This morning I spent over an hour trying to work a station on 17-M with no luck. Toward
the end of that effort his signal dropped down into the noise and I
decided to give up the chase. As I was shutting down everything I
noticed an issue.
I have a small program that runs on my
shack computer which communicates with the SPE Expert 2K-FA amplifier over a USB cable. I
can turn the amp ON/OFF, put it into standby, and monitor its front
panel display right from the computer. Today I shut off the amplifier using
that program and then when I closed the program itself, I noticed a
change in the noise level in my receiver. It was a small change but,
nevertheless, it was there. I turned the program back on and the noise
came back.
Below you can see a screenshot from the Audacity program
which is showing the noise from my receiver when switching the program
on and off. The line of numbers
at the top beginning with "0.0", "1.0", "2.0" etc. is seconds.
Beginning just after 1.0 seconds until 4.5 seconds and again at 7.0
until 9.5 seconds, you can see the increased noise level when this
computer program was running. The lower noise displays are when the
program is not running.
It
is not a huge amount of noise, but, it is still there. Adding just
that much noise can at least make it more difficult to copy a weak
station
even if it does not cover up the station. Add this little bit of noise
to the noise generated by other pieces of equipment in the shack and it
all increases the likelihood that you will have difficulty in hearing
the weak ones or it could be enough that you don't hear them at all.
It
is apparent that when this program is running, it is sending data back
and
forth to the amplifier along a USB cable that runs behind my radio.
That data stream is being picked up by the receiver as noise. The noise
is still there with the amplifier off. It is only when the program is
closed that the noise goes away.
Recently I purchased some Snap On Split Bead Ferrites from Palomar Engineers (
http://palomar-engineers.com/)
just for this purpose (image at left.) I purchased a 25-pack of Mix 31
(1-250 MHz)
1/4-inch diameter snap on split beads for $50 and a 10-pack
of Mix 31 (1-250 MHz)
1/2-inch diameter snap on split beads for another $50. Shipping was $10.
I took one
of the 1/4-inch Split Beads and snapped it on the USB cable at the
computer end. (The 1/4-inch ones fit well on Ethernet cables, USB cables, etc.
for a 1-turn choke. The 1/2-inch size will fit RG-8 cables or you can put 3
turns of Ethernet cable through the 1/2-inch ones for more choking if
needed.)
Then,
using the same settings on the receiver (same bandwidth, same band,
same mode, same antenna, etc.) I listened for the noise when turning
that program on and off. The noise could no longer be heard. Just to
make sure I had actually found the problem, I removed the Split Bead
Ferrite Choke from the USB cable and - the noise was back!
This
problem turned out to have an easy fix which cost me $2.20 and about
1-minute of my time. I plan to continue adding Ferrite Chokes to the
computer cables in the shack, the Cable Modem, and to the feedlines to
reduce and/or eliminate any common-mode issues I might have. All these
things add up to keep the noise away from the receiver so it can do its
job and pick out that weak DX. Every little bit helps!
