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Author Topic: What are some of your more interesting sources of RF?  (Read 12867 times)

Posts: 111

« on: July 24, 2013, 05:29:30 PM »

I finally got a chance to put a decent antenna up at the new QTH, and I was immediately struck with some alternating RFI on ALL the bands.  I could even disconnect the antenna, and still pick it up; faint, but, it was there.  With the antenna connected, I might as well try to listen to some AM radio while parked under some power lines...

It was an alternating noise, a higher pitch, then lower pitch, back and forth...  and it a constant time between the pitch changes, at just over a second.  I couldn't think of what in the world would be causing it.  The plasma TV was off, all my electronics were off their chargers (which had never caused issues in the old house)...  I got fed up, and went out in the yard to pull some weeds and clear my head a little...

After about 45 minutes of pulling dandelions, it hit me...  When we moved in, I immediately knew this old house was gonna need some TLC, and my 12v cordless screwdriver just wasn't gonna cut it, so I went and bought a nice Rigid 18v lithium-ion cordless tool combo set.  I had decided that the basement was a good spot for all my tools, not to mention a nice heated/cooled workspace.  That magical dandelion smacked my memory to remembering the flashing light on the charger I had hung on the wall for the tool's batteries...  The on/off cycle of the LED light fit perfect to the alternating noises.

After killing power to the charger, I came upstairs to a nice RFI free bandspace.  Completely gone was the alternating S7-S8 pitches of noise, and I am once again able to get back on the air.

So, I pose this question to the group.  What are some of your RFI sources that you've found that seemed to boggle the mind for a bit?

*edit* My apologies...  meant to have the subject read RFI instead of RF

Posts: 3

« Reply #1 on: July 30, 2013, 06:15:15 PM »

In the past several years there has been a lot of devices being built that operate
in the ultra sonic spectrum.
20 to 30 khz. and beyond.
These dvice are being used in AC motor control cicuits such as the variable speed motors found in
HVAC units operating around 27 Khz.
Over the counter low voltage halogen lighting is another application operating at 20 Khz. that puts out tremendous RFI across the full RF spectrum every 20 KHz. and can be heard  well past 30 Mhz.

More info  on these problems can be found published in the 2013 January and March issues of QST.

Larry, VE3EDY


Posts: 5

« Reply #2 on: August 03, 2013, 03:34:29 PM »

On my new Flex3000's pan-adapter I was getting some digital device noise that was spaced every 10KHz and would be present for about 5 minutes and then disappear for some time.  After attempting to time the events I presumed that some device was running for 5 minutes every hour.  Possibly some data acquisition system on my neighbors newly installed solar system?  But, the timing was not consistent.  One day when the noise was there I decided to try turning off my breakers and sure enough it was coming from my house!  After turning each breaker back on, I found the breaker labeled "refrigerator" was the culprit.  I am able to see my rig from the kitchen so I opened the frig door long enough to get the frig to start the compressor to cool.  Eureka!  It seems that when the frig turns on the compressor I get the noise.  Depending on how often we open the door, the noise may come or go less often.

Opening up the back of the frig to expose the control board, I installed snap-on ferrite beads on the wires coming from the board that carried the offending signal.  I surmised that the computer noise from the board was getting into the wire that sent some control signal to the motor solenoid.  When the relay on the board made contact, that length of wire from the board to compressor motor made a nice little antenna!  The ferrite beads totally eliminated the noise.

