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Author Topic: Does a quality HF RFI "sniffer" exist?  (Read 36864 times)
KB3BTO
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Posts: 41




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« on: November 03, 2010, 01:44:53 PM »

  I've been haunted by RFI that ranges from 16-29MHz for the past several years during the winter months and have been unable to pinpoint the exact source. As if this weren't bad enough, it's intermittent in nature. Every time the utility company sends their rep with his precision gear, the RFI is no where to be found at that time. (We've toyed with the idea of him leaving his truck parked in my driveway, but, sadly, that wasn't practical.)
  Anyway, is there a home brew design, kit, or "store bought" model that doesn't cost a fortune, works reasonably well, and is available for construction or purchase? I've read a lot of articles that relate to VHF type locating, such as the VK3YNG MK4, but that doesn't help a 10 meter fan like me.
   Any serious assistance is greatly appreciated.

   73
   Charlie
   KB3BTO
 
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KH6AQ
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Posts: 7891




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« Reply #1 on: November 03, 2010, 02:31:19 PM »

A cheap battery operated short wave radio will do the job.

Radio Shack stores sell the Grundig Mini 300 AM/FM/SW Pocket Radio for $19.97. I have one of these radios and it's adequate for finding RF sources.
« Last Edit: November 03, 2010, 02:34:22 PM by DAVE CUTHBERT » Logged
KB3BTO
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Posts: 41




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« Reply #2 on: November 03, 2010, 04:10:01 PM »

  I've already tried a portable SW radio. Specifically, a Gundig YB-400 with its telescoping antenna and then an external, long wire antenna. It's not exact enough, apparently. I can determine that there's RFI but I can't, as of yet, find the exact source.
  I was hoping for something with a hand-held, Yagi antenna configuration to be more precise in locating the source, something that will let me tell the utility rep, "It's that pole, pole number..."
  Maybe I'm looking for something that doesn't exist or isn't necessary for most situations? Maybe I should try a different portable SW radio?
  The RFI gives me an S-7 reading on my TS-940 when I'm anywhere on the 10 meter band. This is most frustrating.
  Thanks for your response. It is appreciated, honestly.

  Charlie
  KB3BTO
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N3OX
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« Reply #3 on: November 03, 2010, 09:32:41 PM »

I went through this recently and ended up purchasing a Yaesu VR-500 portable receiver and pairing it with homemade antennas.  The receiver is capable of AM and SSB reception on HF, VHF and UHF.  The VR-500 wasn't super cheap... something like $250.   But it's very versatile because it covers a large frequency range and I can use different antennas for different problems.  It seems to be discontinued but there are others like it.   For what I was doing, hunting mostly power line noise, something that does AM reception on VHF and UHF is really great.  Having HF in the same package is nice.

It seems to be discontinued. 

I have three noise hunting antennas right now.  I have a 18 inch diameter magnetic loop that will tune from about 10-40MHz.  I have a 2m Moxon Rectangle and a 5 element 438MHz yagi.  Usually I'm hunting power line noise with a general heading known, and I only need the UHF yagi.  By far it is the most precise pinpointer.  The 2m Moxon is broader but works from a further distance, typically. 

The magnetic loop can be used for some direction finding provided that the noise is a concentrated source a medium distance away.     You could try one on your Grundig, I suppose.

The magnetic loop doesn't work to actually locate noise coming from or conducted by power lines.  The thing about power line noise is that they get excited with HF along the whole length and then you get interference patterns. 

I need the UHF yagi for actually showing me which pole is the problem and even possibly which part of the pole.  I still haul the magloop around if I'm hunting an intermittent pole noise, especially if it is one of many... that way I know whether or not the noise that's causing me trouble on HF is actually associated with the UHF reading I'm getting off of some pole.

It's good to have a diverse set of possibilities, and a broadband AM/SSB capable receiver that included VHF and UHF was the ticket for me.



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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KB3BTO
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Posts: 41




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« Reply #4 on: November 04, 2010, 04:57:02 AM »

   Thanks, Dan. It would seem that I must pursue something in the UHF range to pinpoint the problem. I had hoped that there was a similar design for HF sniffing but that doesn't seem to be the reality. In fact, the utility rep has a dandy piece of gear that displays the frequency peaks and uses a Yagi, hand-held, antenna that sniffs in the UHF range but it's a professional piece of gear that costs a few thousand dollars.
   I've searched the ARRL Handbooks and RFI book and the internet for a more defined HF sniffer but I will now have to change gears and focus on UHF equipment.
   I am convinced that it's power line in origination. The wave forms displayed on my Kenwood SM-220 station monitor and sound bites of AC noise from the internet are consistent with power line interference. Now all that I have to do is to prove it.
   I'll snoop around for that radio that you mentioned, Dan.
   Another ham adventure is about to begin.
   Thanks to all.

