[RFI] Modem Hash

[Christopher E. Brown]

On Sun, 3 Oct 2010, rick darwicki wrote:

> With the start of the 160 season I was working on my RX antenna. Could 
> not null a hash that turns out to be coming from my DSL modem. D-Link 
> 2320 with a lot of ferrite and a lot of turns on both the phone line and 
> power cord.I solved the problem of the TX blowing away the modem with 
> all the ferrite.
>
> Noise is S-4 with modem unplugged and S-9 at 40khz wide peaks with modem 
> plugged into wall. Same regardless of plug polarity or outlet I use. 
> Noise is there with telephone line and link to router unplugged.
>
> Trendnet router is also noisy, about an S-unit add with power plugged in.
>
> Any thoughts, cures, try this ideas?
>
> Thanks
>
> Rick, N6PE



Well, the start for an ADSL modem would be 20 - 30 turns of 22 - 24 ga 
around a type 31 2.4 inch toroid on the phone line, at the modem and at 
the NID.

Best situation would be a ADSL2+ splitter at the NID, into the choke, good 
CAT5 dedicated run to the DSL location and second toroid installed behind 
the rj11 plate (or similar).  Helps force the ADSL signaling back into 
balance and rejuces ingress and egress.  Side beni, it improves max sync 
rate on the DSL line as well.




Is the modem power supply a wall wart, or a brick in the middle?


I swapped out my original wall wart supply for an in the middle type of 
matching specs, that way I could wrap chokes on both sides of the 
switching supply, PS to modem and PS to wall.


Failing that, a ISOBAR-ULTRA 6 or 8 outlet has pretty good choking for < 
2MhZ on the last pair of outlets.  I use a number of them, with additional 
chokes on the AC cable to the wall.



My personal setup is NID ADSL splitter, seperate cat5 run to DSL modem. 
Behind plate choke at every rj11 (DSL or analog side), chokes on both the 
DSL run and the analog run leaving the NID.  Chokes on both sides of the 
modem PS, and on the ether cable leaving the modem.  Modem plugs into 
large UPS with single phase 30a rated brick EMI filters (Corcom EMC 
series) inslatted on both input and output.


Pretty much every single cable is choked in my setup.  Took a while but it 
was worth it.  I can pickup the computers/gear with a pickup look or HT 
within 4 - 6 feet, but except for one weak ethernet clock my antennas (25 
and 40 feet from the computers) cannot tell powered up from down (and I 
have alot of gear).