[R-390] Computer RFI and R390s

[Bill Smith]

Hopefully, the noise you hear is from your computer, and not from a
neighbor's or a computer in another room.  In the latter case, you can still
quiet it down.  A neighbor's may be more difficult unless you can gain
access to the equipment.  First, switch off the computer, or any other
suspected source of noise to establish whether that equipment is really the
source of interference.

(1) Keep the display away from your receiver.  The high voltage and high
magnetic fields generated by the monitor are shielded better in newer
models.

(2) Ground everything well.  2nd story grounding situations can be
problematic.

(3) Invest in Radio Shack 273-104 Snap-together chokes.  Wrap several turns
of wires from every connection in and out of the computer as close to the
computer as practical.  If you wish, start by hooking only the minimum
connections to the computer to see if that initially helps noise, then
connect attachments one by one, with and without cores to see whether the
cores help.

(4) Wrap the power cord to the radio equipment through a choke.  Note that
each turn through the choke counts as another choke in the line, so more
turns wrapped through the core the better.

(5) You may need to wrap your antenna coax through a choke.  Yes, noise
signals can travel on the outside of a coaxial cable into the receiver,
especially if you are operating with a high SWR.

(6) Feed the receiver with a balanced line, i.e. a balun at the end of the
coaxial line if you use coax.  This is difficult in a R-390 series receiver
since the center of the balanced input in those receivers is grounded and it
is hard to match the ground point in the receiver to an external ground
without developing a ground loop (and defeating the effort).  You can test
your feed to the receiver by attaching a section of coax to your balun (for
example a ten-foot line from the receiver to a coax switch), and shorting
the open end.  The receiver should fall silent.  If it doesn't, the coax not
working as coax, but is acting as a local antenna and will pick up local
noise such as from your computer.

(7) Start with the simplest combination - a minimum of external connections
to the computer and the receiver.  See if you can minimize noise with that
configuration, then gradually add connections, testing each time to
determine whether noise is added.  Resolve each line before adding the next.

Your receiver will work better overall.

73 de Bill, AB6MT
billsmith@ispwest.com



-----
Original Message -----
From: "Michael Young" <myoung76@bellsouth.net>
To: <r-390@mailman.qth.net>
Sent: Sunday, November 10, 2002 1:35 PM
Subject: [R-390] Computer RFI and R390s


> How do you guys keep out computer hash from your listening/receiving?
> Turning the computer off isn't viable, since one of the programs I use is
a
> RTTY program.
>
> In addition, I am in suburbia so no room for big antennaes.  Just long
wire
> in the attic.  Plus the Radio Shack ferrite core ant that was talked about
> on this forum this summer.
>
> TNX
>
> Mike
>
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