Bad Power Supply RFI

[E-Man]

Picture 1- Red lines shows RFI emitted from Bad Power Supply

Picture 2- RFI from PS with Antenna Disconnected

Picture 3- Screen Shot with Bad Power Supply Disconnected

Picture 4- Bad Power Supply from Android Smart Box shipped from China similar to:

Android TV Box CS838 Android 4 2 Mini PC Dual Core 1g 4G HD Hardware Decoding | eBay

The RFI from this PS showed up across the Bands, and really took the fun out of using my SDR-IQ.

I was able to identify the PS, by using my portable Sangean 909X by tuning to the frequency of the noise and making contact with my many PS's with the Antenna of the 909X. When I made contact with the pictured PS the noise made it clear that I had identified the culprit.

Many thanks to BruceB for tech support, and Nickcarr for helping me track down the bad PS.

Happy Holidays Everyone!

 

[SCPD]

E, you should go around the house and turn on anything electronic or electrical -- in particular, lamps, dimmer switches, appliances, etc. Take the 909x with you and go room by room. You'll likely be shocked at what you find.

From my experience: older electric blankets, garage door openers, dimmer switches, touch lamps, door bell transformers, halogen lamps, new CFL bulbs (these things are garbage!) -- not too mention anything electronic that uses AC mains power.

In your above case, of the cheap switching mode power supply, it would be interesting to crack that open and look at the electronics. Probably zero filtering elements in there...

One other point: multiple noise generators on a the same circuit can create essentially a large transmitter using the AC wiring as an antenna. Of course, this just amplifies the effect and makes life hell for any SWL'er.

 

[nanZor]

Along with the proliferation of 5V devices, even using DC power does not guarantee a quiet supply as many of the mobile dc usb adapters are switching and not linearly regulated anymore.

Found this out the hard way a few years ago running solar with a mobile 12v-6v dc adapter. Switching noise which I didn't immediately suspect threw me for a loop trying to find it! Sure enough, no linear regulator in it either, but a broadband noise emitting switching device.

These days, I have to either dig hard or just build my own classic 3-pin linear regulator (LM xxxx) supplies for the low voltage stuff.

 

[SCPD]

Along with the proliferation of 5V devices, even using DC power does not guarantee a quiet supply as many of the mobile dc usb adapters are switching and not linearly regulated anymore.

Technically those devices are still run off AC. Anything that converts AC to DC can be a potential noise source if it doesn't have the proper filtering elements.

The only real DC power source is from batteries (or solar panels.)

 

[fleef]

Speaking of noise generators

I had a mystery noise that was terrible. I couldn't figure it out but I knew it was close by the way it sounded. I went around the house with a portable AM radio (didn't have batt powered SW then) on 1700kHz or so- found the source of the BBBBZZZZZZ coming from an old, hot wired light outlet above my kitchen sink (that was connected to a nonworking fluorescent *yyechch* lamp) it buzzed even with the wall switch OFF and the power to the non-working lamp on the OFF position. What a piece of junk! I don't know enough about electronics to figure out what was going on, but whatever it was the HOA maintenance man took care of it. Then I found another hall light that is noisy, but only when powered on. I have incandescent bulb in it too, makes no difference.

By the way- as of Jan 01st 2014 NO MORE INCANDESCENT BULBS WILL BE IMPORTED, MADE OR SOLD IN THE USA.

This was a tiny article on MSN and I haven't heard a peep on the TV news about it. Might want to stock up on regular light bulbs, I hit the mad house of Walmart to day and got a load of them.