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Your 8-pole highpass filter is biased correctly and should work. Except the TL074 opamp does not go high enough.
EDIT:
Filter Pro says to use high speed opamps, especially the 4th one. The TL074 is too slow for this filter.
The filter will reduce the amplitude of the carrier a little as shown on the frequency response in the simulation.Thanks,
Can you let me know if I will have a good carrier at the output of the above filter?
The filter passes frequencies above 40kHz like a piece of wire (the TL074 goes up to 100kHz) so does not affect the bandwidth.I do not know if that 8pole filter is good for 10kHz of bandwidth?
It will work a lot better with the high speed opamps it needs.I fear of phase shift at the output of the above filter?
The LF411 and LF356 are not high speed. Look at what is needed on the Filter Pro simulation then look at their datasheets. I have never used high speed opamps.I do not know any high speed opamp. what are they? Do you think LF411 and LF356 are high speed opamps?
Of course a capacitor is needed at the junction of the two 1k resistors to ground. Try 10uF.P.s did you care of the single power supply and the 1k biasing resistor?? No need to capacitors for them?
I do not know how to read the values on the software graph.The filter will reduce the amplitude of the carrier a little as shown on the frequency response in the simulation..
If so maybe a one pole filter does work? So why we use the higher order filters?The filter passes frequencies above 40kHz like a piece of wire (the TL074 goes up to 100kHz) so does not affect the bandwidth..
Of course a capacitor is needed at the junction of the two 1k resistors to ground. Try 10uF.
You want a very sharp filter to cut the lower sideband. It has no effect on the upper sideband so has no effect on audio bandwidth.
A one pole filter will not remove much of the lower sideband and will also have no effect on the upper sideband.
The two 1k resistors bias the opamps. The bias voltage must be a low impedance so a capacitor to ground is used.
5% resistors are usually used so their small tolerance has a small effect on the operation of the opamps but only when their output level approaches max.
Ham radio operators use crystals to cut a sideband. Then the bandwidth is so narrow that you can't understand the chipmunk voices.Is the waver method a better way to go for instead of filtering method?
Ham radio operators use crystals to cut a sideband. Then the bandwidth is so narrow that you can't understand the chipmunk voices.
I don't know why your circuit is biasing capacitors at the bottom. Capacitors do not need a DC bias voltage.
Your 39KHz fillter is only 1KHz about the lower sideband with a 2KHz modulation frequency. That's why so much of the lower 2KHz sideband gets through. You should go to a 40KHz filter. That will reduce the lower 2KHz sideband and still leave significant carrier feedthrough as you desired.
You could also go to a filter with a faster rolloff such as a Chebyshev. That will give you some ripple in the passband response, but that should be tolerable.
What is the waver method?
I does matter whether the filter is 39KHz or 40KHz since it affects the suppression of modulation sidebands that are close to the carrier.It does not matter using 39kHz or 40kHz anyway. I want to transmit my voice or music so the modulating freq changes frequentely.
Go here for the waver method:
Single-sideband modulation - Wikipedia, the free encyclopedia
After 3 pages of this thread there is one question I must ask...
Why on earth are you wanting to create a 40khz single sideband, full carrier signal?
Not only that, but with a modulation frequency response extending to 10khz?
What possible application does it have? I seems like pure madness.
Please enlighten me.
JimB