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Author Topic: Noise floor high on 40?  (Read 1088 times)
WB4IUY
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« on: January 27, 2009, 05:51:56 PM »

I'm wondering if something has gone wrong in my general area, or if it's propogation tonight... I have a somewhat selective directional antenna on 40. It has a broad forward lobe, and I can select south, northeast, and northwest. I've been running this since around '93. Tonight, I'm seeing HUGE wideband noise on 40m, with the due south lobe being the most quiet. Just wondering if anyone else is seeing this...


Dave WB4IUY

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WB4IUY
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« Reply #1 on: January 27, 2009, 06:28:18 PM »

Now that I've dug a little deeper... I'm hearing a pronounced peak in the interference approximately every 60khz, from 160m through 10m. It's very strong on the lower banks (160-40), and begins to diminish a bit on 20, 15, and is fairly low by the time I get to 10 meters. It seems to be coming from the northwest from my QTH, and is generally trashing my use of the low bands.

Anyone else had this sort of problem?

Dave WB4IUY
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WV4L
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« Reply #2 on: January 28, 2009, 08:32:40 AM »

Yes Dave.
This has had me perplexed for over a month now. There is no consistency of when the noise comes around. At first I thought it might be localized to my area but I have overheard others in different areas make mention of this. When I have it, it is a good S7 level hear at my location and it makes it impossible to obviously hear DX stations that would otherwise be a good copy.

Wayne C.
WV4L
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KY6R
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« Reply #3 on: January 28, 2009, 09:18:18 AM »

40M has been noisy on the West Coast as well. There have been few days where we get the EU LP signals that we have in the past. December, January, and half of February used to be great on 40M morning greyline.

However, 160M and to some extent, 80M have been better than anytime I can remember since 2001, and 30M has shown some good Eu AM greyline.
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WB4IUY
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« Reply #4 on: January 28, 2009, 03:06:58 PM »

Thanks for the reply, Wayne. I had the local EMC come out and fix problems on 4 poles, and that helped.

I have a cluster of 3 spurs that appear every 60khz, from below the AM broadcast band, through 10 meters (strongest from 160-20). The spurs have a stronger center frequency, and a spur on either side of it +/- 6khz of lesser amplitude. I've been all over the area and can't find it...still looking.

The wideband noise brings the baseline on the IC-756 scope up quite a bit from the NW (around 310 or so degrees), and seems to be constant now, all day, all night. Still looking for that one, too.

Dave WB4IUY
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WV4L
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« Reply #5 on: January 29, 2009, 01:10:59 PM »

Turned on the rig this morning and it was a solid S9 across the bands no spurs no drops, just grinding static!
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WB4IUY
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« Reply #6 on: January 29, 2009, 04:08:29 PM »

This is kind of a cross post, I also had it in the RFI forum...but...

Boy, I feel like a dummy-de-dum-dum... After the powerline noise was corrected, I had the wideband noise w/spurs I mentioned previously I could rotate my yagis, and find it at about 330 degrees. Yet, when I loaded my Escape wih receiving gear and cruised around, I couldn't find it. I set up some portable gear, and walked NW from my QTH, still couldn't find it...couldn't even HEAR it!  

I came back to the shack, and noticed I could hear it around my home. I traced it back to a new computer, right in my own shack! I failed to follow the first rule of turning the house off first, to determine if it was local. When I killed the computer, it was beautifully quiet on HF!

It was a crappy switch-mode supply in the PC. I put torroids on the power cord and nearly killed the noise. Gonna work on it more, when I get over feeling so stupid, hehehehehe...

The good part of this was the great service I got from Wake EMC here in NC. Those guys were all over the powerline noise in my area, in short order. They fixed 4 poles with problems, and it's as quiet as a mouse out there, now. All well that ends well...

Dave WB4IUY
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N4KZ
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« Reply #7 on: January 31, 2009, 12:12:53 PM »

I had nearly the same identical experience with a computer, an eMachine desktop in my wife's office, that was causing a strong, constant noise across 80, 40, 30, 20, 17 and 15 meters. But it was quite awhile before I realized the noise was from inside my own home. I had called the local electric utility to report power line noise that peaked from the west when I turned my beam. They were very cooperative and replaced two transformers in the immediate area and also found a bad ground. But when they said they had eliminated the noise and I was still hearing it, I took my FT-817 around the neighborhood. But I didn't hear a peep. I was perplexed!

Then I walked in the house with my FT-817 and the noise suddenly got strong. I walked around the house and found the culprit in the office. Boy, was I embarrassed that I had assumed the noise was coming from the power lines when it was really from inside my own house. But we'd had that computer for 5 years without any noise but suddenly it went bonkers. I would assume it was the power supply. But I still had a strong pulsing noise on 30 meters and tracked that down to a cordless telephone -- also in the office. We'd had that phone for several years but suddenly the wall wart started pumping out horrible noise on 30 meters. Unplugged it and the noise went away and suddenly I have no noise on any band at any time. Months and months of frustration and reduced operating time because it was hard to hear weak signals were suddenly wiped away.

The lesson to this story - in my case - never assume the noise is from an outside source until you have thoroughly checked your own home and electronic devices. I think I have learned my lesson this time!

73, Dave, N4KZ
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W5WSS
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« Reply #8 on: January 31, 2009, 01:28:16 PM »

Hello Dave Wb4iuy, I have noticed this also. Does yours sweep back and forth or does it just stay still? Mine moves around so I perhaps prematurely concluded the noise to be local qrn from I guessed from the large catv system 50' from my antenna. I hear the same identical interference on all bands and on different rigs and antennas 73
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W5WSS
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« Reply #9 on: January 31, 2009, 01:52:13 PM »

I forgot to mention that I did look here at home first and even turned off the main power at the service panel still when using battery power. So pc's at my house check out ok. Could be from the neighbors.
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WE0Z
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« Reply #10 on: February 01, 2009, 04:01:11 AM »

I had same problem and discovered a very trashy power supply in one of my 7 desktop  computers. I bought a different brand of p/s for it and now have a quiet band.
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