Timeline for AM modulation stage for small transmitter
Current License: CC BY-SA 4.0
17 events
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| Mar 22, 2020 at 14:33 | comment | added | user136077 | Just noticed that you can detect with a radio something you call "static" If you receive the carrier and there's AM modulation with audible frequency (=say 0,5...1 kHz, at least below 5kHz) you should hear it, too. Otherwise you receive something else. | |
| Mar 22, 2020 at 14:29 | history | edited | user136077 | CC BY-SA 4.0 |
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| Mar 22, 2020 at 7:48 | comment | added | user136077 | I mean connecting the signal GND with a capacitor to real ground. Examples: waterpipe, mains protective ground, a built separate ground wire or "counterweight", that's a a quite long horizontal cable well away from the antenna. All wires of these are a part of radiating system. Using it in a house where live other people can be harmful because you can force them to take your broadcasting via their non-selective devices such as music players or your transmitter generates harmonics just on their receiving frequencies. Be careful! | |
| Mar 22, 2020 at 1:11 | comment | added | Riley | what a good way to ground the system? Currently, I am using a bench supply negative terminal as ground. | |
| Mar 22, 2020 at 0:52 | comment | added | user136077 | 4Vpp should be receivable if you have an antenna and ground. For 1250kHz the antenna must be quite big. 60 meters high would be optimal, but try at first 1 or 2 meters. Ground is also needed. | |
| Mar 22, 2020 at 0:33 | comment | added | Riley | Would you expect that if I see the wave (4 Vpp 1250kHz) on my oscilloscope I should be able to receive it? I currently have the receiver right next to the transmitter and all I hear is static. Also no need to worry, I am operating well below the power limit in my country ( I can't even broadcast a few inches). | |
| Mar 22, 2020 at 0:23 | comment | added | user136077 | Linear amp should be connected to RF out in the right edge. BEWARE: The oscillator with its coil and modulator should be in metal shield to avoid making an incredibly unpredictable complex oscillating system. Another thing: Do not make any radio broadcastings without a legal license which is valid in your country. There's many jails waiting new inhabitants. I wrote this because I do not want to be one as an assistant. | |
| Mar 22, 2020 at 0:14 | comment | added | Riley | if I add a linear amp, should it go after the oscillator, where you have labeled RF out? | |
| Mar 22, 2020 at 0:07 | vote | accept | Riley | ||
| Mar 22, 2020 at 0:06 | comment | added | Riley | Perfect, that is now modulating the oscillations. Now I have about a 4 Vpp AM modulated wave. I'm struggling now to pick it up on a receiver. Any suggestions? Should I put an amp on the output of the oscillator? | |
| Mar 21, 2020 at 23:54 | history | edited | user136077 | CC BY-SA 4.0 |
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| Mar 21, 2020 at 23:13 | comment | added | user136077 | No. Feed your oscillator with DC from an emitter follower which has voltage divider making good DC to the base. Connect the audio to the base with a capacitor => you'll have swinging DC operating voltage for your oscillator. Have a few hundred pF capacitor from the emitter to GND, too in parallel with the oscillator. | |
| Mar 21, 2020 at 23:01 | comment | added | Riley | I built the audio amp and the Colpitts oscillator my self, so they are very weak. I tried driving the oscillator from the amp but I think it is too weak. It sounds to me like I had the right idea with the first circuit, I was actually tinkering around with it and got something like AM out. Would you suggest using the circuit I originally designed? | |
| Mar 21, 2020 at 22:47 | history | edited | user136077 | CC BY-SA 4.0 |
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| Mar 21, 2020 at 22:37 | history | edited | user136077 | CC BY-SA 4.0 |
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| Mar 21, 2020 at 21:50 | history | edited | user136077 | CC BY-SA 4.0 |
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| Mar 21, 2020 at 21:44 | history | answered | user136077 | CC BY-SA 4.0 |