Hi,
I'm designing a circuit that will take a square wave generated by a microprocessor and feeds it through a bandpass filter to get a sine wave. The application will be to provide a tone for morse code to a handheld ham radio on board a small satellite. Right now im considering remaining simple by using a 1st order passive bandpass filter that uses a capacitor and inductor in series. Assuming this I have a few questions.
1) How should I choose the impedance of the bandpass filter? I do not know the impedance of the GPIO of the microprocessor. Does this impedance matter much?
2) Should I filter more to get a truer sine wave? Any experienced hammers out there? I will be transmitting the morse code tone from a ham radio from a 400km orbit (LEO). I will then feed the tone through a morse decoder to convert the morse to text using a freeware program.
3) Finally, I wanted to use a passive filter to save power, however, I'm open to an active filter that uses an opamp. Are there any advantages to this?
4) What would the gain of a 1st order series LC filter be at the center frequency? I know that the coefficient of the Forier series for a square wave is (4/pi)*Vpp of square wave. I would like to take the output of the bandpass filter and scale it down to 5mV at 2000ohm at knowing the gain of the filter I decide to use would be good for calculating the scale factor.
If possible, could you provide references for your answers so that I can have good confidence in the answers? Any guidance would be greatly appreciated!
Thanks,
Windell
I'm designing a circuit that will take a square wave generated by a microprocessor and feeds it through a bandpass filter to get a sine wave. The application will be to provide a tone for morse code to a handheld ham radio on board a small satellite. Right now im considering remaining simple by using a 1st order passive bandpass filter that uses a capacitor and inductor in series. Assuming this I have a few questions.
1) How should I choose the impedance of the bandpass filter? I do not know the impedance of the GPIO of the microprocessor. Does this impedance matter much?
2) Should I filter more to get a truer sine wave? Any experienced hammers out there? I will be transmitting the morse code tone from a ham radio from a 400km orbit (LEO). I will then feed the tone through a morse decoder to convert the morse to text using a freeware program.
3) Finally, I wanted to use a passive filter to save power, however, I'm open to an active filter that uses an opamp. Are there any advantages to this?
4) What would the gain of a 1st order series LC filter be at the center frequency? I know that the coefficient of the Forier series for a square wave is (4/pi)*Vpp of square wave. I would like to take the output of the bandpass filter and scale it down to 5mV at 2000ohm at knowing the gain of the filter I decide to use would be good for calculating the scale factor.
If possible, could you provide references for your answers so that I can have good confidence in the answers? Any guidance would be greatly appreciated!
Thanks,
Windell