    73
    Charlie
    KB3BTO
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AA4HA
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Posts: 2630




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« Reply #5 on: November 04, 2010, 07:37:40 AM »

A Yagi in HF would be quite large and probably not something you could even carry. What works just fine is a ferrite rod antenna scavenged from an old AM radio.

As has been mentioned, looking for the exact origins of HF interference is complicated by the fact that when you are that close in, being directional does not help you much.

There is a class of receivers that were used for LW/MW/SW DF work. Usually you would find them on boats and ships and some would have a rotatable top dome that could be spun around to give an approximate azimuth to a shore station. You can imagine that being in a tuna boat a few hundred miles away from the coast it would be helpful to triangulate your position from shore based AM radio stations. These types of receivers still come up on eBay from time to time. They are pretty much useless for finding a problem within your own house or in finding what insulator is sparking on what utility pole.

Leaky insulators generate a significant amount of broadband interference. I spend a great deal of time hanging out with electric utility types and one of them described his way of finding a leaky insulator;

He would tune to a quiet spot in at the bottom of the AM band of his truck radio and drive around town. When the signal got louder he would tune to the upper part of the AM band and drive around in a smaller area. This usually got him to within a block or two. Then he would use the two way voice radio in the truck with the squelch opened up and listen for an increase in the static level. Their voice system operated in the 30-50 mHz band (between 10 and 6 meters). This would get him to within 2-3 utility poles. If he could not see the leaky insulator by then he would tune up his FM radio to a quiet spot in the 88-108 mHz band and usually he could hear an increase in noise when he was right under the pole that had the bad insulator.

It all sounded like a load of hooey but it does work and does have a basis in sound engineering principles. It works for leaky HV but would not do you much good to find out if it is the plasma TV or the toaster that is causing the noise (unless your wife will allow you to drive your pickup truck into the living room. HI HI).

Tisha Hayes
AA4HA
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
AA4PB
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« Reply #6 on: November 04, 2010, 08:05:37 AM »

The MFJ-856 may be what you want.
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Bob  AA4PB
Garrisonville, VA
NO9E
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Posts: 883




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« Reply #7 on: November 04, 2010, 10:20:02 AM »

See the professional equipment on http://www.radarengineers.com/rfitvi.htm.

My power company has it. It makes identifying sparking poles a breeze in comparizon to AM radios, 3-el MFJ sniffers etc.  It also makes it easy to distinguish between different types of RFI. Guys from my local power company let me use it around the house.

Ignacy, NO9E
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AA4PB
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Posts: 15046




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« Reply #8 on: November 04, 2010, 10:34:15 AM »

I'll bet it costs way more than most of our stations.
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Bob  AA4PB
Garrisonville, VA
KB3BTO
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Posts: 41




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« Reply #9 on: November 04, 2010, 03:10:31 PM »

  Okay, and thanks to all.
  The utility rep here uses the "radarengineers" equipment, too. It's dandy but, as I mentioned, each and every time that he gets here the RFI stops. I'm convinced that it's either loose hardware or a cracked insulator that's producing a "spark-gap" RFI because it's only present during cold weather and ceases immediately when it's raining or extremely foggy. Of course, it could be transformer but the utility rep did a visual check from the ground on nearby poles and didn't see anything suspicious.
  As of right now, here's my game plan: I'm going to try a different radio to locate the exact source of the RFI. If that fails, I'm going to bite the bullet and purchase the MFJ-856. I would prefer not to make that purchase but I've been chasing this RFI ghost for 3 winters now and...enough is enough. One day soon 10 meters will open to a reasonably decent band and I want to be ready and waiting.
  Thanks for all of the constructive input, folks, and "happy hamming to you."

  73
  Charlie
  KB3BTO
   
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AF4O
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« Reply #10 on: November 04, 2010, 04:41:21 PM »

I dealt with intense rfi for years and its a looooong story. Anyway to answer your question best i can; First of all, if you have multiple sources, it can get confusing. Kill the loudest and move on.

I first use my FT-817 on AM mode on batteries with the strap around my neck and a 2 meter lightweight 4 element quad. I bought the quad on that big auction site years ago. IF the noise is intense enough to go up to 2 meters (most all of mine have been especially as you get close which helps to isolate) then use this to triangulate to find the pole or area of the noise. Next i use an ultrasonic detector with a small parabolic dish. There was an article in QST years ago of how to build this device. And in my opinion, with practice, its fantastic. I take the pole/area in question and carefully scan the hardware to usually narrow it down to < 3 pieces of hardware. The dish is a near pinpoint device. Maybe <12" detection area at 20'. Then i take a digital picture and email the power company.

