Can you let me know if I will have a good carrier at the output of the above filter?
I do not know if that 8pole filter is good for 10kHz of bandwidth?
I fear of phase shift at the output of the above filter?
I do not know any high speed opamp. what are they? Do you think LF411 and LF356 are high speed opamps?
P.s did you care of the single power supply and the 1k biasing resistor?? No need to capacitors for them?
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.
P.s did you care of the single power supply and the 1k biasing resistor?? No need to capacitors for them?
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.
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.
A one pole filter is very simple so it filters poorly. For a highpass filter the amplitude is 0.707 at the cutoff frequency and is only 0.5 at half the cutoff frequency.
A filter with 8 poles has its amplitude at 0.02 at half the cutoff frequency so it reduces the low frequencies much better.
The capacitor at the bias voltage filters any signal away.
Ok I made the above 'Sallen –Key' filter in real with TL074.
Unfortunately it did not work at all (I do not know the reason).
So I went to design one filter based upon 'MFB Single-Ended'.
Now it does work but the output is gain seem to be less than one?
The bellow is the 'MFB Single-Ended' circuit designed by Filterpro and simulated by Pspice at 2kHz and then at 10kHz.
Because I am not able to put more than 3 pictures in a post I will post the FFT of the Pspice at 2kHz And 10kHz modulating signal in the bellow post.
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.
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.
Don't you know that old fashioned Amplitude Modulation (AM) is usually very narrow band, is full of static interference and interference from anything that operates near its frequency like compact fluorescent light bulbs and anything that makes sparks?
Wideband FM modulation is used for voice and music today.
I does matter whether the filter is 39KHz or 40KHz since it affects the suppression of modulation sidebands that are close to the carrier.
The Weaver (not waver) Modulator is a rather complex method of generating a SSB signal, generally implemented with digital circuits. It's much more difficult to implement then the simple filter method you are attempting.
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.
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.
Well several days ago I read a paper about creating audio from ultrasound. So I want to design a circuit to do a similar task.
I have to filter out the output to create SSB or VSB somehow.
You guys, please let me know If those high pass filters which I designed (the above pictures) cause the output to be VSB if they do not remove the toltal lower side band?
If I am can not to create a good filter for SSB then I want to create a filter to truncated the lower sideband of the dsb with carrier signal. Any suggetion?