Digging Out New Shack RFI
David F. Doler Jr. (WA3YAY)
on
December 4, 2006
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In 1975 when I was first licensed, there was a fraction of the potential noise sources that there are today to deal with.
I've recently starting getting active again and purchased a nice used TS-440 from a fellow ham.
I wondered what I could expect when I brought the thing home, so I got my little Radio Shack DX-398 receiver, tuned to WWV on 10.000MZ I went on a noise treasure hunt.
See if you agree with my approach to tracking down all of the local sources of my buzzes, pops and growls.
First I shut down all of computer, audio-video equipment, washer, dryer and anything else I could find. 10 MHz was far quieter, but as I walked around the house I found more than I expected.
Now this is no surprise to anyone here on eHam, but the dimmer in the dinning room was just buzzing away and didn't stop when I turned it off. That's got to go. Then the automatic light in the backyard spoke up. That got to go too.
While I was working here the piezo gas lighter in the heater went on. Well, can't have a cold house. Water heater too. Ditto.
Now I had a baseline. I knew what little devices I couldn't shut off completely - yet. But as I did more walking around the house, DX-398 in hand, WWV ticking away, I noticed that as got I closer to my new Samsung TV, which was turned off, the noise level went up greatly. Now I should know this, but being turned off doesn't mean much to most modern appliances. I pulled the plug on the TV - noise drop. I pulled the plug on the DVD player - big noise drop (what's that thing doing?). Surprisingly pulling the plug on the cable box didn't mean much to the DX-398. -- Now off to the computer. I climbed behind the thing and pulled the plug. What a nice sound WWV had now!
So here I was with just about all of my electronic appliances not only turned off, but actually yanked from the AC mains, and except for some occasional pops and transient buzzes, things were really quiet!
I restored to life each of the devices one at a time, carefully noting the new sounds then added to the mix, each slowly drowning out WWV. As everything came back to life I wondered just how I could get everything to live happily with my new TS-440.
So here are the questions: How indeed? Would wrapping the AC cords of everything in a ferrite core thing help? Grounding everything? Unplugging all but the essentials when I'm in the shack?
So I am writing this to get a dialog going. Except for the really tough things to fix -- funky new car electronics, buzzing line pole transformers that the electric company ignores and maybe the hair dryer from next door, what is the best way to nix RFI noise?
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Digging Out New Shack RFI
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by KY1V on December 4, 2006
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Great Questions, however, before you spend a lot of time getting rid of all the transient noises generated by all those devices, ask yourself this...
What was the impact on my TS-440 after turning off those devices?
I am willing to bet that much of that noise you pick up on the portable receiver is never making it to your radio. Some will, but why fix what isn't broken?
Solve only those that are impacting your tranceiver in it's normal operating position and mission accomplished!
David ~ KY1V
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RE: Digging Out New Shack RFI
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by WX1F on December 4, 2006
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I agree with KY1V. My 746Pro screens out everything..so if I have a yen to tune around in general coverage, I use it, instead of the little Sangean ATS 505, which is now reserved for RFI witch hunts and shower stall background music.
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RE: Digging Out New Shack RFI
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by AD5X on December 4, 2006
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A little distance from the noise sources really helps. While I can pick up a lot of noise from electronic things in the house using my IC-703 as a portable receiver, once I connect the radio to my chimney mounted rotatable dipole or to my vertical in the back yard, the noise effectively disappears. The only problem I had was from my powered subwoofer (very bad 10 MHz noise), which I was able to cure with ferrites on the AC cord.
Phil - AD5X
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RE: Digging Out New Shack RFI
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by K2PDJ on December 4, 2006
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I agree with everything that has been said. Take a look at the real world and see if there is any left over electronic interference with the rig hooked up and go from there. My approach was to take to heart the balanced antenna tuner described in a April 2002 qst article. Getting a truly balanced line out of the shack and to the antenna seems to cure a large percentage of household noise that is picked up when the line is not balanced. Btw I run two computers. One for a keyboard at the operating position and the other about six feet away without a significant problems. I do have a slight buzz at 7.028 that is s 1-2 without filtering. That's all.
Bruce Bennett k2pdj
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RE: Digging Out New Shack RFI
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by K3AN on December 4, 2006
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Get your antenna(s) as far from the house as practicable. Vertical distance is best (go up), because the incoming signals you want to hear will be stronger. That will improve your S/N ratio.
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RE: Digging Out New Shack RFI
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by K4DXA on December 4, 2006
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I did the same thing you did but as part of the ARRL RFI course. They guys are right on. With a decent antenna you will not hear most of those things on a good hf rig. I only have outside interferance from power lines and the cable co. Both of which the locals have worked on to fix and mostly sucsessful.
If your antenna is real close to the house(not a good idea) you may hear stuff from computers, monitors etc.
When you have something bothering the hf rig then track it down with the portable radio.
