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Author Topic: QRM on 40M at night  (Read 1996 times)
WK5H
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Posts: 111




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« on: March 01, 2011, 08:46:58 PM »

Seems like the last year or so (worse in the last few months), there has been an undulating whooshing white noise that just blankets the 40M band from around 7.180 to 7.200 at night.  It hangs around an S7-S9, and makes any work on the general band at night useless.

Anyone else heard it or know what this is?
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K2OWK
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Posts: 1061




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« Reply #1 on: March 01, 2011, 08:56:02 PM »

There is a lot of noise on 40 meters in my location all the time. At night the band is not very active, but there are many foreign AM stations active at this time. Most frequencies are useless at 7.200 and above. I do not know if this is the problem you are having or not, but maybe this will help.

73s
Barry K2OWK
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N3OX
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« Reply #2 on: March 02, 2011, 06:32:55 AM »

You mean this noise?

http://n3ox.net/files/40m_noise_LSB_022211.mp3

Sorry if the audio level in that file is too quiet.

At about 40 seconds in, I tune off of the noise ... at about 1 minute I tune back on to it.

If that's the noise, I've been wondering that too.  In googling around I've found some suggestion that Ethiopia has been jamming Eritrean broadcasters in the past couple of years, and the frequencies used by those jammers fit where I've heard this noise.

Not sure if that's the source, but whatever I'm hearing is loud and ugly and obliterates big chunks of the band, including the upper broadcaster-free part of the general band you're talking about.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WK5H
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Posts: 111




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« Reply #3 on: March 02, 2011, 06:05:49 PM »


THAT'S the noise.  The only good thing I can say about it, is that it's been a great incentive for studying for my extra class ticket...
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N4JTE
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Posts: 1155




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« Reply #4 on: March 02, 2011, 06:35:44 PM »

Doubt Eithiopa could ever generate that kind of signal, however the HAARP military weather changing vast antenna array is the more likely suspect.
Bob
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N3OX
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« Reply #5 on: March 02, 2011, 06:46:33 PM »

THAT'S the noise.  The only good thing I can say about it, is that it's been a great incentive for studying for my extra class ticket...

Grin

Always good to have incentive.  It unfortunately takes out big chunks of the Extra band too, but there's still some open real estate.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KG4YMC
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Posts: 297




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« Reply #6 on: March 03, 2011, 08:23:18 AM »

I have heard that noise also,sometimes 40 sounds like an ocean roar , no I am not holding a seashell to my ear, but it sounds like the old shorwave broadcaster jamming type stuff, also at night the broadcaster give the band a fit , but late at night if there is openings , dx it is usually from 175 to l90 . I am working night shift so haven't been on lately . kg4ymc   florida ham . 
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K4KYV
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Posts: 41




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« Reply #7 on: March 03, 2011, 12:12:24 PM »

The hash is coming from Ethiopia.  They are jamming The Voice of the Broad Masses of Eritrea, which broadcasts in the supposedly broadcast-free portion of 40m, starting at 0300 GMT. Their strongest and most consistently-used frequency is 7175, but additional frequencies include 7165, 7130, 7120, 7185, 7195 and probably others. They usually simulcast on 2 or 3 of the above frequencies, and sometimes hop around to dodge the Ethiopian jamming.  I have heard them play a cat-and-mouse  game by hopping amongst the above frequencies, only to have the jammers follow them within minutes of QSYing. At times I have heard another Ethiopian sounding BC station zero beat the carrier, and then the hash come on top of that, so you have two broadcast stations zero beat with each other plus the noise. The Eritrea  station also  transmits a different program on 7205, but I have never heard the jamming stations bother them on that frequency, although the jamming has been heard centred on 7220.

The broadcast from Eritrea can be positively identified by listening just a few minutes before sign-on at 0300Z to the interval signal, which is the sound of strumming on a guitar, broken up with announcements in the local language.  The sound of the interval signal can be verified at http://www.intervalsignals.net/ (the site is down right now, but they promise to be back up in a few days). Find Eritrea on the list, and click on the link to hear an audio clip of the interval signal.

The jamming usually starts up at about 0400 GMT and continues for 1 1/2 to 2 hours. I suspect it  disappears when propagation to  that part of the world goes out as they move into daylight (Ethiopia is 3 hours ahead of GMT, so at 0600 - midnight CST - it is 9 AM in Ethiopia.)

I read a report somewhere recently that China had furnished 4 jamming transmitters to Ethiopia.  Although the targeted broadcaster occupies only about 10 kHz of spectrum, each white-noise jamming signal is usually more than 20 kHz wide. When all 4 jammers are running simultaneously, they pretty well render the entire supposedly broadcast-free segment of 40m useless in N America.

I first noticed this noise right after the broadcast stations first vacated 7.1-7.2, but it had probably already been there for a long time, masked by stronger broadcast signals coming in from Europe.http://www.iaru-r1.org/index.php?option=com_content&view=article&id=308:radio-ethiopia-which-is-jamming-voice-of-broad-masses-from-eritrea&catid=39:iarums&Itemid=87
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