Help to Locate RF Noise Sources

[a71br]

Build an RFI 'Sniffer Loop' to Help Locate RF Noise Sources

From K5DWJ


Editor's note: The specific source of engine noise can often be determined by using an RF "sniffer loop". The sniffer is not a new idea, in fact these were very commonly used in the 1960's and 70's. It is a classic piece of homebrew equipment that you may find useful in the war against mobil or power line noise. The text below only describes the sniffer as used in mobil systems but the loop is capable to a lesser degree of detecting noisy residential power lines and transformers at relatively close ranges. The usage is similar to that described for mobil use. Note that if you require longer coax lengths you must use a good grade of coax with better than 95% shielding since longer runs of poorly shielded coax tend to receive as much of the noise signal as the loop itself.

What is an RF Sniffer Loop?
This simple device when used with your vehicle's HF rig allows the user to walk around the vehicle and sniff out the origin of local RFI noise. You won't find such a device listed in the ham catalogs and Radio Shack doesn't sell them either. Still, you can probably build your own in fifteen minutes from scraps that you already have lying around the shack. It is basically a close proximity antenna on the end of a long piece of coax. If you are old enough to remember the old "grid dip" meters that we used in the days before antenna analyzers, the close proximity antenna concept will be familiar.

More http://k5dwj.com/ham_rfi_sniffer_loop.htm

http://k5dwj.com/ham%20images/ham_rfi_sniffer/sniffer_loop.jpg=http://k5dwj.com/ham%20images/ham_rfi_sniffer/sniffer_loop_close.jpg=http://k5dwj.com/ham%20images/ham_rfi_sniffer/sniffer_loop.jpg

[AH6OY]

I like the quality and simplicity of the sniffers antenna. I'm wondering how well it works when not very close to the source. I had read a webpage a while back by a man who used a small am radio for sniffing. What he did was remove the telescopic whip antenna and install a little dipole. It was primarily for locating powerline noise and such since transformer will cause static on open bandwidth in the comercial am band local broadcast stations use. Anyway the trick is with a little dipole one side center conductor and the other ground there will be the lobes off the end of the dipole where signal and static will drop. With that reception feature of the dipole you can walk around and figure out one of two directions the source is. Then move in which ever direction and figure out the direction from the reception. I would imagine walking straight towards a powerline making the noise the sense of the source might be hard since the static is rediating from above.
So with all that I think I will try yours first :D
It looks to much more directional.

Thank you very much my friend.

[W8HDU]

I'm dealing with RFI now, and it seems to be turning interesting. One noise source turned out to be our clothes dryer. The sound would be a low growl that would gain in pitch, like the sound of a car engine going through the gears. I noticed that the sound and pitch corresponded to the rotation of the dryer drum.

Now the next question. What to do about it!

[a71br]

Yes the next question. What to do about it! hope to have some answar ..

[W8HDU]

In my situation it's going to be hard to resolve. From the information I've been able to track down, the dryer drum is rotated using a DC motor that appears to be fed a pulsed DC voltage, regulating the speed, and rotation of the drum.

My guess is if I add capacitance to any circuits to filter the DC, it will cause a problem with the speed and rotation control. I might have to operate between laundry sessions.

As for the power line noise, the offending signal was tracked down to a "bell" insulator on the pole. It had developed a small crack and the 12.6 kv on the pole was arcing across the crack. This was the constant buzz that I was hearing on 160-40 meters.

[AH6OY]

I think some how a future of developing land could be pushed towards underground power lines. Then once the specialists (companies) in the regions for design and install of the underground wiring have developed there will probably be an acceptance of the idea to turn above ground wired areas into underground wiring. But eh. There just needs to be the initial acceptance or requirement in some areas to have to have underground wiring. I like the excuse of it makes the skyline look more natural and preserves the environment. This is with my understanding that man will continue trashing the airwaves with power lines till the end of time unless it looks profitable for somebody to have a business burying the power lines.

My short version of this is underground power lines in my neighborhood sure are great.

Best of low noise floors and DX to all of you.