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Re: [RFI] Noisey PSU (Laptop) on HF Decodeing

To: <k0occ@comcast.net>, "Fred Stevens K2FRD" <k2frd@mac.com>,<RFI@contesting.com>
Subject: Re: [RFI] Noisey PSU (Laptop) on HF Decodeing
From: "Tom Rauch" <w8ji@contesting.com>
Reply-to: Tom Rauch <w8ji@contesting.com>
Date: Tue, 29 May 2007 20:36:17 -0400
List-post: <mailto:rfi@contesting.com>
>I have an IBM laptop model T43 - Not a trace of RFI 
>anywhere - Broadcast band, HF, or VHF.

>> Yes. I have three laptops (old Dell Latitude 300, older 
>> Mac PowerBook 1400,
>> newer Mac iBook 900 [main computer]). All three are RFI 
>> noisy while listening on
>> HF when I have them plugged into commercial power.

>> >Has anyone experienced noise interference from Laptop 
>> >PSU when listening
>> (decoding) HF Signals.

But of course we all know it takes two to tango!!!

Not only must the PS make noise, the noise must somehow get 
into the receiving system.

Every fast efficient switching supply in the world makes 
noise, but how much it bothers our stations depends on our 
antennas as much as it does the supply. It depends on how 
the feedlines are decoupled for common mode, how far the 
antennas are away, the local noise level, the receiver 
bandwidth we use, ambient noise levels around the site, and 
many other things.

Unless you can refer each PS to a uniform measurement 
standard of coupled noise into the power mains, what works 
in one place is largely meaningless somewhere else.

A big problem when using computers for interfaces with 
radios is you are just begging for setting up common mode 
ground loops that aggravate the whole thing, especially when 
a station has a poor wiring layout for ground loops and 
common mode on antenna feedlines.

It is just as important to describe the antenna as it is the 

73 Tom

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