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: Prev 1 [2]   Go Down
  Print  
Author Topic: Cable Modem RFI  (Read 11362 times)
K1CJS
Member

Posts: 6055




Ignore
« Reply #15 on: April 24, 2013, 03:27:33 PM »

Keep your eyes open at yard sales.  Sometimes you see older 12 volt 5-7 amp power supplies that were used for CBs in years past.  They're about the best because they're filtered and have plenty of capacity to run the modem.
Logged
KD8TZC
Member

Posts: 67




Ignore
« Reply #16 on: April 25, 2013, 10:17:33 AM »

And how can you tell if one is filtered?
Logged

John - KD8TZC
K1CJS
Member

Posts: 6055




Ignore
« Reply #17 on: April 25, 2013, 10:26:57 AM »

Considering that CB is AM, any decent power supply made for CB will have to be filtered as to not introduce noise on the radio itself.  In any event, they're filtered better than the wall warts are that are so abundant these days!
Logged
K1CJS
Member

Posts: 6055




Ignore
« Reply #18 on: April 26, 2013, 05:04:39 AM »

Sometimes you can get a quieter wall wart from the cable company itself.  Take the old one to the office and talk to a technician there.  Explain what you're looking for and they may be able to get one for you.  You may also try using an old CB power supply--a 12 volt 5 to 7 amp supply.  Simply check the polarity of the connector, cut the wall wart off, and wire up the connector to the supply so the polarity is identical. 
Logged
AF4O
Member

Posts: 23


WWW

Ignore
« Reply #19 on: Today at 10:29:37 AM »

I realize this is an old post but it came up at the top of a google search when i did "rfi cable modem". Just wanted to share my adventures in cable modems. Maybe it will help someone. I was having multiple sometimes strong s8+ birdies across the bands on my FT817, then when i restored a vintage heathkit mohican, i was hearing broadband stuff that sounded like an airplane sitting on a runway especially bad around 4-8mhz but showed up in various other areas in the 2-30mhz range.

Cable modem is an Arris Model: WTM652G that we are leasing (cable modem, 4 connection ethernet, wireless).....through Time Warner. Unplugging AC to it and all of the above goes away. Hooking back up, i unhooked the 4 Ethernet cables from the modem until i unhooked the one going to my daughters emachines computer. That reduced the birdies (not the airplane noise) greatly. Ordered a china SHEILDED 30' ethernet off ebay to replace the thick yellow Belden (yep Belden). And put a type 44 toroid on the computer end 8 turns over the shielded new Ethernet (toroid over the belden did not help). This reduced the strongest birdies to below the noise floor. Think a lot of this was due to the emachines crappy ethernet integrated modem.

Now on to the airplane noise. Tightened the F connector from the coax to the modem securely. Next wrapped aluminium foil over the cable modem (ALL OVER, around the Ethernet cable ends, and all the way up the power cord, the cord was radiating bad) and secured with packing tape. Allowed the wireless duckie to stick out. Put electrical tape around the foil around the AC line cord all the way up to the plug making sure this foil was secured to the modem foil.

Made a braid line about 8' from old rg8 coax with spring loaded large alligator clips to go from my ground system (fairly extensive single point earth ground) to the ground on the F connector and laid some of the braid on top of the modem foil (more on this to follow, how do you attach braid to foil anyway?....). Cut a few narrow slits in the top of the foil to let the modem vent. Then took a empty 5lb whey protein bag which is lined with foil, punch holes in it with a hole punch for venting and slid the entire foiled covered modem in that and took a cable tie and tied it up around the ethernet cables/ac cord. Again allowed the wireless duckie to stick out through a hole. Laid a weight on the bag to touch the foil on the modem and the braid. Whew.... All of this got rid of the vast majority of the airplane noise.

Just wrapping the modem in foil and touching to the F connector sheild got rid of most of the noise. Probably the Arris is poorly shielded and/or is radiating switch mode power junk. This Arris does not have a brick ac adapter just ac power cord going directly to it. I thought about pushing the cable co about getting another modem but after they promised to send one and did not, went this route.

Chuck
AF4O

Logged
Pages: Prev 1 [2]   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!