Posts: 281

« Reply #3 on: August 12, 2013, 01:19:50 PM »

Great find.
This is 'old news' in 2013, BUT back in the early 80s, I had some severe power line noise on my farm back in rural Ky. Using a long 6M yagi, it pointed to a pole on my property, about 500 feet from the house. Taking a portable radio tuned to a blank spot on the AM dial, it was real obvious this was the source of the noise. If you were to 'knock' on the pole with your hand just like knocking on a door, it would stop and start.
Soooo, I called the rural electric coop and they came out several times (while I was at work, natch) and said they could not duplicate the noise.
Finally, I met them at the pole. They were using the FM business radio in the truck to locate the  noise! Once I demonstrated the AM noise, a lineman stated, "I'll fix that!" Up the pole he went. Every time he would 'tighten' an electrical connection, ground wire,etc, we thought he had it fixed. On the way down the pole (climbing spikes), it would start up, again.
After a 1/2 dozen tries, out of desperation, he touched a nut that supported a metal bar that supported the wooden cross-arm. That was it. It had absolutely no connection to any conductor. It was loose and rusty. The nut would build up a charge and arc to the rusty bolt which went through the pole. Couple of turns with a big 'ole wrench and the problem was solved.

It wasn't until months later when I purchased a book on RFI, did I learn about the evils of rusty hardware.
Now days, they are 'supposed' to use double helix lock washers. These don't loosen as quickly as the regular ones. My RFI investigator said they use the correct lock washers 'sometimes'......

I'll bet that lineman is still telling that story over a couple of brews!! ha ha


Posts: 1196

« Reply #4 on: August 13, 2013, 09:50:19 AM »

Sometimes a loose/rusty connection will actually work as a diode and convert 'noise' into an rf signal.

It even has its own term.

The rusty bolt effect!

Posts: 111

« Reply #5 on: August 20, 2013, 07:36:27 PM »

Lets see, just this summer here is a list of the junk consumer electronics that used to frustrate me and wipe out my HF/6/ 2 meter and  various scanner receivers.

1. Homelite electric lawn mower charger, spurs across the entire 1.8 to 54 MHz range for over a block from the QTH
2. Black and Decker coffee maker, nice spur right on 29.6 that frequently floated around from 29. 5 to 29.7 MHz.
3. Netgear routers wall wart.
4. Numerous CFL lamps, too many to mention, these make great shooting targets BTW.
5. Phillips LED incandescent light bulb replacements, 100 to 155 MHz noise
6. Cree LED incandescent light buld beplacements, 70 to 140 MHz noise

And now for my Solution to this wonderful assortment of junk electronic noise makers.
1. Purchased a real gas lawn mower that doesn't stop when the grass is longer than 3 inches. Plus i am using the parallel batteries from the lawn mower to run a 220 MHz to 10 meter remote base with a nice solar charger.
2. An old percolator coffee maker that was found at a yard sale, sold the B&D crap coffee maker off to someone who doesn't live close to my QTH.
3. Replaced this wonder POS with a real linear supply.
4. Real edison incandescent bulbs are amazing and very quiet, Ahh now my noise floor is -134 dbm on 6 meters.
5. see # 4 above
6. See # 4 above

 RE # 1 and #'s 4 thru 6 issues, There is a lot to be said about the good old reliable gas lawn equipment and quiet edison incandescent light bulbs.
« Last Edit: August 20, 2013, 07:38:32 PM by WB8VLC » Logged

Posts: 99

« Reply #6 on: September 19, 2013, 08:56:48 PM »

When I did RFI/TVI for a power company, had entire neighborhoods flooded with noise....HF to VHF HI AND maybe higher but my test gear stopped at 225MHz. Turns out a contractor rebuilt the lines from 7600 to 20kv single phase....and did a LOT wrong....I spent 5 months of overtime cleaning up the time to look is at night...the worse offenders will ARC and you can see it from the ground...(depends on the voltage...13.2 3 phase or 7620 single phase may buzz and can be a PITA to find, while 20kv single/34.5 3phase will BURN and you can tell the difference in the noise on the radio...)...One 20KV welded a ground wire to the aluminum 3 eared bracket where the cutout was mounted...any loose hardware in the field of the 20/34.5 would get charged and then start to arc if close enough to a ground....loose staples, bolts, etc....whew, I was glad to get that done...caught the flu while out in the field and was out for 2 weeks.....FIRST thing is make sure its NOT IN YOUR HOME.....if it is, you have to fix it...anything before the meeting is the power company's problems....and they must fix it...ask nice and try to get cooperation...if they refuse, then go to the state PSC/PUC.......then the FCC....may take a while but it can be fixed if they have people who know what they are doing.

