Re: [wsjt-devel] RFI

[Gary H. <Ga...@is...>]

You could check laptops and their power supplies in a friendly laptop shop
(when they are not too busy!), using a portable AM radio.  Tune between
stations.  Hold the radio near the device.  It should be obvious from the
screaming QRM which ones to avoid like the plague.  The same noise-detection
technique works for LED lamps, networking devices, battery chargers, TVs,
desktop PCs, monitors and other potential noise-generators.  Generally
speaking, it's the switchmode PSUs that cause most grief.

Alternatively, you could simply banish switchmode supplies of all types ...
so either get/build a conventional PSU or find a laptop that will work from
the shack 13.8V supply.  Many seem to be rated for 18V or more but I suspect
they might work at 13.8V although their batteries may not charge (don't
quote me on that: you'd need to check for yourself).

Hinson tip: look out for cardboard boxes of PSUs in charity shops.  Either
pick out the bulky/heavy ones, or make an offer for the whole box.  Check
them for safety before use.  Supplies rated for wide-range inputs (e.g.
110-250V without a selector switch) are generally switchmodes.  The flying
leads and special connectors might be worth keeping, even if the PSUs
themselves are junk.  Unregulated supplies typically produce several volts
above their rating off-load and only vaguely approximate the rated voltage
at the rated current ... so avoid powering valuable electronics directly
from them.  Any PSUs that get hot are clearly suspect.  YMMV.

73,
Gary   ZL2iFB

-----Original Message-----
From: Claude Frantz <Cla...@ba...> 
Sent: 17 March 2019 04:40
To: wsj...@li...
Subject: Re: [wsjt-devel] RFI

On 3/15/19 7:54 PM, Jim Brown wrote:

> As others have noted, EVERY conductor is an antenna, and most 
> computers and rigs are built with manufacturing/design defects that 
> couple RF from attached cables inside the the box to cause problems.
> 
> Here is a tutorial on the topic, and an applications note for finding 
> and killing RF noise. The same ferrite techniques for killing noise 
> apply to killing RFI on cables in our stations.

Many thanks for this excellent information, Jim !

I have noticed that the display of laptops and standalone ones, the power
supply of PC's and laptops are often the source of very bad noise.

Where can we find good recommendations about which product to use or to
avoid ? There is many information available about acoustic noise of power
supplies, but nearly none about radiation and electrical noise.

Best wishes,
Claude (DJ0OT)


_______________________________________________
wsjt-devel mailing list
wsj...@li...
https://lists.sourceforge.net/lists/listinfo/wsjt-devel