Timeline for AM Modulator Mixer Circuit
Current License: CC BY-SA 4.0
14 events
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| Jul 26, 2018 at 17:52 | history | edited | user6972 | CC BY-SA 4.0 |
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| Jul 26, 2018 at 17:36 | comment | added | user6972 | @ChrisStratton my suggestion is IF it works it's direct coupling into the receiver (no modulation or RF). It's very possible and I've seen it happen with AM receivers. I don't think the down voters are understanding this aspect. | |
| Jun 28, 2018 at 22:01 | comment | added | Chris Stratton | This answer is simply wrong. Linear behavior does not create a radio signal, and as Olin points out, and audio frequency one won't couple through radio signals. If the circuit in the question works (and it can probably be adjusted to do so to a degree), it works by exploiting non-linearities to perform mixing. Essentially any allegedly linear circuit has these, especially at the extremes, so it's quite possible to steer the situation to the point where the non-linearity becomes noticeable. | |
| Jul 3, 2013 at 0:14 | comment | added | user6972 | @OlinLathrop I added a bit more of an explanation for you. | |
| Jul 3, 2013 at 0:13 | history | edited | user6972 | CC BY-SA 3.0 |
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| Jul 1, 2013 at 0:13 | comment | added | user6972 | @OlinLathrop I understand that quite well. I don't think you should rule out the idea that it won't work. I could make a simple AM receiver that would accidentally pick up feed though assuming the TX signal is strong (even into a non-resonate tx antenna) and the TX/RX are right next to each other. The question was how could this work, right? Not how should this be designed to work. | |
| Jun 29, 2013 at 13:59 | comment | added | Olin Lathrop | You are missing the point that the 10 kHz audio signal won't propagate off the antenna. From the point of view of RF that is basically DC, and DC is lost in radio transmissions. The only way your scheme could work is with a direct wire connection that can carry the low frequencies, but that's not what is being talked about here. Note the output of the second opamp clearly going into a 100 pF cap and antenna. 10 kHz simply isn't going to make it to any receiving antenna, even if the receiving tuner doesn't filter it out somehow. Think about your waveform in frequency space. | |
| Jun 28, 2013 at 23:54 | comment | added | user6972 | I just went to the link to see what was there but my cell data connection is too poor to even begin viewing it. If he's using a similar crappy homemade detector then he's probably not getting much filtering across the whole band. Thanks for the down vote anyway. | |
| Jun 28, 2013 at 23:39 | comment | added | user6972 | @OlinLathrop I agree with you, however it depends on how the TX/RX system is setup in the demonstration because with just a weak bandpass (used in the graph I made above) the AC signal comes through enough to be detected. I understand it goes against the grain, but I'm just looking at how it might be made to work. It's outside the box. | |
| Jun 28, 2013 at 19:32 | comment | added | Olin Lathrop | No, that's not how AM demodulation works. Remember that a AM receiver starts with a very narrow band filter. The modulation signal in your first plot is just added to the carrier and will be rejected by this filter. Think of it in frequency space. Your whole premise is just plain wrong. Another way to think of this is that the "diode detector" you mention won't ever see the signal in the first plot. | |
| Jun 28, 2013 at 18:31 | comment | added | user6972 | It would be interesting to see what the pseudo-am signal looks like in the real circuit. Is the audio really shutting off the carrier due to the bias conditions as Andy suggests? | |
| Jun 28, 2013 at 18:25 | history | edited | user6972 | CC BY-SA 3.0 |
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| Jun 28, 2013 at 18:19 | history | edited | user6972 | CC BY-SA 3.0 |
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| Jun 28, 2013 at 18:03 | history | answered | user6972 | CC BY-SA 3.0 |