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Author Topic: Strange 160 Meter Buzzing  (Read 232 times)
N1ZHE
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Posts: 68




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« on: January 20, 2006, 08:19:10 AM »

I'm running an Icom IC-706MkIIG into an LDG AT-11MP Autotuner into a short run of coax to a LDG 4:1 balun, feeding a little over 100 feet of 450 ohm ladder line, and that (finally!) feeds a Spi-ro AS-2 shortened
all-band dipole. This dipole has loading coils on each leg. This antenna is advertised as being able to work 160 meters with a good tuner.

This setup works beautifully on all bands EXCEPT 160 meters. I can tune to about a 1.8 to 1 SWR for transmitting.

However, my receive has a strange buzzing that sometimes is "just there" and sometimes it isn't. This noise usually tends to only be apparent when I am receiving a signal from another station.

The noise rises in intensity with the received voice peaks. Right now I'm on 1.988 and the nearest next QSO is on 1.940.

My antenna is only about 25-30 feet up, about level with the top of my roof on my two story wood frame house. Getting up higher is not much of an option at this time.

One leg of my antenna is about 15-20 feet from some neighborhood power lines.

Due to my really small lot, I can't arrange the antenna any differently.

Sometimes this noise completely goes away and the receive is beautiful.

Because I'm on the second floor, I have not grounded my equipment.

The buzzing does not sound electrical and I have all but eliminated any sources in my house.

Do you have any suggestions how I can eliminate this buzzing?

David, N1ZHE
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WB2WIK
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Posts: 20540




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« Reply #1 on: January 20, 2006, 09:42:25 AM »

Welcome to 160 meters, Land of the Noise.

Noise propagates really far on 160.  One wavelength is 540 feet.  Anything within 540 feet of you generating noise is likely to cause real problems on 160 meters.  I can hear stuff like electric fences two miles away.

Based on the symptoms you describe, although I have absolutely no idea what's causing your noise, I do have some suggestions about how to operate your rig:

1.  Sounds like your noise blanker is ON, so received signals are being noise modulated.  That would explain why the noise is most noticeable when you tune across stations.  It's also very possible or likely that the noise blanker is affected by other signals in its first IF passband, which is wide as a barn door, so any strong signal anywhere on the band might "modulate" the noise when you're listening to another station elsewhere.  Very common problem with cheap noise blankers.

2.  To find out if this is the case, turn the NB "OFF."  Then, you should hear the noise everywhere, and it won't modulate with signals.

3.  If that's the case, turn the NB back on.  If your NB has multiple options (1-2-3  or narrow-medium-wide or whatever), experiment with those.

4.  Make sure your PREAMP is OFF!!!  Nobody needs a preamp on 160m when they're using the same antenna to transmit and receive.  Indeed, you might try using some ATTenuation instead.  A lot of times, noise problems can be partly resolved by adding attenuation (10 dB- 20 dB, whatever) in front of your receiver because that might knock the noise down more than signals.  If you reduce noise by 11 dB and signals by 10 dB, you've just gained a 1 dB signal-to-noise advantage, which you can hear.

5.  A lot of HF transceivers aren't the greatest on 160.  I know among the few that I presently have, it's obvious which ones work best on this band.  This band is a huge challenge, fightning noise sources and some receivers deal with it better than others.

WB2WIK/6
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KB9CRY
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« Reply #2 on: January 20, 2006, 01:06:37 PM »

Welcome to the world of Top Band and welcome to the world of marketing.  Yes, I'm sure that that little antenna will work something on 160, but.....Why do you think all the big guns have larger antennas and have all these long beverages and flags and stuff?  Because they need it.

Also, please not to be meant personal, you are using a little mobile radio that doesn't even have the room inside of it for all the stuff needed for a good Low Band receiver.

I'd experiment with the suggestions made so far, but eventually you'll need to change that antenna and get serious with it and the same can be said about the radio.

That's the beauty of Amateur Radio, there's always room for more improvement.  Phil
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WB2WIK
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Posts: 20540




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« Reply #3 on: January 20, 2006, 01:49:52 PM »

Afterthought comment:

I'll bet your lot in Maine isn't any smaller than my lot in Los Angeles.  And I have a 160m dipole, up higher.  It fits the lot because it's an inverted vee, and its center (feedpoint) is up about 60' above ground on my tower, so the "ends" of the antenna aren't that far apart -- about 170 feet.  It stretches the diagonal of my lot and just makes it onto the property, which is less than a quarter acre.

The tower doesn't occupy any "property" at all, other than a 3-1/2' square concrete pad.

A shortened dipole at 30' for 160m is a really "local" antenna, so the noise problem you describe, while annoying, probably isn't preventing any contacts...

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N6AJR
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Posts: 9879




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« Reply #4 on: January 20, 2006, 02:59:27 PM »

look at the gap Voyager, I just work alabama from northern Ca, last nite and a mobile in Montana, check into the century club early and late nets on 160 (1.892) in the evenings, (pacific tim) do a google on 3905 century club.. lots of info.  but you need an antenna and a good rig to be effective on 160 ( orion/ alpha 87a/gap voyager just is an "ok" set up) so top band is fun but needs specific stuf..
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W8JI
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« Reply #5 on: January 20, 2006, 04:20:50 PM »

Stay away from a Gap antenna. My Mobile antenna 13 ft tall will blow away a Gap vertical on 160!

What you might try to do is put in  aradials system and load your antenna as a T against that system.

As to the noise, do you have the blanker on? Is it a high pitch sharp buzz or more like a hum?

73 Tom
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KC8VWM
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Posts: 3124




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« Reply #6 on: January 20, 2006, 06:09:38 PM »


Yup, Isolating and correcting the interference at the source is the answer. Relying on your noise blanker to fix these problems for you is not always the answer.

I would try to specificallly identify if the noise is coming from that powerline one leg of your antenna is 15-20 feet away from.

Walking around the yard with a portable AM radio in hand might reveal the source.

Grounding will help your situation even if that ground is some sort of makeshift compromise.

Keep us updated on your progress.

73
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