The AM Forum

For the past several months I've been experiencing extreme interference on 160 to the point where I am unable to operate, particularly right around 1.885.  I took a portable shortwave receiver to help locate the source.  I discovered it was eminating from my next door neighbors home.  Fortunatley, we are friends and they allowed me to probe further.  I discovered the noise is generating from their Verizon DSL provided modem / router combination.  Simply unplugging the wall wart solves the problem.  I am looking for ideas to solve this and keep the peace.  Any suggestions are greatly appreciated.

Try winding as many turns as possible around a ferrite core.

winding what, jim
the power cord/wall wart ?
the rj45 twisted pairs?

 This topic has been discussed before:

 http://amfone.net/Amforum/index.php?topic=4445.0

 Cheap switching supplies are like an RF noise virus..

My DSL modem and the router are in the shack, and never noticed anything on 160 (not that I'm on that band a lot).  The modem is a seperate box, an old unit by Westbell.  Doubt it's the DSL data itself, but if it's coming in your house via the phone line one of those cheap DSL filters at the entry should stop it dead.  I like the switching PS idea, have had a lot of problems with those..  Good luck!  Karl

First congratulations Jay on being able to find the problem and having cooperative neighbors.

You probably need some way of getting RF off the AC power cord.  RF from the appliance is probably using the house wiring as an antenna.  A W3NQN line filter (Array Solutions used to sell them and the may still have them) may work.

More important is to first find out if the wall wart is producing the 160 m. RF (it probably is if it is a switcher).  The very first thing I'd do is find out what current and dc voltage the modem etc. demands and find a linear wall wart supply with the right coaxial DC plug to mate with the DC jack on the appliance.  Swap it in for the stock wall wart and see if the problem goes away.  If it does obviously nothing else needs to be done and you can take the switcher wall wart and blow it up in your back yard.  

If you still have the problem then the RF is from the DSL modem itself and you have to take all the cables in and out of it and put them all through cores (see below).

The ferrite rod solution can be effective.  For the wall wart (I'd first do the linear supply swap or NQN filter above) what you do is get a ferrite rod from a vendor such as Amidon.  Material 31 is a good choice for HF.  If ur problem is only on 160, Material J is good.  These are different mixtures of metals and clay that affect different ranges of frequencies.  wrap as many turns of the wall wart line to the appliance (the low v. DC line), 30 turns or more and tape over the coil with electrical tape.  Something similar can be done with the high v. AC line to the power outlet.

If the DSL modem is the problem get a lot of snap on 1 inch long material 31 beads (mouser sells them) and around ten material J doughnuts from Amidon.   Apply these liberally to all the leads in and out of the DSL modem, looping each line through each doughnut or bead as many times as possible.  This may take some practice and you may need to put in extension lines to get enough wire to loop.  I did this with a cable modem next door to me and it worked (the problem in that case was my 300 w. getting into their modem and not RF from it causing QRM to me though).

One other thing--don't be tempted to save money by buying ferrite beads etc. in bulk.  Vendors such as RF parts sell these and the prices are attractive but notice these deals never specify the material type.  When I was first experimenting with ferrite I got suckered once and wound up with around 10 or 20 snap on split beads that were effective--at 70 MHz and above.  

GL

Rob
K5UJ

Hi Jay,

My father has had Verizon DSL for about 14 months I think, with no complaints of 160 meter interference. 

The modem is about the size of a pack of cigarettes.  I don't recall if there is a separate wall-wart or not.  I will have him e-mail me the modem model number.

Jay,

Quite often it is the power supply itself that is the problem. You may find that the DSL provider has (more expensive) linear supplies, or switching supplies that are appropriately filtered, to resolve these problems. The provider is absolutely responsible for resolving the RF noise issue you are experiencing. I would suggest that you and your neighbor contact Verizon's technical department for assistance. The tier one type reps might not be aware of what needs to be done, but up the line from them will be a technical group that has the background to end the problem.

There was an issue with a switching DC supply raising the noise floor on the input of one of the 6 meter repeaters here in CT and once the right people understood the problem, the DSL provider was very responsive and promptly replaced the offending supply with a filtered one.

In my own house, the little 5VDC 2.5 amp switching supplies for my D-Link router and a USB hub were trashing 160 - 75 meters with loud buzzy oscillations every 60kc that slowly wandered up the band. I replaced both of them with one 5VDC linear supply and that was (thankfully) the end of it.

Good luck! 

My dad's Verizon DSL modem, no RFI :

WESTELL   WIND RIVER
Model F90-610015-06
Rev 14
Made in China
ADSL2+MODEM
 
Model 6100F
 
Logo VERIZON  on surface of modem..
 
Wall wart is 12 VDC.

If the neighbor is up for it, perhaps they can call Verizon and complain.

I've had lots of trouble with AT&T modems and router boxes.

Finally I got a technician to come out to the house -- someone who really understood how things worked, etc.

He ended up replacing the modem and the problem went away -- but first he checked the lines from the AT&T switching box, the balun that converted from twisted pair to coax, all the way to my office where the model is located.

Anyhow, if the neighbor could get a tech to come on site and let you talk to the technician, you might very well get the problem solved.

Swapping out the modem box might well do the trick.

Jay,
Snap on beads work well. See if you can get a couple turns through the bead on every lead coming and going including the power. Might want one on the wall wart end also.

As discussed before as noted by W2NBC, even cable modems have similar problems.  The system here uses modems that have a radiated signal on 154.980, among others, which is the public safety county-wide paging frequency.  So do many of the routers.  Of course, the provider says that it is not their problem since their's is "certified".  Certified as what, nobody knows; broadband transmitter, maybe.

The trouble with putting ferrite beads or making any other kind of change to the neighbors DSL modem yourself is that forever after you will be blamed every time internet access is slow or any Web site they want to goes down or any other kind of unrelated hiccup.

ADSL usually is OK, since it only goes up to 1.1MHz.

ADSL 2+ is another story. The upper downstream tones reach about 2.2MHz, IIRC, it has been a while. But beware, the ethernet cable can also make alot of noise (mostly 7-10-14MHz) and could be conducting the DSL trash out acting like an antenna.

DSL is insidious because it has one tone approximately every 4 KHz. How far are you from the central office or remote CO? The closer, the more noise you will get. It is their responsibility, but you will have to drive them.