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Author Topic: Broadband RFI on Lower HF Freq  (Read 9254 times)
W2MV
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Posts: 244




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« on: December 15, 2010, 06:04:43 AM »

From approx 6 MHz up to at least 10 MHz, can't hear it on 14 MHz. I snooped around with a portable receiver tuned to 7 MHz and a whip antenna. RFI pickup seems to peak near any a/c power line, but especially near any appliance with a large metallic surface such as window a/c's and the fridge. The RFI is really strong near my landline phones and phone wires....hmmm...

I'm not sure if what's bothering me on my  IC756 PRO3 is the same thing I'm picking up with the portable receiver, but in any case I did the circuit breaker test. One by one I turned breakers off and back on while listening to my Icom. Fortunately, the breaker panel is in the shack.  None had an effect on the 7 MHz RFI, so I'm assuming that the source is external, possibly even coming in via a copper telephone line.

This RFI is relatively low-level, but strong enough to interfere with weak DX, so driving around and trying to locate it will be difficult if not impossible. Any suggestions?

Thanks,
Alan, W2MV
« Last Edit: December 15, 2010, 01:45:39 PM by Alan Burg » Logged
K8AC
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Posts: 1912




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« Reply #1 on: December 17, 2010, 06:28:17 AM »

In our area, the phone line box on the side of the house uses a plug (RJ11 or RJ45) to connect the line to the house wiring.  So, if I suspected a signal were coming in on the phone line, I could just unplug it outside for a test.  You might want to check that - you'll likely have to remove a screw or two in order to open the door on the box.
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AB8AL
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Posts: 19




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« Reply #2 on: December 29, 2010, 05:37:12 AM »

For the circuit breaker test you should turn the main off and if the noise is gone start turning them on 1 at a time.  At any point did you have all the breakers off and running the radio on battery power  If not start there.
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NO2A
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Posts: 1400




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« Reply #3 on: December 29, 2010, 07:10:19 PM »

Just a guess,you might try using an a.m. broadcast band radio as noise r.f.i. will be more easier to hear than a portable on 7 mhz.
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WD8KDG
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Posts: 45




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« Reply #4 on: December 30, 2010, 04:52:12 AM »

With your portable receiver, have you walked around the neighborhood? As the RFI gets louder/stronger shorten the whip antenna. This should get you real close to the source of the RFI. Also consider the fact if the source is in another nearby home, the source could couple to the support cable which holds cable/phone utilities between poles.

I have this problem in my area, the support cable acts like a long wire antenna and the RFI seems to be almost everywhere along the street, but after several trips around the block, the source was located.

So far, no luck with the neighbor and the device generating the RFI................been swapping e-mails/complaints with the FCC for over 6 months.

Good Luck in your search, Craig
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WB4BYQ
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Posts: 185




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« Reply #5 on: December 30, 2010, 05:56:06 AM »

To WD8KDG,

The ARRL has a memorandium of understanding with the FCC, to handle complaints thru the ARRL to the FCC.  Contact the ARRL RFI department Mike Gruber, W1MG at phone
number 860-594-0392 or at w1mg@arrl.org.  the arrl will write a letter very much like
the what the FCC would send if you will file a complaint thru the ARRL.  A copy is sent
to the FCC also.  I have used the ARRL two times to work with neighbors, and it does
work.

richard
wb4byq
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WD8KDG
Member

Posts: 45




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« Reply #6 on: December 30, 2010, 09:59:39 AM »

To WD8KDG,

The ARRL has a memorandium of understanding with the FCC, to handle complaints thru the ARRL to the FCC.  Contact the ARRL RFI department Mike Gruber, W1MG at phone
number 860-594-0392 or at w1mg@arrl.org.  the arrl will write a letter very much like
the what the FCC would send if you will file a complaint thru the ARRL.  A copy is sent
to the FCC also.  I have used the ARRL two times to work with neighbors, and it does
work.

richard
wb4byq



Neighbors have ignored the FCC and my attempts to resolve the issue. At this point Part 15 appears to be just smoke and mirrors. What is to fear from the ARRL?
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WB4BYQ
Member

Posts: 185




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« Reply #7 on: December 30, 2010, 03:40:07 PM »

Has the FCC sent a letter to the neighbor? 

richard
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W2MV
Member

Posts: 244




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« Reply #8 on: January 03, 2011, 05:28:26 AM »

To AB8AL:

Yes, I did shut off the main breaker during my test, but unfortunately the 40M broadband noise was still present.

Thanks
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K1DA
Member

Posts: 744




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« Reply #9 on: January 17, 2011, 08:38:01 AM »

  I have heard suggestions that the new UHF TV transmitters are producing white noise on 160 through 40.  I have something here which produces a strong signal.  I have performed  the suggested tests but have been unable to locate the source.  I'll keep digging. 
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W2MV
Member

Posts: 244




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« Reply #10 on: January 17, 2011, 08:43:15 AM »

By UHF TV transmitters, you mean broadcast TV stations, right?
I don't have any close to me.
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KH6AQ
Member

Posts: 8001




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« Reply #11 on: January 17, 2011, 09:12:21 AM »

I recommend the MJF-1025 noise cancelling unit. The AUXILARY, or sense antenna, needs to be decent and have a gain of not more than 10 dB below the MAIN antenna.
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W2MV
Member

Posts: 244




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« Reply #12 on: January 17, 2011, 09:51:13 AM »

I use an ANC-4. It helps...sometimes, but the characteristics of the sense antenna can make a big difference and you need to experiment.

It does not seem to help with this low-level broadband noise very much, no matter what I do.

Does anyone have experience with the ANC-4 vs the MFJ unit?
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KH6AQ
Member

Posts: 8001




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« Reply #13 on: January 17, 2011, 11:25:36 AM »

Link to an article By W8JI on the MFJ-1025/1026: http://www.w8ji.com/mfj-1025_1026.htm

Quoting the article:
"Even with MFJ's well-known QC issues and affinity for building things cheap (not good) I still recommend the MFJ-1025 over all other mainstream units. It has the potential to be better than anything else with only minor changes, and is certainly betetr [sic] than all other mainstream units like the ANC-4 or QRN Squasher just as it is shipped."
« Last Edit: January 17, 2011, 11:27:14 AM by WX7G » Logged
W2MV
Member

Posts: 244




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« Reply #14 on: January 26, 2011, 10:01:50 AM »

Update!:

The external 40M broadband RFI I have seems to vary with the amount of snow cover in the area.
I noticed that after a snowfall, the RFI level on my S meter drops from S 6.5 to S 3.5. Now I'm thinking that perhaps the coax to my 40M dipole, being buried in snow on my roof, is experiencing choking/common-mode attenuation by the snow it's embedded in, compared to when it's in the clear...just an hypothesis!
That might imply that my RFI is being picked up on the coax, from coupling with the a/c wiring in the house....again, just an idea. The dipole has no balun; it was installed the days before I experienced this RFI and worried about this stuff.

Alan, W2MV
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