[Mobile-Portable] RE: Laptops Near Mobile Rigs

[Hsu, Aaron (NBC Universal)]

>>> I worry about RF noise, especially on HF.

Doc,

You probably won't get much RF noise from the laptop itself as most are
pretty well shielded.  However, the power supply "brick" (or the
internal PS adapter, if the PS is internal to the laptop) is generally a
source of RF hash as they are switching-type supplies.  All the Toshiba
and Compaq power supply "bricks" I've ever used put out a swath of noise
that raises the noise floor on one or two places in each HF band.  By
"one or two places", I mean there's a section with the peak in the
center and noise falling off either side for about 15KHz.  The highest
noise level I've encountered is S7 on the peak.

One option is to run the laptop directly off a battery or the cig
lighter / accessory socket.  Make sure the supply leads to the laptop is
well filtered to prevent the trash from the car's electrical system from
damaging the laptop!  You'll be limited to the 13-14 volts the car
provides - this is generally enough to run the laptop, but it probably
won't allow the laptop to charge the laptop's battery unless your laptop
only requires 12v to start with.  If you have one of the "high-current"
12v cig lighter adapters, check to make sure it isn't a switching
adapter as this will also cause noise.  Just "wire your own" using a
fuse and some choke circuitry.  Also, don't use an DC-AC inverter as
these are switchers and will also generate quite a bit of hash.

Now, the level of hash is subjective.  If there's already a noise source
that's higher than the supplies (or your radio's MDS is higher), you
might not notice anything.  One time at a Field Day event, one of the
stations was using a Samlex switching power supply.  I had my Kenwood
TS-850 hooked up to an Astron RS-35M and was wondering why the noise
floor was S3 (according to the '850) - we were out in the middle of
nowhere and nothing else was on or transmitting except the other radio
with the Samlex supply.  When we turned off the Samlex, the band went
quiet on the '850.  The noise wasn't noticeable on the other radio at
all...probably had a higher MDS and the Samlex's hash level was below
the threshhold.

Anyways, you get the idea.  Good luck with your install!

73,


  - Aaron Hsu, NN6O (ex-KD6DAE)
    {nn6o}@arrl.net
    {aaron.hsu}@nbcuni.com
    No-QRO Int'l #1,000,006
    . -..- - .-. .-   ".... . .- ...- -.--"