[RFI] RF Quiet Laptop for Mobile Console?

Cortland Richmond ka5s at earthlink.net
Fri May 19 04:44:27 EDT 2006

Not long ago, I tried running digital modes using a KAM-XL hooked up to a Fujitsu P5020 "Lifebook" laptop. This actually worked well -- quieter than my e-Machines T2642 -- until I hooked up a power supply.  Both the DC and AC supplies are of course switchers, putting out 16 volts the computer needs.  I am considering tapping off 16 volts from the unregulated part of an analog PS for this application when at home. Meanwhile, carrying an extra battery gives me almost 8 hrs of computer life, and an optional extended-life battery can replace the CD-drive  for (IIRC) about 11 hours total, if that can be accepted. 

I have not gotten "a round tuit," but I suspect the computer might still work on 12 volts, if not charge the battery from it; the battery voltage is only 10.8 volts.  Some years ago there was an article in a Ham magazine about one Amateur who modified a laptop's battery to accept 12 volts. Among other things, this required adding a voltage regulator inside a battery pack.  Alternatively, there is a Ham (name, call forgotten) who builds and sells RF-quiet switching power supplies for such applications.  Or you can yourself shield and filter one built by the computer manufacturer.

I am a member of the IEEE emc-pstc mailing list; very recently there was a posting to that list, which is EMI, EMC and Safety design and test professionals, about being unable to find *any* currently sold Class B-compliant computer to use testing other devices to FCC Class B limits.  This has been a real problem for some time, but with the FCC pretty much out of the Part 15 enforcement action (thanks, Congressman!) we are on our own.

When I bought my present laptop, I carried a Yaesu VR-500 receiver into the store and looked at interference the display models generated in the HF region.  The VR-500 in WFM mode has a spectrum display up to 6 MHz wide.  This Fujitsu is  pretty quiet. It is also no longer sold -- and who knows if another of the same model would be as quiet?  Still, I do recommend a portable receiver when shopping for a computer; it can help keep you from buying a real screamer.

Incidentally, energy efficiency regulations are beginning to force analog power supplies off the market.  


-----Original Message-----
>From: doc <kd4e at verizon.net>
>Sent: May 18, 2006 2:12 PM
>To: RFI List <rfi at contesting.com>, tvi-rfi-emi at mailman.qth.net
>Subject: [RFI] RF Quiet Laptop for Mobile Console?
>Can anyone recommend a laptop for this context?
>1.  Sitting on top of a metal box that will house
>     HF & VHF-UHF gear as well as a scanner.
>     (must not radiate tons of RF noise)
>2.  Mobile in a van that will be on some rough roads.
>     (needs to handle dust and vibration well)
>3.  Runs natively from 12vdc.
>Thanks! & 73, doc kd4e  http://bibleseven.com
>Ham Links: http://bibleseven.com/hl.html

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