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Comment by joeyspn | Hacker News Reader

My neighbour (next door) is a radio aficionado and a thing that worries me is that sometimes when I'm with the headphones or speakers connected to the computer, I can hear him speaking... Does anyone knows how is this possible if the macbook does not have receiver? this has me puzzled...

I find the amateur radio somewhat interesting, but on the dev level. I was about to buy a HackRf, and I'll probably do it when I have more free time...

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Any sufficiently long wire is an antenna. If your neighbor is using amplitude modulation, there isn't much of a difference between the signals your macbook produces on its end and the signals his radio waves induce directly into the wire.

EDIT: this is why differential signalling [1] over twisted pair is used for ethernet, USB, etc. Otherwise the radio waves already present everywhere would garble the signal for any non-trivial length of cable.

1. https://en.wikipedia.org/wiki/Differential_signaling

So if you are picking him up, go ask him about it. He'll be able to sort out what's going on and fix it. As a long time ham I've had two complaints, both about cheap cordless phones.

And I had a neighbor that had a microwave oven that splattered RF everywhere. It was older and cheaply made. I poked at it to see if there was an easy fix. Nope, so I just bought them a new one.

Hams work very hard to not be a radio nuisance.

If it's audible in headphones I suspect that the fix would involve soldering HF bypass capacitors at the inputs of the onboard headphone amplifier. Doable, but will the owner agree to this? Well... ;)

He's likely breaking a FCC anti-interference law (with older equipment probably). Radio waves have harmonics like instruments do, sort of. So you repeat your transmission quieter and quieter on some surrounding frequency.

You can hear it because your headphone wires will pick up wavelengths about the same length (ever heard of people making AM radios with wire and a tin can?). My understanding and I hope I can be corrected if wrong is that this only will work for FM transmissions.

I've heard the best thing to do in these situations is to politely inform your neighbor of the situation and to investigate a solution. Probably some filter on his transmitter would do the trick. But I'm sure if he's serious about radio, he'll have a grand time fixing it...

As far as I know, Part 15 Class B devices are required to accept interference from licensed transmitters that are operating within FCC limits.

A useful rule of thumb:

If a non-radio device is picking up radio signals it can never be the Transmitter which is at fault.

It must be RF breakthrough caused by bad (eg cheap) design in the device.

Source: Retired EMC engineer.

P.S. I've never heard of people building an AM radio with a wire and a tin can. And if it were possible, any fault would be with the poor receiver not the transmitter.

A tin can wouldn't be the best choice, but almost any cylinder would work. I've seen crystal sets using Oatmeal boxes, water bottles, etc. I've built them using wood 2" square and about 6" long. Some wire, a crystal or other diode, and a capacitor and you can get any of the clear channel stations.

(Capacitor can be made out of foil and paper, crystal out of the graphite from a pencil and a razor blade. The radio pioneers were pretty inventive. Google early crystal radio receivers.)

"..any fault would be with the poor receiver .." is correct, but if you took the time to build your own crystal set, definitely go see the ham next door, he most likely has the parts in his component stash to add some better RF selection/rejection to your radio.

Just like most of you like to tinker with code, we like to tinker with radios.

Not necessarily. I have seen one crappy amplifier which picked up commercial radio broadcasts. Many audio devices pick up cellphones. All these signals probably are within spec.

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