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: ADSL modem with RFI immunity?  (Read 1964 times)
G4AON
Member

Posts: 518




Ignore
« on: December 01, 2007, 10:51:16 AM »

For some time I've been using a D-Link DSL-504T. While for the most part it works fine, 80m RF of 20 Watts or more causes the modem to disconnect. Higher frequencies are not a problem. I've tried ferrites, capacitors, etc. with no improvement.

I would like to replace the modem, but don't want to buy something that is no better. Any recommendations for a similar ADSL modem with firewall for UK use?

73 Dave, G4AON
Logged
W3LK
Member

Posts: 5644




Ignore
« Reply #1 on: December 01, 2007, 03:51:23 PM »

A popular modem with the DSL providers here is the Speedstream 4100. I have one on the wall about five feet from the rigs. I have had no problems on any frequency as yet, although I have not had a chance to get the amp on the air in my new house. My HF antenna is a ground-mounted vertical located about 40 feet from the shack.

Many of the problems with RF getting into DSl modems stem from (1) the antenna being too close to the modem and (2) common mode currents on the feed line putting RF into the shack.

Before doing anything else, I'd make sure the shack is RF "clean" and the cables to and from the modem are shielded Cat-5 or better.

Good luck solving the problem.

73,

Lon - W3LK
Naugatuck, Connecticut
Logged

A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
K8KAS
Member

Posts: 569




Ignore
« Reply #2 on: December 02, 2007, 07:07:42 AM »

How good is your station grounded and I mean an RF ground. Check any of the Handbooks and see what it takes to ground a station for RF. My station uses
30---50 foot radials to a copper ground plate, I have no problem running a KW. Where is your antenna located, it should be away from your station/modem.
If you don't have an RF ground and the antenna is over your house you may not be able to clear your problem.
Logged
G4AON
Member

Posts: 518




Ignore
« Reply #3 on: December 02, 2007, 07:33:37 AM »

Guys, with all due respect you are missing the point... My DSL-504T has no problems except on the lower frequencies and no amount of ferrites, station grounding or anything else except running the transmitter into a dummy load makes any difference. A friend has the same ADSL modem with the same problems, these modems are fond of 80m RF (and I guess 160m but we don't operate there).

Nothing else in the house or the shack has a problem with RF and we are talking here of as little as 15 Watts to a dipole, there must be an ADSL router/firewall/modem out there with more RF immunity than the 504 has.

Thanks

Dave
Logged
K7RNV
Member

Posts: 98


WWW

Ignore
« Reply #4 on: December 02, 2007, 09:34:01 AM »

I agree with both hams, speedstream 4100 and rf ground. rf ground is the most important..my set up here in reno nv is the 4100  and i have 2 or more radials in the back yard for rf ground. ground rods are for dc ground not rf..hope this helps
Logged
W3LK
Member

Posts: 5644




Ignore
« Reply #5 on: December 02, 2007, 12:02:12 PM »

<< Guys, with all due respect you are missing the point...>>

No we aren't. We get the point and gave you specific answers that do fit with the problem you are having.

We also observed that the majority of problems of RF getting into the modem is (1) common mode currents on feed lines and (2) poorly shielded cables.

Common mode current problems ARE generally found on the lower bands such as 75/80m. Same deal on connecting cables, the majority of the problems occur on 75/80m.

You asked for a substitute DSL modem and two of us gave you just that.

73,

Lon - W3LK
Naugatuck, Connecticut
Logged

A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
G0HIX
Member

Posts: 2




Ignore
« Reply #6 on: December 04, 2007, 01:25:31 AM »

Dave,

I had the same problem with my ADSL signal being lost whilst transmitting on 80m & 40m - Used a RF-1 filter from K-Y filters:- http://www.merchantamerica.com/kyfilters/ which cleared up my problem.

John is very helpful should you need answers to any questions you may have; and delivery is very quick.

See here for eham reviews:- http://www.eham.net/reviews/detail/2741

Since my review, I have changed to a dipole and can now use max power with no problems at all.

Andy
Logged
G4AON
Member

Posts: 518




Ignore
« Reply #7 on: December 04, 2007, 01:36:24 PM »

Thanks for the very helpful reply Andy. I have a well balanced antenna that produces less RF in the shack (and much less pickup of computer and similar hash) than a conventional coaxial fed dipole with commercial balun that I used to use. The doublet antenna is not far from the house wiring, so hopefully the filter will do the trick. I ordered one this evening.

73 Dave
Logged
G6KIZ
Member

Posts: 34


WWW

Ignore
« Reply #8 on: December 17, 2007, 08:11:43 AM »

I'll be interested to hear how you get on with this.

Unless it is blocking common mode currents only then you are going to have a big problem with the adsl which uses from 25KHz through 1.1 MHz for ADSL and up to 2MHz for ADSL2.

The advert for those filters is talking about modems (down in the audio range) it doesn't say ADSL modems.
Logged
G0HIX
Member

Posts: 2




Ignore
« Reply #9 on: December 18, 2007, 03:45:38 AM »

Mark,

It is hard to find on his site, but he does say it works with DSL:

Model RF-1 (price=$24.95 US Dollars) eradicates HF (short wave 1 to 30 MHz) interference and it works with DSL modems as well as dial-up modems.

Link is: http://www.ky-filters.com/modems.htm

As stated earlier, worked wonders for me and also did not notice any drop in sync speed either.

Andy
Logged
G4AON
Member

Posts: 518




Ignore
« Reply #10 on: December 28, 2007, 04:06:50 AM »

Mark and Andy

I've not been able to fix the problem, however I have improved the situation significantly...

When transmitting on 80m, even at quite low power levels the D-Link DSL-504T tends to signal to the exchange that the link is poor which in turn drops the speed to around 128 Kbs (where it sticks until disconnected overnight)! Adding the RF-1 filter from the K-Y Filter Company doesn't solve the problem, however it seems to have little or no impact on the connection speed either (around 4 M bps).

I've substituted a Linksys AG241 ADSL router/switch for the D-Link one, the Linksys is probably more prone to picking up RF, but the good news is it doesn't seem to signal to the exchange that the line is bad and re-connects in a few seconds at full speed.

I'm not sure how the AG241 manages to pick up RF as with only the DSL connection (via the RF-1 filter) and the mains power via a lot of turns through a ferrite ring close to the AG241, it makes not a jot of difference with as little as ten Watts of RF on 80m knocking out the DSL signal!

At least the connection now recovers without any loss of speed.

Dave
Logged
N6UGY
Member

Posts: 1


WWW

Ignore
« Reply #11 on: February 05, 2010, 07:53:14 PM »

I have 2 KY filters before my Speedstream 5100, and 80 and 160 still knock it offline.  Dennis
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!