[Top] [All Lists]

Re: [RFI] RF Quiet Laptop for Mobile Console?

To: rfi@contesting.com
Subject: Re: [RFI] RF Quiet Laptop for Mobile Console?
From: doc <kd4e@verizon.net>
Reply-to: kd4e@verizon.net
Date: Mon, 22 May 2006 10:58:11 -0500
List-post: <mailto:rfi@contesting.com>
Thank you thank you!

That is wonderfully helpful information!  I have
saved and printed it for future reference.

I hope that many others are helped by it as well.


>> 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)
> Most ham gear is shielded, and radiates little RF trash. It's the 
> antennas that have the potential for problems. 
>> 3.  Runs natively from 12vdc.
> My IBM T22 and T41 work quite nicely from a Targus 12v universal 
> power supply that I bought several years ago. The T41 lacks a 
> serial port, so I put one of these in it. It works fine. We've 
> used both on two Field Days as our CW logging computers. 
> http://www.bb-elec.com/bb-elec/literature/dsp-100_2103ds.pdf
> At my old QTH, I had several HF antennas within 10 ft of the 
> laptop and never heard RFI on HF. I DID, however, hear trash on 2 
> meters CW or SSB when I moved the mouse or panned the screen when 
> the laptop was powered from AC, and I was never able to suppress 
> it. 
> Expect to do some serious work on your serial interconnection with 
> any computer that you use, because virtually all have pin 1 
> problems, and an antenna as close as in a mobile rig is likely to 
> excite them. A pin 1 problem is when the cable shield (or signal 
> return of an unbalanced circuit) goes to the circuit board rather 
> than to the chassis. To fix it, use the shell of the DB9 as your 
> shield connection and signal rather than pin 5. 
> It also helps a lot to use twisted pair for the serial cable. I 
> recommend CAT5 (or CAT6/7). Shielding helps a bit above about 20 
> MHz, but makes no difference below that. Use one pair for each 
> circuit in the RS-232 connection you are using. For a typical 
> serial connection where only pins 2 and 3 are used for control 
> with pin 5 as the return, use orange for pin 2, blue for pin 3, 
> orange/white and blue/white for return (the shell of the DB9). If 
> your rig(s) require other circuits, use the remaining pairs to 
> connect them. 
> The above precautions will virtually eliminate all RFI from your 
> ham gear to the serial connection. With a "standard" serial cable, 
> my Elecraft K2 would lock up the computer at about 12 watts 
> loading a long wire running a few feet away. With this wiring, I 
> could crank my Ten Tec Titan up to full power (1.5 kW) into the 
> same antenna. 
> I've never heard RFI FROM a serial connection to ham gear, but 
> Ethernet puts out lots of RF trash throughout the HF spectrum, and 
> should be avoided if possible. If you must use it, the RFI app 
> note on my website will tell you how to suppress some of it. 
> Follow the link to Publications. 
> 73,
> Jim Brown K9YC
> http://audiosystemsgroup.com

Thanks! & 73, doc kd4e  http://bibleseven.com
Ham Links: http://bibleseven.com/hl.html
RFI mailing list

<Prev in Thread] Current Thread [Next in Thread>