Have fun getting back on. Ken K4DXA OO Charlotte,NC
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Digging Out New Shack RFI
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by W0FEN on December 4, 2006
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Remember that there are two ways to have interference reach your radio. They are: radiated and conducted. All of your tests were on radiated interference. The inverse square law of radiation works very well for this type. As mentioned by another commenter maximum distance between the two devices will drop the noise tremendously. Conducted noise is a little bit more sneaky. There are two modes of this as well. The most common is common mode interference but there is also individual wire interference. Common mode is where both wires commonly have the interference on them. Remember it takes two wires for a complete circuit. The individual wires can have different noises on them as well. A good isolation transformer for your radio will eliminate most of the conducted noises. Shielding is one solution to radiated noise but distance can work was well.
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RE: Digging Out New Shack RFI
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by K8MHZ on December 4, 2006
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I feel your pain...
I have so much RFI I have a database for the noises. They are listed by frequency and type of noise. If I am on a certain frequency that has noise the first thing I do is check the database and see what needs to be turned off. I also have breaker numbers listed if I know them.
I have problems with my computer, monitor, CATV amp, Sanyo TV, and both surveillance cameras here at the house.
I also have had problems with bad CATV devices in neighbors homes up to 1/8 of a mile away and had to use RDF equipment to help the CATV techs pin down the source.
I now have a problem coming from another neighbor's home on an intermittent basis that comes in as S9 60 Hz hum. They live about 500 feet from me. Fortunately my noise blanker takes care of it.
When I am looking for the source of noises the first thing I do is turn off our main breaker and run the rig off battery power. This will tell me if the source is in our house. Then I turn the main back on and shut off each breaker one by one. This will tell me which circuit the source is powered from and then I go from there.
I use a small SW receiver as a probe and that works well, but not as good as a wide coverage handheld communications receiver.
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RE: Digging Out New Shack RFI
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by N3OX on December 4, 2006
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A quick and dirty check if you have bothersome RFI is to run your main station RX on batteries and pull your house's main breaker.
If the noise drops off, it's in your house. If not, it's not! If it's in your house, you can shut down single breakers to track it down. This has the advantage of telling you in minutes where to look for the noise.
A little aside from the main topic. Regarding powerline or other utility-generated noise, have you called the power company? Sometimes they just don't know. It sounds like you've probably informed them if you feel like they're ignoring the problem, but if you haven't, you might call them up. I've been very lucky here. When I moved in, I had debilitating power line noise, but Pepco's RFI resolution policy is very good, and they employ Mike, K3RFI, who also runs a consulting firm called RFI Services which does RFI location, mitigation, training, etc. He showed up in a truck bristling with antennas; HF mobile whips, a couple of what looked like doppler DF setups for VHF, all sorts of VHF antennas, and the best of all, a VHF log periodic mounted on a rotatable mast down through the truck's cab. Faaantastic.
It seems like Philadelphia's PECO is on the list of RFI Services' clients. If you do have utility RFI and you haven't called them, do it. Some utilities have a pretty lax policy about such things, but when it comes down to it, power line noise means arcing, and arcing means that something's about to fail, so the smart power companies really do want to know.
73,
Dan
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RE: Digging Out New Shack RFI
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by N3OX on December 4, 2006
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Mark, looks like you beat me for the pull the main breaker post ;-)
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RE: Digging Out New Shack RFI
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by K8MHZ on December 4, 2006
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Don't forget to turn off all the UPSs in the house when you turn off the main. Not only will they keep connected devices powered up when the main is off some of them generate noise on their own.
On another note, when I was first starting to track down one of the noises coming from my neighbor's house I shut down the main and still heard the noise. It was eminating from the ground wiring and anything touching it. A grounded metal frame on one of our lights would blast my little SW reciever with noise when the antenna was placed a couple inches from it.
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RE: Digging Out New Shack RFI
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by NI0C on December 4, 2006
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I agree with K3AN and AD5X that keeping the antennas a good distance away from the house is the first approach to minimizing received (as well as transmitted) interference. I recall my apartment days when my antenna was only about ten feet from my station. I used a few pounds of ferrite beads in my attempts to reduce noise from the computer and other sources.
73,
Chuck NI0C
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RE: Digging Out New Shack RFI
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by W4LGH on December 4, 2006
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One of the major things that will NIX the noise is having you antennas outside away from the house, or anybody's house for that matter if possible. The majority of the noise is picked up at the antenna. Running around your house with a portable ant. was a good approach, but one that really isn't relivant to your ham radio, as the antenna is not is your kitchen.
One thing that I have found in most shacks that cause the most noise is ground loops. Gnd loops are easy to get and sometimes very hard to find and sometimes even harder to correct. Especially in todays world where everyone wants to hook everything together. Computers in your shack can cause interesting amounts of noise. Mainly from the switchmood PS. Also monitors can do the same.
I have a backup antenna in my attic, and the difference of noise levels from this antenna to my antennas out back in the woods is amasing. However living in Florida, with hurricanes, the attic antenna is better than nothing...and it does work.
