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: Broadband noise, S-9 levels above 10 MHz  (Read 3334 times)
AD0AE
Member

Posts: 79




Ignore
« on: November 05, 2012, 06:56:03 PM »

Hi All-

I currently live in an apartment and have recently been experimenting with indoor antenna and thin wire outdoor antennas that I feed between the window screen.  I have been successful in getting the antenna outside, but I noticed something strange.  I am using some simple random wires and off center dipoles using 24 gauge wire, one length of about 33 ft and the other length about 10-12 feet.  I feed both of these ends into a MFJ-949D to match.  I have made a couple of JT-65 contacts.

Anyway, what has been very disturbing is that I thought this would improve my noise problem, but it if anything it is worse.  Everything above 10 MHz I have S-9 levels of noise!  It sounds like "hum".  I took some rudimentary FFTs using the JT-65 software and noticed some regularly spaced lines(separated by about 120 hz - that sounds fishy!) around 14.076 MHz, along with some sort of emission line at 14.767 MHz.  I noticed the S-9 noise levels on 10, 15, 20 and 25 MHz.  40 m had a lot of noise, but I could at least hear something on 40 m, including cw and a few jt-65 stations.  The other bands were totally gone.

While it is an apartment, and there may be many possible sources of noise, are there any things in particular I should try to track down?  More pressing, I have a utility transformer less than 50 feet from my operating station and antenna.  Could that be putting all of this noise out there?  Could it be that the 'bands were dead?'

I could post the FFTs I took using the JT-65 software...?

Any suggestions or help would be really appreciated!

Thank you and 73s,
Steve
AD0AE

Logged
WX7G
Member

Posts: 6192




Ignore
« Reply #1 on: November 07, 2012, 04:56:56 AM »

Steve, it certainly sounds like something in the AC power system is defective (arcing).

I would first shut off the power to your apartment while powering the radio off of a battery. This is to make sure your apartment is not the source of the noise.

From that point sniff around with a portable AM radio to find the source of the noise. If it is the AC power system the utility company will come out and fix it.
Logged
AD0AE
Member

Posts: 79




Ignore
« Reply #2 on: November 07, 2012, 08:11:40 AM »

Thanks for the response WX7G!  I had another ham who recommended that I potentially grab a 3-2 prong adapter and try that to see if I get any improvement.  I have also had the thought about possibly using some software to monitor the S-level on my receiver to see if there is any change in a 24 hour period. We will see, it is hard to say.  Unfortunately I do not have battery capabilities, but I do have an HT I could use to sniff around.

Any further suggestions?

Steve
AD0AE
Logged
WX7G
Member

Posts: 6192




Ignore
« Reply #3 on: November 07, 2012, 09:53:45 AM »

Well, the first step is usually to make sure your house/apartment is RFI clean before hunting outside for noise. A 12 volt battery can be had at Radio Shack for running the radio in receive mode.
Logged
K1TWH
Member

Posts: 103




Ignore
« Reply #4 on: November 07, 2012, 01:44:37 PM »

Steve,   I agree with WX7G, check your own place first.   Unfortunately, there are so many sources of noise out there now, that not having noise at an apartment set up would be like winning the lottery.   Some of the LED bulbs being marketed are dirty beyond belief, switching supply chargers for cell phones, computers, routers and other devices can be very noisy.   On an indoor dipole I use in the summer, I've been chasing an external noise which seems to be 'riding' in on the cable TV line, old unused telco line or the AC mains.  It's S9 white noise till some hurricane comes along and I have no noise for the duration of the neighborhood power outage.  In this case, I've killed power to all the branches, and as WX7G recommends, I power my FT-857D from a 12V 7AH gel-cell.
      If all efforts come up empty, I could suggest using a device like the MFJ-1026 or Timewave-JPS ANC-4 noise canceller.  They can work, but often have limited success with multiple noise sources.
      Best wishes in the noise hunt.    Tom  WB1FPA
Logged
WB2WIK
Member

Posts: 20632




Ignore
« Reply #5 on: November 08, 2012, 05:42:10 PM »

The noise being strongest above 10 MHz likely related to your antenna being more efficient above 10 MHz.  If you had a 130' long dipole in your apartment, I'll bet you'd find the noise is strongest on 80 meters.  Noise peaks where antennas work.

A closed, small loop using a real loop tuner (not what you have, but an actual loop tuner) can be a very effective indoor antenna that will help minimize noise.  I'd try that.

A single-ended unbalanced tuner such as you have won't work at all with a small loop.
Logged
KB5UBI
Member

Posts: 97




Ignore
« Reply #6 on: November 08, 2012, 07:19:36 PM »

At my QTH, most of the noise sources I've managed to track down are worse at 10 mhz and above with any of my antennas including the 75 meter doublet and have been within a mile of my QTH. I do have some 80/75 meter noise but their origins must be further away than most of the 10+ mhz noise I have. When the whole area was without power, the 75/80 meter noise was still there, but I was able to null most of it with antenna phasing.

Some of the bad power line insulators and connectors in the neighborhood were killing 6 and 10 meters with very little effect on 75 meters. Different causes emit different spectrums. The power line Tech can look at the spectral display and have a better idea where to start; transformer, insulator, crimp etc. For what ever it's worth, the Tech I was working with told me the low frequency noise (160 / 80) was the hardest for him to find.   
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!