Deni,
The fact remains that you could spend a lot of time applying ferrites and
by-pass caps, as well as line filters, to many computers and related
gadgets, and still have moderate to severe RFI to your ham gear from this
other equipment. (Keep in mind that the majority of readily available
ferrite cores and beads are designed for maximum effectiveness in the VHF
region. You can get ferrite mixes that work well at HF, but you usually
need to find a vendor and order them.) One approach that almost always
works is to REPLACE the blasted switcher power supplies with linear ones.
This is probably easiest to do with wall warts. Simply measure the output
voltages (and take note of the current rating) from an offending wall wart
supply (such as the one for your printer), and either buy or build a linear
replacement. I don't know about suppliers in Europe, but a surplus dealer
here in the States, Marlin P. Jones & Associates, offers a large number of
linear power supplies that could replace offending switcher wall warts. Of
course, if the given device still causes problems after changing to a
linear power supply, then you know that the switcher wasn't the only
culprit.
Computers and monitors are another story, as they usually have internal
power supplies. Note that Astron, MFJ, Alinco, and others, all offer 13.8
VDC switching power supplies for the amateur radio market. I myself have
an Astron RS-30M. These power supplies are DESIGNED to have minimal
emissions in the HF region, the computer ones are not. Neither the US FCC
nor the European IEC standards require significant radiated emissions
control below 25 or 30 MHz. In my opinion, about the best you can do is
stay with top drawer, name brand computing equipment. Those companies have
real EMC compliance departments and they know how to design and build
equipment that has low emission levels. This may not hold true for every
piece of equipment from any of these companies, but it is a general
practice that they usually follow.
Since you live in Europe, any equipment that you buy there should have the
CE mark on its label someplace. That means the unit not only meets the
European standards for emissions (you hope!), but it should be able to
withstand at least 3V/m of RF from your station. Since RF is reciprocal,
whatever it takes to keep 3V of RF out also helps keep internal emissions
from escaping. Several years ago I had heard about some of the lower tier
computer outfits (generally those in SE Asia region) trying to market
computers in Europe that had the CE mark, but which did not meet specs.
That may no longer be true, but I would avoid unfamiliar brands, even if
the prices are attractive.
Good luck. (Note: Just in case anyone is wondering, I have no financial
interest in any supplier named within this posting.)
73, Dale
WA9ENA
"Deni"
<deni1@tiscali.fr To: "Tom Rauch"
<w8ji@contesting.com>, <rfi@contesting.com>
> cc:
Sent by: Subject: Re: [RFI] Quiet Shack
PC Systems?
rfi-bounces@conte
sting.com
03/18/2004 05:34
AM
Tom Rauch wrote:
>> I'm always intrigued by the photos of other peoples shacks with the
>> PC and monitor mounted right in among the radio gear.
>
> Deni,
>
> Every cable and wire in my shack, including power lines, enter
> through a bulk-head feedthrough plate. All of my cable shield
> connections are good. All of my antenna are at least a few hundered
> feet from the shack.
>
> Unless I get a loose cable connection someplace, I can't hear any
> noise or RFI from stuff in my house and I'm in a very quiet location.
>
> Are you sure you don't have poor shield connections or ground loops?
> Are your antennas very close to the shack or do you have common mode
> current problems with antennas?
>
> 73 Tom
>
>> I have a conventional tower and CRT monitor which creates nasty QRM
>> in my HF receivers, I also have a laptop with TFT screen which is
>> not too bad but it's switched mode PSU/Charger is chronic anywhere
>> near my radio.
Hi Tom, well my shack/ antenna layout is less than ideal at present, but I
do know all of my cable screens are good.
I am in the process of setting up in a new location so still thinking about
antennas etc. However, I must say, despite using balanced antennas
(doublets with balanced line feed) from previous locations I have never
been
able to completely eliminate PC to radio RFI. I am aware that most RFI
emanates from the CRT monitor and some are better than others, but I've
owned a few and never been happy with any of them.
I'm also dismayed at the level of rubbish radiated from modern switched
mode
PSU/ chargers, e.g. my recently acquired printer has a terribly noisy
external
PSU supplied as standard, even my electric toothbrush charger is noisy!
Are there any general guidelines available in the quest for a quiet radio
environment?
73, Deni
F5VJC, GM3SKN
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