Topband: Mysterious Noise - Final

[Tod-ID]

Well, this was a sobering exercise. Every conjecture I came up with was
wrong. The noise is gone and I know exactly what was generating it. Finding
it was a bit serendipitous however.

When I last wrote to the reflector I had found that turning off the circuit
on the 230 vac circuit breaker labeled "pump" stopped the noise. I had
concluded that the noise was generated by the pump controller or maybe the
special meter power company meter attached to the pump circuit at the well
pit. When the temperature finally got above zero C (32 F) I descended into
the pit and searched for the noise source. But, no noise was present in the
pit. I returned to the normal world. Went back to the entry area for power,
cable and telephone. The ground line seemed to have the most noise when I
used the hand held loop to search for it. 

I decided to return to my shop in the basement and look at the spectrum of
the K9AY loop when the pump breaker was on and then off. I got the "ON" scan
and then went upstairs again to turn off the breaker. When I came back down
again I noticed that the power to my station was off !. Naturally, I did not
'hear' any tones and there also were no noise pulses on the spectrum scan.
Suddenly it occurred to me that when the builder had built the house some 45
years ago he had decided to add a few inside the house circuits to the
'pump' circuit. That meant that something connected to one of the 'unusual'
outlets might be causing the noise. 

I rounded up the usual suspects -- wall warts connected to digital devices.
Sure enough the noise vanished even though the pump breaker was active. The
last unit checked [ like a computer program -- the bug is in the last
subroutine you check] was the noise maker. It was a VTech 9114 portable
phone. It has a Class 2 power supply delivering 6vdc at 220 ma. The pulse
train appeared ONLY when the phone was in the cradle charging. The phone
charger cradle did not need to be connected to the telephone line for the
noise to be generated. 

I moved the phone to a different power circuit and the noise vanished. I
tried eliminating the noise pulse by winding several turns of the 6vdc line
from wall wart through a Type 61 ferrite core. That may have reduced the
noise pulse slightly but I am not sure. The fix I have selected for the
moment is to take that phone out of service and replace it with a classic
AT&T desk phone. 

Let me summarize what I think I did wrong in finding the noise. (If I miss
anything feel free to add to this).

1. Once I had localized the source to a single breaker I allowed myself to
assume that only the pump was on that circuit. In defense I would point out
that it was an AC circuit with fairly high amperage which led me to conclude
that only one high current device was attached. I really should have checked
to see if any other powered devices had been turned off at the same time. 

All of the other things I did, including calling the power company, were
driven by this bad assumption.

2. I had not sensed the noise when I walked to the well pit using the
"portable" receiver. This time I 'assumed' that the power line had been
buried so far below ground that I could not pick up the signal. However, I
did not hear the signal when I stood at the top of the well pit yesterday
and thrust the handheld loop into the pit a couple of feet. 

That should have been an alert that the signal was not generated there. 

3. There was a local circuit switch located in the well pit which turned off
the power to the pump for maintenance of the water pump and pressure system.
I should have turned that off with the pump breaker on and I would have
noticed immediately that the noise was NOT associated with the pump and/or
controller.


4. I was finding noise pulse signals everywhere in the house but not more
than about 15 feet from the house. The signals seemed stronger when I moved
the hand held loop near the cable runs and the electrical runs and it was
particularly strong when I checked the line making the earth connection for
the power line. I went out to the power pole and found that the signal,
while present, was much attenuated. 

I should have been more sensitive to the fact that the noise was found close
to the house and not away from the house even when I checked the power line
ground coming from the house.

My thanks to the many folks who wrote with ideas and encouragement. I could
have made this brief and just identified the source, but I felt I owed it to
a few to explain how I had provided insufficient data and misinterpreted
data. Several people had pointed out that if the noise was an orderly pulse
stream with regular periodic breaks and very steady frequencies for the
pulses, then almost certainly the noise was generated by a controlled
digital source rather than by switching power supplies or signal
rectification. 

I certainly hope that what I have written will make noise location and
resolution easier for another reader.

The First Law of Life is => "Trauma Teaches <but it doesn't have to be your
Trauma>"

Tod, K0TO