Just a helpful tidbit for anyone working with motor controllers / drives / VFDs
/ frequency drives / etc. (lots of names for the things :-):
The manufacturers usually specify that the wiring between the VFD and the motor
be in conduit. This is to help with EMI/RFI issues. There is usually also a
relatively short maximum reach specified (20-50 feet or so). Obviously they
mean *metal* conduit for shielding, but I've seen electricians use plastic
conduit -- especially for flexible applications -- before.
The flexible conduit is commonly known as "Sealtite" in the trades even though
that is just one manufacturer of the stuff. It's normally a flexible metal
conduit with a plastic outer jacket. There is also an all-plastic version of
the stuff. You can tell them apart by the look and feel once you've seen both,
but another way is that the jacket markings on the "metal inside plastic" kind
will say something about needing to use a separate grounding wire if the
circuit is more than some number of amps. The all-plastic kind will not have
that marking. The reason for the marking is that the steel part of the conduit
is thin and usually can't be a suitable ground connection for safety purposes
for more than 20-30 amps or so.
There is also the usual flexible metal conduit (usually known as greenfield, or
"MC cable" (for "Metal Clad" cable) if it has factory installed wires) which
has a spiral metal outer "jacket" that is conductive.
If your noise source ends up being some kind of motor drive, I'd check to make
sure the wiring between the drive and the motor are in some kind of metal
conduit. It's an easy thing to look for and might also be the cause of the
problem.
-Bill
> -----Original Message-----
> From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of
> Don Kirk
> Sent: Friday, October 24, 2014 2:41 PM
> To: topband
> Subject: Topband: Boradband noise on 160 meters tracked down to
> apartment complex
>
> Recently noticed an increase in my noise level on 160 meters (in the direction
> of my 300 degree pointed pennant), and about 3 weeks ago I tracked it down
> to a new apartment complex which is located 0.41 miles away. Today I
> noticed that the signal had a repeating pattern of approximately 30 minutes
> on and 5 minutes off when listening at my house, so I jumped in the car and
> drove over to the apartment complex to make sure the signal at the
> apartment complex had the same repeating pattern and was in time sync
> with the noise at my house. Thankfully it was, and I made recordings at the
> apartment complex today showing I could predict when the signal would go
> off and come back on based on the time pattern I was following at my house.
>
> I have created a website documenting my direction finding activities for this
> broadband RFI case, and uploaded my prediction recording today. Here is
> the link to my simple website that documents this case :
> http://sites.google.com/site/broadbandrfi/
>
> I contacted the apartment complex today notifying them that I was now
> 100% confident that the broadband noise was originating from their building,
> and will now work with their management to locate the exact source so they
> can follow up with the manufacturer of the equipment for resolution. Based
> on what I have heard so far it sounds like a motor (probably a variable speed
> motor controller), but that's just a guess at this time (sounds like it's
> winding
> up in speed when it first comes on and you can hear this on the recording I
> made at the apartment complex today).
>
> Just FYI, and another very interesting one to track down.
>
> 73,
> Don Kirk (wd8dsb)
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
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