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Re: [RFI] RFI from Apple Airport Extreme

To: rfi@contesting.com
Subject: Re: [RFI] RFI from Apple Airport Extreme
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
Date: Fri, 31 Dec 2010 01:50:24 -0500
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>

On 12/30/2010 6:11 PM, doc@kd4e.com wrote:
> Different suggestion ... replace the noisy wall-warts with
> analog ac-dc power supplies.
>> I have 3 Airport Extremes, 2 of the second gen (2.4 or 5 Ghz,
>> 10/100Mbit ether, draft 802.11n) and 1 of the newest (2.4 and 5 Ghz,
>> 10/100/1000 ether, 802.11n).
>> All three use the same power supply, and all three supplies are
>> noisy, dumping common mode noise out both the AC and device sides.
Most of the stuff in the shop that came with wall warts is connected to 
the big 12V supply instead.
I do have a couple connected to the 40A switcher, but it's as quiet as a 
field mouse.
Just be careful and make sure the wall wart is both DC and the voltage 
you want. Not all are 12V and not all are DC.


Roger (K8RI)

>> Noise is classic switcher hash, repeating all the way up past 10m.
>> On 2 of the 3 I have a 2.4in type 31 toroid with 10turns on the AC
>> side (max turns I could fit with a neat winding), and 14turns on
>> another toroid on the output to the AP.
>> This is enough to silence them on 40M and up, on 80M I can still
>> detect, but only when band is totally closed, normal noise floor band
>> open covers them.
>> The third is closer to the antenna (35 feet instead of 60ish for the
>> other 2), and the AC power feed is in a much better position to act
>> as an antenna.  This one has 2 toroids on each side of the PS, and
>> 14turns through a toroid on the ethernet cable leaving the unit.
>> Some folks plug these in and never have an issue, depends on the
>> cabling they connect to.  I happen to have a small space, with the
>> antenna ~ 35 feet from the rear wall of the house, and AC wireing in
>> a great position to play antenna.
>> I would suggest starting by choking both AC and device sides of the
>> PS, and the ethernet run to the broadband unit where it leaves the
>> airport.
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