Hello,
I'm a wildlife biologist attempting to understand and modify a "simple" RF transmitter created for use as a small-animal telemetry transmitter (see my previous 2 posts here and here for details of the original design). I have been attempting - unsuccsessfully - (for a number of years) to simulate this circuit to better understand how it works, and to modify it to work as a MCU-controlled transmitter, and could really use some help with troubleshooting the PSPICE model.
I am aware that simulating a crystal oscillator is tricky, but that it can be represented relatively well as a shunt capacitance and RLC circuit in parallel. I have found a forum post about simulating a 27 MHz crystal here, but it is unclear exactly how the R, L, and C values were obtained. Since the circuit I'm trying to simulate has a 48-49.5 MHz crystal (with a filter that emphasizes the third harmonic), I'll need to modify these R, L, and two C values with something moderately realistic for this frequency of crystal (of course, all of these values are not provided by the crystal datasheet; I'm using a 48 MHz NX2520SA). I'm not looking for anything too exact here, I'm just hoping to get the circuit to oscillate and pulse (i.e. RF pulses controlled by the RC circuit of R1 and C1 in the attached diagram) in a way that vaguely resembles what the circuit does in real life.
Any thoughts?
Many thanks!
-Julian
*Note that the values I have for CS, CL, RL, and LL are based on the 27 MHz crystal forum discussion and are therefore wrong for this circuit! As recommended in the referenced forum post CL has been set with an initial condition of 5 kV to "jump-start" it.
**Also, you might notice that I'm using a Q2N2222 NPN BJT as T1 here, not for any reason other than that the RF BJTs I'm using do not have PSPICE models available. If this is likely to interfere with the basic functionality of this simulation this is an issue that will need to be resolved, but I'll otherwise cross this bridge when I get to it.
I'm a wildlife biologist attempting to understand and modify a "simple" RF transmitter created for use as a small-animal telemetry transmitter (see my previous 2 posts here and here for details of the original design). I have been attempting - unsuccsessfully - (for a number of years) to simulate this circuit to better understand how it works, and to modify it to work as a MCU-controlled transmitter, and could really use some help with troubleshooting the PSPICE model.
I am aware that simulating a crystal oscillator is tricky, but that it can be represented relatively well as a shunt capacitance and RLC circuit in parallel. I have found a forum post about simulating a 27 MHz crystal here, but it is unclear exactly how the R, L, and C values were obtained. Since the circuit I'm trying to simulate has a 48-49.5 MHz crystal (with a filter that emphasizes the third harmonic), I'll need to modify these R, L, and two C values with something moderately realistic for this frequency of crystal (of course, all of these values are not provided by the crystal datasheet; I'm using a 48 MHz NX2520SA). I'm not looking for anything too exact here, I'm just hoping to get the circuit to oscillate and pulse (i.e. RF pulses controlled by the RC circuit of R1 and C1 in the attached diagram) in a way that vaguely resembles what the circuit does in real life.
Any thoughts?
Many thanks!
-Julian
*Note that the values I have for CS, CL, RL, and LL are based on the 27 MHz crystal forum discussion and are therefore wrong for this circuit! As recommended in the referenced forum post CL has been set with an initial condition of 5 kV to "jump-start" it.
**Also, you might notice that I'm using a Q2N2222 NPN BJT as T1 here, not for any reason other than that the RF BJTs I'm using do not have PSPICE models available. If this is likely to interfere with the basic functionality of this simulation this is an issue that will need to be resolved, but I'll otherwise cross this bridge when I get to it.