DSL Modem Interference

[W1RKW]

Anyone have any experience with eliminating DSL modem interference?  

I have a case of it and its all over the 75m band in 70kHz spurs that are about 10kHz wide.  And as luck would have it one spur falls right into the AM window.

I don't know if the phone line is radiating or if the radiation is coming from the box itself, out of the power line or from the network cable.  

I do know the 75m dipole is picking it up and giving about S7 to S8.  Antennas located much further from the station don't seem to hear it but it's there at about an S1 level.

The modem is a 2Wire HG1800 Home Portal.

[W8ER]

Bob,

Yes,  I tried shielding it, no help. I tried a different modem, no help. I went to all Cat5 wiring in the house, no help. I tried bypasses and chokes on the line and relocating it to the garage and putting it on a different circuit, little help.

Then I tried cable. BINGO!   :shock:


--Larry W8ER

[WA1GFZ]

sounds like a switching power supply. Are you sure it is the line?

[W1RKW]

I was gonna say that I'm not so sure it uses a switching power supply.  But I'm wrong. It uses a real dinky little switching supply.  Puts out 6V at 2A.  

Now the question: what can I do to shut it up?

I don't think it's in the line.  I could be radiating from the supply itself.

[WA1GFZ]

put it in a shielded box with feed through filters in and out.

[W1RKW]

stupid question but should I tie the shielded box to ground?

[k4kyv]

I went with cable instead of DSL for that very reason.  It seems inevitable to me that DSL would generate similar problems as BPL, even though on a smaller scale.  The phone wires are closer together and twisted, designed to reduce radiation and pickup, at AUDIO frequencies.  Never designed for  rf or digital transmission and lacking shielding, it is inevitable that there would be some radiation.  Although I never had any great love for cable TV companies, ours does a credible job with high speed internet service and I have been satisfied with them so far.  In addition, I subscribe to the bare-bones basic cable TV, which offers just a little more than what you get with an antenna, for only $2 more a month.

But my cable modem radiates.  I'm not talking about a switching power supply (it has a  wall-wart so I assume it is conventional).  It radiates signals ever 30 kc/s from 80m to beyond the top end of 10m.  It seems to  consist of two carriers, one broken with clicks while the other is pure.  There seems to be some kind of harmonic relationship, as the spacing decreases the lower you go in frequency.  On 80m, the carriers are more like 100~ apart, but by the time you get to 10m, they are about 1 kc/s apart.  The higher you go in frequency, the stronger they get.  If I wanted to try 10m, I would have to unplug the modem.

To hear what this QRM sounds like, click on:
http://ve3hls.tripod.com/noise/noise-files/kc5cmw-modem.mp3

BTW, that's a neat little site for ID'ing some of the mysterious crud that has migrated to the shortwave bands in recent years.  The home page is at:
http://ve3hls.tripod.com/noise/rfihome.html

The first file listed, "My #@^%*&% computer monitor", reminds me of the old LORAN interference on 160m before it was shut down in the early 80's.

[WD8BIL]

Never designed for rf or digital transmission and lacking shielding, it is inevitable that there would be some radiation.

That's a'changin' Don.
We've been working since October to implement the new Telcordia GR1089 Issue 3 specs for rf emissions and immunity that go into effect July 1st of this year. There's a whole slew of new standards limiting emissions from all power and signal I/O ports, including voice lines !!!!

Problem is.... the telecom industry will be spending billions to meet the new specs. Look for even higher phone bills in the near future.

AHHHH...... technology !!!!

[K8SWL]

OK, I've been on DSL for 5 years. Here's what I did, might work for you, no guarantees.
1. Feed the DSL modem direct from the telco service box (don't use an existing phone line). I ran a shielded 2 conductor cable from the telco box through the basement wall directly to the DSL modem (total length about 4 foot). The DSL modm is a Speedstream 5100.
2. I feed a linksys DSL router right next to the DSL modem (again a shielded cable).
3. The router and the DSL modem are both powered by wallwarts. I trashed the walwarts and feed them via a 12 regulated supply. 3 ferrite cores on the power leads.
4. 3 computers in the house are fed via shielded cable from the router.
5. SBC provided in line filters for the telephones. I needed them on one phone as DSL was getting into it when they upgraded me to 3 gig service.

I have noise on 3865 abot 3 Khz wide. 40 and 20 are quiet. There are two points on 10 meters similar to the 3865 noise. Other than that all is clear.


Good luck
Mike K8SWL

[W1RKW]

None of the sounds on the website sound like what I have.   I've been able to determine that it is definitely the tiny switching power supply that came with the modem. The modem itself emits nothing at all.  The phone lines are clean as well. When I wave my hand over the SMPS the signal to the rcvr increases.  Wrapping the DC power lead around my finger increases the interfering signal to the rcvr as well. I found that if I connect the SMPS to an extension cord and lay the top side of the SMPS on top of my PC I eliminate nearly 90% of the RFI.  There's a slight hint of it on 75m and nothing on the rest of the bands.  So some sort of shield is in order.

[W1RKW]

Shielding the modem power supply was a success in eliminating the RFI.  Bands are nice and quiet now.  Thanks for the tips everyone.