Sometimes the old tricks are the best. [Kevin] learned an old trick about using a ‘scope to sniff RF noise and pays it forward by sharing it in a recent video. He uses an oscilloscope. But does he need some special probe setup? Nope. He quickly makes a little RF pickup probe, and if you have a ‘scope, we’re pretty sure you can make one in a few seconds, too.
Of course, you can get probes made for that, and there are advantages to using them. But the quick trick of quickly and non-destructively modifying the existing probe to pick up RF means you always have a way to make these measurements.
The first thing he probes is a small power supply that is broadcasting inadvertently at 60 kHz. The power supply was charging a bug zapper and, as you might expect, the bug zapper throws out a lot of noise on the radio bands.
If you have an FFT feature on your scope, that is often useful, too, as you can see the results of several interfering signals mixing together. Hunting down interference is a basic skill if you work with radio, and it’s useful even if you don’t.
In the early 1970’s, my computer repair toolkit included a small 6-transistor radio. Held near the backplane of the refrigerator sized computer, I could pinpoint bad cards as the machine was powered-on … different locations would “play” a different tune. One soon learned to identify the music of a correctly working machine.
That’s a pretty cool use of the technology. My son and I still use a little portable radio set to am to look for interesting power signals. Our favorite so far is a little plasma globe that we have.
Can sometimes be fun to flip on the AM radio while going through an automatic carwash.
Amazing!
Ah yes, the antenna ground lead. It works well for picking up noise, but makes a terrible ground when you’re actually trying to measure anything.
the “RF probe” is just a regular oscilloscope probe wth the ground lead clipped directly to the probe lead.
which is about what i expected and so easy to describe in text
One of the first circuit I built, back in the 80s, was an RF sniffer.
FET high impedance front end (MPF106?) and LM380 audio amp, IIRC.
Thanks for the memory flashback.
Yoink. I’ll be hanging onto that little pointer. I also often use a regular ole LED on the end of scope probe when diagnosing high speed lights in machine vision applications. Not the best sensor for the job but there’s always a few in my flight case. Doesn’t need a voltage source but wants pretty intense light. A little photocell would be better.
Very inspiring. I will try to hang LED onto mic input on notebook with some appropriate audio software. And revive an old AM radio from deepness of garage shelves.
The waveform at the end looks like the screen signal itself. You may be able to see a difference by showing different content on the screen.
May I be so bold as to suggest a piece of semi-rigid coax bent and soldered to the shield to form H-field probes? Different diameters have different ranges.
Used semi-rigid cables are cheap.