Spooky Wireless Reception of EEVBlog

[srruhl3701]

Hi all,
I recently discovered EEVBlog. I've been binging on the playlist. Today I received a cheap TecSun AM/FM/SW radio. As expected, there is a lot of noise when sitting by my laptop watching Dave.

I looked up a program guide and found the Beeb was broadcasting on 12.95 MHz. The last scale marking on that band is 12.05. I cranked to the stop and got reception. The voice sounded more Aussie than Brit. Then I tuned better and it was Dave. I knew he was expanding everywhere, but SW?

I turned down the radio and realized it was in sync with Dave's Rev C power supply video which I was rewatching. It's getting spooky now. I turned the dial and found Dave again somewhere around 11 MHz too. I turned the radio off then.

It's a basic Dell laptop of 2011 vintage, with WiFi. I have external speakers, but they are not wireless. The audio comes from the Line Out jack. They use USB just for power.

The spooky wireless audio happens at a few feet from the laptop. From the multiple receptions, I figure it must be an image frequency thing, but where is it coming from. I guess I just grab the scope and take a look for RF on the audio out and uSB.

[Brumby]

Dave ..... are you experimenting with something we don't know about?   

[aargee]

It has to be this...
https://www.amazon.com/Spirit-Ghost-Hunting-Equipment-Radio/dp/B00NABGFSM/ref=sr_1_1?dchild=1&keywords=Spirit+Box&qid=1593661640&sr=8-1
 

[james_s]

It's probably harmonics of the class D audio amplifier, or the switching regulator that powers the audio IC.

A few years ago I was playing with a chiptunes player on one of my FPGA boards and found that an AM radio could pick up the music from several feet away.

[srruhl3701]

Thanks, that has to be it. The amp has to be in the in line volume control. There's not much room in there for anything but Class D.

[Brumby]

It's probably harmonics of the class D audio amplifier, or the switching regulator that powers the audio IC.

A few years ago I was playing with a chiptunes player on one of my FPGA boards and found that an AM radio could pick up the music from several feet away.

This has been done a very long time ago....

https://www.youtube.com/watch?v=EPk8MVEmiTI&feature=youtu.be

I even worked out the mechanical timing of print hammers on the IBM 3203 line printer and got it to play "Whistle while you work" and "We wish you a Merry Christmas".  The IBM field engineer - Roger - smiled.  (He never smiled!)

[srruhl3701]

It's the USB powered speakers. I probed around with a small inductor across my probe. EM emissions correlate with volume levels.

I've attached a few screen shots from my exploration, The audio is a 1kHz tone courtesy of You Tube at 50% volume set on the PC. At higher volume levels, I saw close to 700 mV P-P. No wonder a receiver expecting uVs was picking it up everywhere.

BTW: EEVblog #1178 - Build a $10 DIY EMC Probe was what I was watching as I decided to scope it out.

[edy]

Today I received a cheap TecSun AM/FM/SW radio. As expected, there is a lot of noise when sitting by my laptop watching Dave.

I have the Tecsun PL-310ET, is that what you have? I haven't experienced picking up anything from local EMC (at least not recognizable audio but probably other buzzing from lights, chargers, etc). I find when I plug it into the wall to charge the internal NiMH batteries the radio becomes practically unusable due to my crappy USB charger. I can only run it on batteries.... unless I can find a better USB wall-wart.

Sometimes using the ET mode it programs a bunch of stations but will "mirror" the same station to multiple frequencies, especially one with a strong signal. I guess it is picking up the "harmonics". Not sure if this is a phenomenon of the DSP workings or if more "analog" type radios tend to do the same.