Best solution.....
Take your portable receiver out to where you will errect your antenna and see what noise you have there. If you can pick several spots, you may be able to dodge any noise you find. Keep your grounds short as possible and to the same point. Do NOT bond your radio ground to your house ground as there is usually several ohms difference in these 2 grounds, which can cause problems. As you know, you can only have a true ground with DC. With AC or RF they should be called commons, and not grounds, as they are only grounded at a given frequency. (ie: if your ground wire is 9ft long, its a 1/4wave of 28mhz)
73 and good luck, you should be ok!
de W4LGH - Alan
http://www.w4lgh.com
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Digging Out New Shack RFI
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by K0RGR on December 4, 2006
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I need to go on a new hunt - my HF bands are getting noisy again.
But something I have found effective is a brute force line filter on the AC mains into the shack - as close as possible to the radio. I put one on several years ago, and it made a huge difference by eliminating noise that is propagated on the power line, rather than through the air. If the power lines in your neighborhood are as grungy as mine, you'll be glad you did. You can take your pick of filters from surplus houses like Dow-Key. It shouldn't cost more than a few bucks.
The noisiest things I've found are the inexpensive amplified speakers for PC's. They seem to have built-in wideband RFI generators!
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Digging Out New Shack RFI
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by WA3YAY on December 4, 2006
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Outstanding! I've learned far more that I could ever hoped for on this topic. Great advice, especially waiting to have my new (old) rig installed and running before I start pulling the wires out of the walls. Thanks guys. 73 - Dave
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Digging Out New Shack RFI
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by AI2IA on December 5, 2006
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Choosing a good location away from sources of RFI and close to earth ground, good grounding of all devices in the shack, using short, flat, and wide ground strips, grounding equipment cases, keeping antenna cables as short as practical, and using top quality ac line filters are all good practices that in total will not cost you an arm and a leg, and will result in a noise free environment. Of all of these, selecting a good location is the most important. As a parting thought, watch your microphones and speakers and their cables. These can cause a lot of mischief, too! Their location and shielding are important.
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RE: Digging Out New Shack RFI
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by NS6Y_ on December 6, 2006
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My particular nemesis is a "windshield wiper" noise that I think has something to do with the boiler in this building, which I"ve learned has had a history of being cantankerous.
Using my little Grundig FR200 as a my sniffer, the signal is REALLY strong in my kitchen along the back wall, especially around and in the sink!
The good news is, the signal is weaker at my ham desk at the other end of this place, and may be negligible once I get some kind of outdoor antenna up.
the Grundig finds my Prius really quite noisy inside, a real ham rig with the antenna outside may have far less trouble.
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Digging Out New Shack RFI
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by GM1SXX on December 6, 2006
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Hi,
I used to suffer RFI... until I disconnected the mains supply ground in the shack and replaced it with the braided inner stripped from some old RG213 connected to the cast-iron drainage system outside using the straightest run I could manage.. through the wall and straight down the outside of the building, terminated in a large tag bonded to the cast-iron drain outside.
Domestic house grounds are a notorious source of RFI. Use a real ground. Thats the best advice I can give.
I use 4 computers in the shack along with several switch-mode power supplies, two large LCD panels and an ADSL router for internet access. My backyard is postage stamp sized so my aerials, a loaded vertical and some wires, are situated close to the house yet the RF background is fairly quiet despite being in the middle of a major town.
I later discovered that my house (semi-detached) was sharing the same short ground spike as my neighbour, hammered into dry soil below my sitting room floor. No wonder I was getting QRM. Real grounds are cheap and effective.
73 Al.
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Digging Out New Shack RFI
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by N6TZ on December 6, 2006
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I too went thru the house and found noisey stuff. So I shut off the main breaker, and guess what, the big noise was still there.....
So what was it??
After thinking long and hard and attacking the problem weeks later, it dawned on me. Shutting off the main breaker does not shut off the BURGLAR AND FIRE ALARM. It has it's own battery and it also has those "antenna" wires running to all windows, doors, etc.
Don't forget this in your quest.
Hal, N6TZ
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Digging Out New Shack RFI
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by KE7AKS on December 20, 2006
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My favorite source of RFI in the shack is the COFFEE BEAN GRINDER! It makes a huge amount of electrical noise on just about all frequencies, but it usually means that my wife is making me a cup of coffee.
I managed to reduce a lot of RFI in my garage/laundry/radio shack by running a copper coated rod into the EARTH,and heavy copper wire grounding system for all the radio case grounds etc. I also found that I dropped a fair amount of noise by doing the same for the house cold water pipes. I noticed that the main electrical panel was already connected to the cold water pipe system. My electrical panel did not have a rod in the earth, but the service is under ground…. I thought that it would have been sufficiently grounded to the earth, but maybe not. Anyway it made a noticeable difference, so I went with it. I can bet some engineers will probably tell me that it can’t work, but it does.
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