Message-ID: <001201c29c82$eaf743b0$0700000a@parissn2>
From: "Stewart Nelson" <sn@scgroup.com>
To: rsgb_lf_group@blacksheep.org
References: <12a.1c772615.2b1fe0f8@aol.com>
Date: Thu, 5 Dec 2002 18:22:40 +0100
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Subject: LF: Re: Re: ADSL EMC with LF receiving?
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Hi Markus and all,

Interference to LF reception by DSL:  The +12 dBm figure is total power.
I believe that the spec requires the PSD to be a maximum of -30 dBm/Hz;
looks like my modem is running about -34 dBm/Hz.  It's possible that
some providers run illegal power on noisy lines (sound familiar?).  A
typical CPE ADSL line driver can put out 40 V p-p differential into 100
ohms.  If there are 20 upstream bins, linear operation would entail no
more than 2 V p-p per bin, which corresponds to about -26 dBm/Hz.  The
above figures assume spectral peaks 3 dB above the average.

Even at the higher figure, I would think that with Cat-5 cable from the
modem to where the aerial or underground phone cable enters the house,
you should be fine, as long as your antenna was at least a few meters
from the Cat-5, and you put the DSL low pass filter near the cable entry.
If you still had trouble, I would first suspect the SMPS for the modem!

Interference to DSL downstream from LF Tx:  I agree with Markus that
DSL is very robust; disruption of TCP traffic is extremely unlikely.
If your application is harmed by individual lost packets, e.g. Internet
telephony, then you might lose a little audio each time your Tx keys on :)

73,

Stewart KK7KA

----- Original Message ----- 
From: <MarkusVester@aol.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, December 04, 2002 11:51 PM
Subject: LF: Re: ADSL EMC with LF receiving?


> Hi all,
> 
> most of the messages in this thread have focussed on potential interference 
> from the LF-TX to the ADSL connection. Being digital, I would assume that 
> below a certain threshold there would be no noticable interference at all, 
> and even above that level, error correction protocols and adaptive channel 
> allocation would make it relatively robust.
> 
> However, the emissions from an inadequately shielded ADSL line could be a 
> significant noise source for LF reception. - The background noise level here 
> on a quiet day is around -25dBuV/m in 1Hz, which on the terminals of my 
> Marconi (having -31dB efficiency) is about -107dBm/Hz or -81dBm/4kHz. 
> Stewart's log excerpt indicates a modem power of 12dBm, is that power per 
> channel? If so, the isolation between ADSL and the LF antenna would have to 
> be better than 93dB, which seems fairly demanding. With small receive loops 
> in the vicinity of the wiring, the situation could be even worse.
> 
> As I am still using plain old analog telephony and a V.90 modem here, this is 
> only a rough theoretical estimate, and I wonder if somebody has experienced 
> any problems in actual practice.
> 
> Regards
> Markus, DF6NM