All-Band Receiver Lets You Listen to All the Radio at Once
9 comments
·January 12, 2025nickcw
vertnerd
I did this once with a rectifier, long antenna and an earpiece. In those days (50 years ago), strong AM radio stations were common, and I did indeed listen to several stations at the same time. If nothing else, it builds an appreciation for all the other junk in an AM receiver.
drpossum
"Listening to all the radio at once" is mathematically, physically, and technically impossible to do as stated on a continuous spectrum. If you have an continuous and uncountable number of possible broadcast frequencies (even in a finite range) and each has a finite bandwidth, you need an infinite amount of bandwidth.
Another way to think about it is to ask how you demodulate any given broadcast given the carrier frequency. Then when you have to allow for any other broadcast at any other frequency and then claim you can separate them with a single device and no other information. If they're not well separated in frequency, cooperatively encoded so they are separable, or possibly doing something clever with directional waves, etc you will never be able to extract both signals separately.
I'm guessing this is just effectively another software radio that will let you demodulate a countable number of sufficiently separated signals. A far cry from "all the radio".
H8crilA
You wrote a lot of words to "explain" that this sort of a circuit is supposedly impossible (no filters here, except for inherent limitations of components):
Antenna->Amplify->Rectify->Headphones
It's a classic circuit, and yes it works. Given enough power it can be even replaced with a smoking hot dog (yes, a sausage), for example when directly touching the TX antenna.
drpossum
Sure didn't and this is probably the fundamental misunderstanding the author had too. You can receive all the frequencies (this is easy and what you and the author are claiming is all you need to do). You cannot listen to all of them at once as the title suggests because it is impossible to demodulate it for all frequencies at once.
Nuance and understanding are important before you credulously say "well they say they built it so what they say must be true"
thenthenthen
It’s a classic yeah! [edit] The fact this works is because of the lack of filters or tuned circuits, its basically an amplified diode (you can even do without out it tbh)
But small correction, in this case it seems to be: Antenna > Rectify > Amp > Headphones
Right? Ofc you can add more - rf or audio - amps between the antenna and headphones. But yeah. The lm386 is pretty interesting for this use, try it out, you will surprised what you will hear (from a mess of all nearby stations all mixed together to em emitting devices in your location and possibly ghosts (:p).
fc417fc802
[dead]
molticrystal
How difficult would it be to dual use the earbuds as an antenna?
Dardinbershagit
[flagged]
> In technical terms, it’s basically a diode detector followed by a high-gain audio amplifier, which makes it safe to use without a risk of spurious harmonics or any other emissions from the (non existent) local oscillator. the down side is that the signal needs to be very strong to be detected. that means I should be physically very close the the transmitter to hear anything. in our case, I could hear the pilot, but not the ground station (pilot usually acknowledge what was communicated to them, so you can get the gist). you can also hear any other electro-magnetic energy such as atmospheric cracks, cell phones (not switched to flight mode) searching for a tower and engine roar, among others.
So this is an RF detector circuit. If you happen to be close to an AM transmitter (like an air band radio) you'll get to hear the signal.
If you are close to two AM transmitters you'll hear them both at once given that this has no tuned elements.