At the Little Thompson Observatory in Berthoud, Colorado (starkids.org), we
had a very similar problem with a large irrigation water pump which, yes,
was fenced off and denied access for safety. To make a long story short,
we found the installer had "cheaped out" and did not buy and install the
required RFI filter (the pumps were controlled using high-current PWM
controllers - ripe for RFI). It was flagged as necessary per FCC on the
data sheet, but it cost a bit over $3k, so it was not installed. Once that
was rectified with purchase and installation of the filter - we brought to
the attention of the installers that FCC required it - the RFI problem was
greatly attenuated, but not totally eliminated.
Dave - WØLEV
On Thu, Mar 7, 2024 at 4:24 AM Wes Stewart via RFI <rfi@contesting.com>
wrote:
> Hi Jim,
>
> Thanks for this. My local power is single-phase with a distribution line
> to the west of me and running N-S on poles. From one pole there is a drop
> that goes underground for 200' or so to a pad mounted transformer that
> feeds my neighbor and me. The underground run from there is about 300' to
> my service entrance.
>
> From the same pole there is a line running from there to several miles to
> the west. About 1400' to the west there is a joining line that runs south
> for about 700' to a pumping station for our water co-op. I'm assuming this
> is three phase since there are three transformers on the pole at the
> station and they have some big pumps. The straight line distance to the
> pole is about 2100'. This has been a source of RFI in the past but more at
> 10-12 meters.
>
> I will try sniffing around there however the source could be inside the
> security fence. But the real answer is to build a fire under the power
> company guy, but he has issues with his management that I don't fully
> understand so won't comment on.
> Again, thanks for the insight.
> Wes
>
>
>
> On Wednesday, March 6, 2024 at 02:35:57 PM MST, Jim Brown <
> jim@audiosystemsgroup.com> wrote:
>
> Wes,
>
> This smells like a case that the late Neil Muncy tracked down in several
> different recording studios, including one where I sat next to him as he
> did it.
>
> The mechanism was noise in form of triplen harmonics of 60 Hz on the
> neutral of a single-phase feed from a high-leg delta power system. This
> distribution is widely used in neighborhoods where there are both
> single-phase and relatively low power 3-phase customers. One of the legs
> has a center-tapped transformer, the others don't, and single phase
> customers are fed by it.
>
> Because single phase customers get the neutral and 3-phase customers do
> not, the path to ground for the triplen harmonic current generated by
> 3-phase loads is via that neutral (3-phase delta customers don't get a
> neutral).
>
> The mechanism for triplen harmonics is that loads in modern power
> systems are nearly all non-linear, where load current is dominated by
> capacitor-input PSUs, distortion the sine wave. Triplen harmonics (order
> divided by 3) add in the neutral of 3-phase systems, and it's not
> unusual for neutral current to exceed phase current. Years ago, I
> attended an SBE meeting at the studio of the Chicago Fox station, where
> the Chief Engineer described how they had almost gone off the air, and
> what they had to do to fix it.
>
> In the recording studios, noise coupling was magnetic to single-coil
> guitar pickups, and dynamic mics without corresponding cancellation
> coils. Top line dynamics from EV and Shure, the major US companies, have
> those coils, lower cost ones do not.
>
> In my Chicago shack, I ran into that same mechanism with an end-fed
> top-loaded wire ending in the shack that used on 80 and 160. It coupled
> into the keying circuit from computer to my rig, which was a shielded
> audio cable, and locked the rig into keydown. I solved the problem by
> replacing that keying line with a high quality braid-shielded twisted
> pair, with the shield connected only at the sending end, and pair
> carrying the keying signal. As a test, I verified that this fixed the
> issue up to 17M.
>
> In addition to magnetic coupling as a mechanism, it could be IR drop in
> the grounding and bonding system.
>
> 73, Jim K9YC
>
> On 3/6/2024 12:05 PM, Wes Stewart wrote:
> > To Chris, I have a Sony ICF-SW7600GR that I have tried to use. With the
> > built-in loopstick it is pretty deaf. Local BC is received fine but the
> > only way I can hear the noise in to hold the radio close to the
> > vertical. An interesting, but unexplained, observation is that when I
> > disconnect the coax feeder the noise is reduced. A resistive
> > termination on the antenna made no difference, still lower noise.
> >
> > Really reaching for something, I considered that since the buried
> > powerline to my house runs somewhere under the coax, which is on the
> > ground, and perhaps under some of the radials, there may be some
> > coupling. A stretch I know. I did listen using my 80-meter inverted-V
> > and the noise is still there at greatly reduced strength.
>
>
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--
*Dave - WØLEV*
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