Hmmm....in our neighborhood we certainly have nothing remotely like a 240 v
delta system serving residences, being center tapped and all as mentioned
below.
What we have are moderately high voltage lines - on my street they are at
like 3400 volts, phase to phase. While three phases are available, only two
are run down my street, because that is all they need for our low power use.
Local transformers, that service a couple of houses each, pick off power
from these two primary phases, and produce a center tapped 240 V AC
secondary.
If there were a buzz around here, it sure would not be due to the source
described.
----- Original Message -----
From: "Jim Brown" <k9yc@audiosystemsgroup.com>
To: <Gary@doctorgary.net>; "Discussion of Ten-Tec Equipment"
<tentec@contesting.com>
Sent: Thursday, April 02, 2009 9:13 PM
Subject: Re: [TenTec] Corsair II buzz
Gary Smith wrote:
Thanks
I have noticed the "buzz" on several different power supplies
including a deep cycle battery. It's definitely not a hum but sounds
like something with odd harmonics, a definite buzz.
The most common source of "buzz" consists of "triplen" harmonics of the
AC power line, coupled from the 3-phase power line that is probably
providing your residential service. See my recommendations for bonding
together the gear in your station to kill this noise. Triplen harmonics
are harmonics whose orders are divisible by three -- 180 Hz, 360 Hz, 540
Hz, and so on.
http://audiosystemsgroup.com/RFI-Ham.pdf and
http://audiosystemsgroup.com/HamInterfacing.pdf
The first one is a tutorial in text form that covers a lot of material,
including this. The second is a Power Point that covers much of the same
material.
My solutions are very simple and inexpensive, and don't involve going
inside the radio.
These harmonics are produced in power systems by current flowing at the
peak of the cycle to charge the input filter capacitors in electronic
power supplies (both linear and switchers). Most current cancels in the
neutral (and in the green wires) of 3-phase systems, but triplen
harmonics add. So-called "high leg Delta" power distribution is widely
used in neighborhoods where a few small users need 3-phase but most need
120/240V. It's a 240V Delta, but with one side being center-tapped to
feed residences. This triplen current is the source of what we call
"ground buzz." It's there because there's no neutral feed to those
3-phase users, so all their triplen current goes to ground in the
neutral for residences!
This is yet another reason why it's a very good thing to bond all
grounds together (the most important being lightning). To learn more see
the tutorials.
73,
Jim Brown K9YC
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