Yuri,
Your noise problem sounds a lot like one that plagued me for most of the
past several months. In my case, here are the details:
1. The noise affected 160 thru 40 meters the most, but was audible on all
HF bands. I do not have any HF beam, but I do have 2 HF wire antennas.
The noise was worse on the antenna that runs E-W, meaning that the source
was most likely north or south of me.
2. I do have a 6 element yagi on 6m, and could peak the noise as being to
the SE of me using my 6m rig in AM receive mode. The nearest power lines
in that direction are about 3/4 mile away. I did not hear the noise on my
2m SSB receiver, even with 8 elements aimed to the SE. My 6m and 2m
antennas are moe than 80 feet up, so they have a good "view" to the
horizon.
I am telling you this to illustrate the point that K9YC made about
distance between the noise source and your QTH. At HF, noisy power lines
can cause me interference at distances greater than a mile, no problem. As
frequency goes up, spectral density of AC power line noise drops. Thus,
the reason that you must be closer to the source when using VHF detectors
than for HF. As K9YC suggsted, take your 746 on the road, and set it for
AM reception on 2m for best results. For me, 3/4 mile is nearly the limit
I could detect the noise on 6m, and that was too far for 2m detection.
The noise source near me seems to have quit for the time being. If it
stays gone, I'll be happy. Otherwise, if it returns, I'll be out hunting
the source just as you need to do.
Here's a tip that confirmed for me that my noise source was 60 Hz related:
If you happen to have a monitor scope in use on your system to observe
your transmitted waveform, especially when using a linear, consider
connecting that scope to the IF strip in your receiver (or receiver
portion of a transceiver) so that you can observe the INCOMING waveform to
you. Not only does that make it easy to tell why someone has crummy (or
great) audio, it also can help ID the type of interference you are
receiving. My main HF station is a classic Collins S-Line, with the
receiver being a 75S-3. Years ago, I routed the 455 kHz IF output to a
spare rear panel jack and feed that into the amplified and tuned vertical
input of a Heath SB-610 monitor scope. It took me all of about 5 seconds
to confirm that the raspy buzz I was hearing was, indeed, 60 Hz driven.
True, it still did not tell me where the noise source was, but it
certainly helped to confirm the type of source I was after. Note that a
conventional oscilloscope connected to the receiving IF strip in your rig
would also produce the same results, but beware of stray noise pickup in
the scope probe due to its broadbanded nature.
Modern rigs with built-in band scopes might be able to provide some
information. Closely spaced "spikes" across the spectrum to which you are
listening are indicative of power line noise if you can resolve the time
base of the band scope. (Spikes further apart could be indicative of
switching power supply noise, for example.)
Good luck. Let us know what you find.
73, Dale
WA9ENA
"Yuri" <ve3dz@rac.ca>
Sent by: rfi-bounces@contesting.com
08/15/2008 07:48 AM
Please respond to
Yuri <ve3dz@rac.ca>
To
<rfi@contesting.com>
cc
Subject
[RFI] Finding noise source
For a couple of years now, I am suffering from terrible noise at my place
which covers pretty much all HF bands when it's on.
You may listen to it here: http://www.rigexpert.net/noise.wav
The noise seems like a power line one, and it stays on for days, but
sometimes (very seldom though) when I listen to the bands in the morning
before going to work, the noise is not there, which makes me think that
this
might not be the power line noise.
I can easily determine the direction where it's peaking from - my
neighbour's house, but this is also a direction to the street power lines.
Since I only have one tower with rotatable beam (TH6DXX), I decided to
built
4 element 2 m yagi and try to determine the bearing from outside of my
front
yard, using IC746 radio on 2 meters. But, either the sensitivity of the
receiver on 2 meters is not enough, or the noise itself is not strong on 2
meters, I can not tell by looking on S-meter, where the noise is coming
from - S-meter stays on "0" all the time though the noise is still
audible.
The question is, what would you recommend me to use as a "noise finding"
device? I don't really have enough time to build something complicated. I
have to find out either it's power line noise, or the one coming from my
neighbour's.
Thanks in advance for the tips.
Regards,
Yuri VE3DZ
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