Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Interference source found




 
The AM Forum
March 05, 2021, 07:29:53 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Interference source found  (Read 4369 times)
0 Members and 1 Guest are viewing this topic.
k4kyv
Contributing Member
Don
Member

Offline Offline

Posts: 10062



« on: February 12, 2005, 06:04:37 PM »

To-day was warm and pleasant outside, so I did some serious rf sniffing, and located the source of the mysterious tone-modulated carrier every 30 kc across the spectrum from 3 to 30 mc!

It pays to check your own house first.  It turned out to be my no-name cable modem.  While nothing else affects it, unplugging the modem from the ac mains completely kills the signal.

So far, that's the only way I can kill the noise, though.  I tried an ac line filter on the power cord, and tried clamp-on ferrite chokes on both the power cord and coax cable, with no noticeable effect on the interference.  I have the model number and serial # of the unit, but no manufacturer's name on the unit itself or the box it came in.  I sent a letter to the  local cable company, and will wait to see if they offer any assistance.

One problem is that my computer room is located upstairs in what used to be my hamshack, so I suspect that every electrical conductor in the vicinity of the computer acts as an antenna. The UPS unit generates its share of digital rubbish as well.  

There may be no solution short of  building a completely shielded computer room, on the ground floor, lined with copper screen.  (Hey Marty, can I call on you for a contribution?)
Logged

Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

- - -
This message was typed using the DVORAK keyboard layout.
http://www.mwbrooks.com/dvorak
WA1GFZ
Member

Offline Offline

Posts: 11152



« Reply #1 on: February 12, 2005, 07:57:09 PM »

Don,
Why not put it in a shielded box with beads on the leads. Feed through filters on the power leads. Sounds like switching power supply noise.
Logged
W1RKW
Contributing
Member
*
Online Online

Posts: 4255



« Reply #2 on: February 13, 2005, 08:12:38 AM »

Don,
Is there an FCC ID tag on the modem?  If so, you may be able to find the manufacturer that way via the FCC database which is on the FCC website.
Logged

Bob
W1RKW
Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
w3jn
Johnny Novice
Administrator
Member

Offline Offline

Posts: 4604



« Reply #3 on: February 13, 2005, 08:33:07 AM »

Don, the signal could be radiating from the data lines.  Try a bunch of chokes on everything.   In my experience one small choke doesn't do it.  You may want to try a brute force L/C line filter - some of those "line strip" line filters are worthless.

73 John
Logged

FCC:  "The record is devoid of a demonstrated nexus between Morse code proficiency and on-the-air conduct."
K6JEK
Contributing
Member
*
Offline Offline

Posts: 1165


RF in the shack


« Reply #4 on: February 14, 2005, 06:10:58 PM »

My name brand (Motorola) cable modem broadcasts like crazy on 3880 and 3880/2. I wrapped the power cord  through a RS snap-on, as many turns as I could get then did it two more times with two more chokes.  This helped a lot but not enough.

I built a special Ethernet cable sans insulation so I could get a lot of turns through a mix 77 torroid.  This helped not a whit.  It's very pretty, though, with all those colorful twisted pairs wound on the donut.  

I'm thinking of shielding the box with copper screen.  I'm also thinking of modifiying it with a sledge hammer.

Moto gave me a legalistic repsonse when I finally got through to them.  I should have saved it for everyone's amusment.


Jon
Logged
Steve - WB3HUZ
Guest
« Reply #5 on: February 14, 2005, 07:47:38 PM »

Aluminum screen will work just as well.
Logged
Vinnie/N2TAI
Guest
« Reply #6 on: February 15, 2005, 08:50:07 PM »

Had the same problem with two Motorola Cable Modems 20 over 9 noise all across 80 meters. Shielding with aluminum screen and grounding the screen to the cable shield helped a lot also had clamp on ferrites on the power cord and 10 base T cable to computer droped noise to S5 over 9. Fortunately the modems are provided by Time warner cable and after making a lot of noise they changed it to a Moto Dx-100 no more interference then that one failed so now I have A moto SB4100 and no noise with this one either.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.052 seconds with 18 queries.