if the aerial is shorter then it needs an inductor in series with it to tune it and the aerial should be connected to a tap on the new tuned circuit (~ 10 % away from the Vdd end). So now you have two additional tuned circuits, both of which reduce the harmonic output and increase the output.
Frank
5.) analong input controls the Q3 transistor
6.) The analog signal is mixed into the reasonating carrier signal
7.) Resonating carrier signal is amplitude controlled with mixed analog input signal
This thing is not a very good transmitter, it will have poor modulation linearity and needs an output filter to ensure the RF harmonics are sufficiently attenuated, the common base 'power' (maybe 10dBm or so ?) stage is kind of interesting howevr.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