Posts: 188

« Reply #7 on: September 22, 2013, 12:17:23 PM »

I had this intermittent low level click I would hear on receive on an HF receiver. It was about 2 clicks per second. Some days it would be there, others it was not.

At this building I once lived in, I walked outside one day to inspect my cables coming into the house and the grounding apparatus there. This receiver and station was located right on the other side of this outside wall. While making this routine inspection, I noticed a tube coming out of the foundation wall. Water was dripping from it. It was a drain for a dehumidifier. The water was dripping onto a large stone sitting at the base of the foundation. The rate ... well ... about two drips per second.

I said to myself, "No way!". I ran in the house and turned on the receiver. The clicks were there. So I turned up the volume and went back outside. Placing my hand as to catch the drips, the clicking ceased. I couldn't believe it. I'm still at a loss as to the cause. I have theorized the force of a falling drop of water was enough as to cause a localized pressure change in the stone. And given the particular chemical composition of the stone and the pressure change, possibly causing a miniscule piezoelectric discharge. Otherwise, I have no idea what created that phenomenon.

I had dealt with that click for about three years before I noticed the dripping water.

So, is that an interesting source of RFI or what!

John, W2WDX
« Last Edit: September 22, 2013, 12:29:36 PM by W2WDX » Logged


Posts: 567

« Reply #8 on: September 28, 2013, 08:25:15 PM »

...on my neighbors newly installed solar system?

Your neighbor owns a solar system?  Eat your heart out, Donald Trump!

Posts: 274

« Reply #9 on: November 05, 2013, 06:43:13 PM »

......There is a lot to be said about ....quiet edison incandescent light bulbs.
True but I cannot buy them anymore around here.
This past September, I bought a Philips Halogen replacement-bulb for my garage-opener-light; it did not last 2 months but the incandescent bulb lasted for years.
So much for progress. Embarrassed
I truly hate having to change that bulb; I'm on a step-ladder and the plastic-guard is so darn hard to remove.
I realize that has nothing to do with RFI; the reason I looked at this thread is for background towards a class that I have to give in February on RFI to our club.
73 Jerry KM3K

Posts: 150

« Reply #10 on: November 07, 2013, 06:44:00 AM »

The swept local oscillator of my Systron-Donner spectrum analyzer.  I hooked it up to the cable system in our house to view RCN's signals and promptly knocked out the XYL's tv -- while she was watching the finals of "American Idol".

Worst than getting reamed out by the FCC!


Posts: 1368

« Reply #11 on: November 07, 2013, 12:15:41 PM »

Packing tape from the shipping department. Everytime they were sealing up boxes it made the spec analyzer go crazy.

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama

Posts: 133

« Reply #12 on: November 07, 2013, 03:50:09 PM »

this was the "more interesting" rfi amongst all the crap I get here. This was last year. That neighbor still reluctantly waves hello whenever I'm outside Grin

Posts: 5

« Reply #13 on: November 08, 2013, 08:36:56 PM »

My RFI issue was with the LED TV downstairs. Every time I TX on 10-20m, the AT&T U-Verse would lose signal.

I had a tech come out and we took the TV and DVR box upstairs where the gateway was, along with my shack.

I TX on 14.070 at 20w (testing pattern in DM780) and no RFI issue! So, we went up in the attic and found that the coax run from the splitter up there to the jack the TV uses was several sets of 6' of coax then a barrel, repeat...

The tech disconnected it, ran a brand new CAT5 cable from the NID outside to the jack and I haven't had a problem since on any band, mode or power output. It is REALLY nice for everyone in my house now.
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