Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: HF Noise  (Read 457 times)
KC6F
Member

Posts: 7


WWW

Ignore
« on: March 09, 2009, 07:24:08 PM »

I've got a question about some "broadband"/white noise I am seeing mainly on HF currently. I have been away from HF for nearly 6 years. I am working in the city next to Boston. However, the noise seems to come and go sporadically. 80 meters has been relatively good tonight and last night. 40 meters has been pretty terrible, ranging from S3 to S5 noise floor. Frequently, I get bursts of noise that fill the entire band for a brief moment.

The question is, how much of this is due to city electrical noise and how much of it is just normal noise on the HF bands? It doesn't sound like its from some digital powerline source or some readily identifiable electrical source. It seems somewhat random and broadband, so perhaps it is not city QRM?
Logged
KB5YLG
Member

Posts: 4


WWW

Ignore
« Reply #1 on: March 09, 2009, 08:01:15 PM »

Could be grounding issues at your station.  An excellent ground system can really benefit your signal-to-noise ratio.

Other than that, take some steps to identify if it is localized, or some kind of long range or ambient atmospheric effect you are detecting, like accumulation of huge numbers of low power BPL transmitters having a cumulative effect on world band hf frequencies, as it certainly *can and does.*

Can you get a direction on it?  Is it on a schedule?  Hook up a car battery to your receiver, then shut off all your house power at the main breaker.  Does the noise go away?

Put your receiver in your car, use a mobile antenna.  Can you drive away from the noise or is it still there everywhere you go?

Is it worse at night?  Worse when it rains?  Better at night?  Better when it rains?

No doubt you can take such steps and figure out what it is, where it is, or at least what it is not and where it is not.

Best wishes!

David KB5YLG.
Logged
KC6F
Member

Posts: 7


WWW

Ignore
« Reply #2 on: March 09, 2009, 08:18:20 PM »

All good questions. My QTH is a 9th floor graduate "dorm" room. I am running a random wire out of the window. I am sure I am picking up a lot of electrical noise, but even people all over 80 meters are complaining about the noise. They are saying the noise floor is S7-S8.

I wish I understood the source of this noise better.
Logged
KC6F
Member

Posts: 7


WWW

Ignore
« Reply #3 on: March 09, 2009, 08:20:15 PM »

I forgot to mention that the ground for my random wire is the metal window frame. This metal window frame is quite substantia, large and elaborate. Upon hooking up the ground, my receive signal levels jump up from nothing to S9. But it might be noisy. I have no idea what it is hooked to. When I ground to the cold water pipe, the noise increases noticeably without much signal increase. So the cold water pipe is noisy.
Logged
N3OX
Member

Posts: 8847


WWW

Ignore
« Reply #4 on: March 09, 2009, 08:58:32 PM »

"It seems somewhat random and broadband, so perhaps it is not city QRM? "

The composite noise of everyone's computer, TV, etc can just be a pretty steady noise floor with random bursts when something particular loud cuts in.

Natural background noise sounds the same as it did six years ago, on average.  If it doesn't sound like natural static-crashy background noise, it's probably manmade.

" But it might be noisy. I have no idea what it is hooked to. When I ground to the cold water pipe, the noise increases noticeably without much signal increase. So the cold water pipe is noisy.
 "

That was my experience operating from an apartment... the balcony railing was noisy :-)  I used magnet wire out to a tree fed against the railing.

I finally got around the problem by shooting another random wire out to another tree and feeding the two as a random doublet with a remote tuner at the feedpoint.

That knocked my manmade noise level down quite a bit, and I was pretty happy with the results for the next couple years...

Basically, fully balanced antennas completely choked off from a building electrical system helped a lot in my situation.

If you're happy with the transmitting performance of what you've got, and just need to hear better, you might try a small receiving loop (with an inductive coupling loop, not a gamma match)

http://www.n3ox.net/projects/rxloop

 or a small version of a terminated receiving antenna like a flag or pennant

http://www.n3ox.net/projects/flag (but smaller)

Even a small dipole with an isolation transformer might help.

It never occurred to me to install receiving antennas (besides the RX loop for 80m, which I later found I didn't need) in my apartment, but I think it could have helped.

That said, make sure your own nose is clean, so to speak.  I didn't really need the RX loop is because the horrible S9 noise I was getting on 80m (which was rather broadband) turned out to be my own computer.  I finally put two and two together when I discovered that the null direction was changing substantially when I moved the loop to different parts of the living room.

I accidentally triangulated it ;-)

73
Dan

Logged

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

Monkey/silicon cyborg, beeping at rocks since 1995.
WA3SKN
Member

Posts: 5559




Ignore
« Reply #5 on: March 10, 2009, 08:58:14 AM »

LOTS of possibilities here!
Do you have the noise with a dummy load?  This will eliminate internal radio noises and noise incoming via the power supply.
Most probably the noise will be incoming via the antenna.  (There is a slight possibility of it incoming via the ground!)
Now comes the noise source(s).  Get a long run (50-100 ft) of coax and make a small loop on the end.  This will be a "sense" loop for trying to locate the noise.  You won't be able to use a battery power source and kill the breakers in a dorm environment.
Most probably your noise(s) will be from the computers and LAN in the dorm area.  These square waves have lots of harmonics and were not designed around radio use in the area. If it just the wires in YOUR area, you might be able to shield them enough with aluminum foil or metal tape.
With a shared area, this one is going to be a challenge... Good Luck!

-Mike.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!