Other clues, such as weather affects it, time of day, etc sometimes will help. Also i have towers/beam antennas for 2m and 440 that i can often find the general direction.

I too got to having trouble getting the rfi experts to just show up and of course the noise would be absent. Taking off work to meet them, etc got to be a pain. There had to be a better way. My neighborhood is 60's and old utility poles all about. The first round they found about 12 sources. Since i often locate with the methods above.

Also, I have an ANC-4 which, if used properly can work wonders. Yes its a pain to tune, you have to have good sense antennas, and some noise it does not help. But it can be a game changer when it comes to the occasional pop up noise.

And finally ive taken up field operating QRP gear in the parks. Nothing like the clear noiseless background of hf like being in a park :-)



73
Chuck
AF4O

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WB6BYU
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Posts: 18463




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« Reply #11 on: November 10, 2010, 10:14:20 PM »

I think Dan already covered the basics.  On HF about the best you can do is a loop, which works well
enough when you are searching for a point source, but it is impossible to track a null with the signal
radiating from hundreds of feet of wire.  In that case the best you can do using a portable HF receiver
is probably walk (or drive) along the wires to see where the signal is strongest.  Do this on the highest
HF frequency where you can hear the noise, as it dissipates faster with distance.

Then, as you get closer, move up into VHF where you can get a more accurate bearing with a yagi or
other beam antenna  - it is easier to find a peak instead of a null.  I happen to have a number of good
VHF DF receivers (including the VK3YNG) but the VR-500 with a 3-element yagi is quite sufficient for
at least confirming the right pole.  (It gets more confusing when the source is leaks in a cable TV system
and there are at least 18 of them on every block.)  Again, any VHF AM receiver can be pressed into
service - a ham rig with aircraft band receive should work with an appropriate antenna.  (If you know
someone in CAP or Search and Rescue, see if they have access to an ELT DF receiver, though you may
want to build an extra beam antenna for it.)

VHF/UHF antennas are simple to build - I use the WA5VJD "Cheap Yagi" designs described here:

http://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf

I've modified them for other bands from 121.5 MHz to 732 MHz and they are very easy and inexpensive
to build.

I can provide details of a tuned HF loop if you want to try that - mine tuned something like 6 to 20 MHz,
so not quite  the 4 : 1 range that Dan achieved, but again it is just a wood framework with a few turns of
wire on it and a way to couple it to a receiver.  Oh, and a tuning capacitor.  You can connect it to your
home rig and tell by the background noise when it is tuned to frequency.

Good luck!
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K7AAT
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Posts: 38




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« Reply #12 on: November 14, 2010, 10:56:17 AM »


  There is a rather inexpensive ultra-sound device with small parabolic dish available for tracking down such power pole issues you describe as cracked insulator and hardware arcing.  They advertise occasionally either in QST or CW magazine.   

  Or you could build your own:  http://www.arrl.org/power-line

  or     http://www.midnightscience.com/ultrasonics.html

  or     http://www.exergia.info/books/analog_nonlinear/hanson.pdf

  Ed   K7AAT

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ZENKI
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Posts: 1636




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« Reply #13 on: December 04, 2010, 02:27:36 AM »

Just use a Icom R20 or Degen shortwave receiver with a small loop no more than 0.5 meters. Try and find a old Empire loop on epay.
The nulls on this loop make easy work of  finding noise in your house. This small 0.5 meter loop with a 20 db advanced receiver research preamp attached to the car roof with a magnetic mount makes driving around the neighborhood finding noise very easy. You can make one
just follow the loop balance rules on W8JI's web page.

The MFJ power line yagi when used with a IPOD AAA battery  amplifier makes finding noise inside the house. Yes, the yagi is big but it hears everything that causes noise and if you dont live in a dog box you can point the yagi in the house.

Make small sniffer probes that attaches  to your HF radio. I like using my K2.
http://www.emcesd.com/tt2008/tt050408.htm This link shows you how to make these sniffer probes, I have several different sizes. A small
enamel wire quad of about 2 inches per side attached to my K2 find any noise right down to the part on the PCB!

The audio amp with telephone pickup in the ARRL handbook is also a must have for finding  and showing your neighbours what the noise sounds like. Its also a good tool for your own house.

Good luck, once you start you become obsessed about hunting down every weird noise in your receiver.

Whatever you do  never move next door to a railway line, even in the countryside. The Westinghouse modern signal systems use a form of BPL that jams the HF bands. Even big companies like these ignore EMC laws.





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K4FH
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« Reply #14 on: December 27, 2010, 09:30:29 AM »

I think one problem might be Christmas lights.  I get a lot of "bacon frying" this time of year but it seems to go away after people take down the decorations.
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