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RF disturb. USB isolator?

Hello everyone! I hope your quarantine has been bearable and issues free. My issue is very simple: my dad is a radio amateur and now, while I’m staying with my parents, I have a lot of RF getting into my audio causing disturb I don’t know how to stop. We tried to rework some of the radio grounding and cables but nothing worked. Also testing with another device in the same spot with the same DAC I don’t get any disturb. So I guess my HP laptop is very badly shielded from RF. Should I trust USB audio isolator to solve this issue? Do you have any suggestion on what to buy? I’ve seen prices varying wildly from 15€ to 400€ and very mixed reviews, especially on the “low priced” ones (between 15 and 50€). My setup is very simple and not audiphile so I just need something that stops those RF. Thanks.

So you hear buzzing in your internal laptop speakers? or external headphone / speaker, or something else?

USB is a differential digital signal, it is not affected by RF unless you’re talking so much RF power that it’s inducing a voltage and physically damaging components.

Laptops are generally very well shielded, since they generate a lot of RF, so even ones with a plastic case generally have the case metalized internally to absorb RF, with only a few areas masked, to allow WiFi/BT reception for example.

It’s not likely a problem with grounding, but your dad’s rig could be leaking RF, maybe from a bad termination on a cable, or a homemade antenna that’s maybe not tuned as tight as it could be (or a number of other issues). How far is the transmitter, and the antenna from your computer setup?

The laptop speakers are not affected and the integrated 3.5mm jack is barely affected.

Now that you make me think about it, it makes sense. But at the same time I took another PC to the same place my laptop is at the moment and there’s no interference (a newer machine, my laptop is from 2012). So it’s not like the headphone cable is acting like an antenna either.

Yeah, they have metal shieldings inside grounded through the motherboard screws.

Well the antennas are all bought pre-made and he tuned the lenghts of all the elements of every antenna for every frequency he uses more often.
The transmitter is about 10 meters away, behind a couple walls/doors. The antennas are about 7 meters away diagonally and there is a floor and a roof (armored concrete) between me and the antenna.

Have you tested the notebook on charger or on battery? If so, did it make a difference?

USB-isolators should be cheap. The components to DIY one are in the 15€ range.

My dad was a ham as well. Outside of his equipment being tuned.

Keep audio digital until you hear it like wireless headphones.

But if a laptop is messing up audio. That is interesting. Like more data required. Is he using HF with kilo watt transmitter ?

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I’m still not sure what you’re hearing or where?

@MazeFrame It doesen’t make a difference if the laptop is plugged or not unfortunately.
Yeah, they should but I’ve seen a couple very well reviewed that cost 55€, which is a lot if you ask me.

@Marten I don’t know how much power he’s using to transmit to be honest.

@gordonthree I’m hearing buzzing of different kinds and volume of what I’m listening getting lowered. One time the buzzing was so strong that I had to rip my headphones off of my ears. It doesen’t make a difference at what volume I’m listening things at.

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The headphones are plugged into a USB DAC, or directly into the computer? Are these noise cancelling headphones, or something with bass boost (or any kind of active circuit?)

There’s no way the noise is coming in through USB, not only is the signal digital and differential, but a good USB cable is double shielded with a copper mesh and aluminum foil.

Buzzing only when the TX is active is not a ground loop. My guess is RF is getting into the DAC analog amplifier stage. Try wrapping the whole DAC with aluminum foil, it doesn’t need to be grounded to protect from RF, the Faraday effect is independent of grounding. RF could be conducted into the amplifier by the headphone cable.

Biggest question is, why is there so much RF inside your living space? Ham’s are licensed to use power, but they’re not supposed to be disrupting other electronics.

The headphones are plugged into the DAC. The same DAC plugged into another laptop placed in the same spot as where mine is now didn’t get any interference. The headphones are just plain old regulard headphones, passive.

I’ll try to wrap the DAC in tinfoil to see what happens.

It doesen’t happen with every frequency, it just happens with some. I know they’re not supposed to but it’s not like any other electronic device had any issue. Not even the speakers of my dad’s PC that’s like centimeters apart from all the equipment exhibit any kind of interference.

Same cables on both tests? I don’t see how analog noise could be getting injected into the digital side of things, which is the computer and the connection to the dac. The computers are just sending bits to the DAC not audio, no place for buzzing to sneak in there.

That’s not surprising, RF propagation is similar to voodoo. The peak of the waves could be highest a few meters or even tens of meters away from the source. 2 meter, 10 meter, 40 meter bands for example - that meter is how far apart peaks of the RF wave are.

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Same exact thing, I didn’t change anything.
I don’t have a clue either about what’s happening, AT ALL.

Yeah, I took a class during my engineering studies on telecommunications. Anyway that’s not being helpful so far.

Transmission power can be up to 500W and I confirmed with my dad that he’s using 100W now.

Does the dac get power from USB or a wall adapter? Can you power it from batteries?

Do you get buzzing in the headphones with the DAC powered up but not connected to any computer?

sorry, I’m out of ideas…

No worries, I appreciate the help.

The DAC is BUS powered, no external power. Even when the laptop is running just off of battery same things happen.