I am quite familiar with the issue and while Dr. Garland may call
it a "ground loop", the problem with The W8ZR Station Pro is the
same old problem in interfacing with improperly designed amateur
equipment.
If you bother to look at the schematics for nearly every Yaesu, Icom
or Kenwood transceiver, you will find that the "mic return" connects
to the emitter (discrete transistor preamp) or non-inverting input
(op amp amplifier) of the microphone preamp or amplifier and that
point is connected to the transceiver chassis via an RF choke for
DC.
When the mic return is not *tightly bonded* to the chassis, it causes
currents on the return to find their way to the chassis through the RF
choke and in doing so produces a voltage in series with the mic audio
(I^2*Z). It is not rocket science and not "new." It is amazingly poor
design - one "designer" coping from another - nobody knowing what they
are doing and why. A lot like the blind copying of "floating" grids
in common grid triode amplifiers.
Quite simply, when a transceiver and an audio processing accessory
- whether it be W8ZR's Station Pro or a microHAM microKEYER II -
are connected to a common power supply (at the power supply), some
fraction of the current drawn by the transceiver will return to the
power supply via the connections (PTT return, Computer control return,
mic shield, FSK return, Key return, headphone return, etc.) between
the transceiver and accessory device. Unless *all* of those returns
- *including the mic return* - are terminated to the transceiver
chassis that current will appear across the RF choke (remember the
current varies at at an RF rate) which will act like an old fashioned
choke modulator.
It doesn't take much current through that RF choke to generate enough
modulation to be a problem. Typical audio levels for a microphone
vary from around 5 mV for a dynamic (Kenwood, Yaesu) mic to around
25 mV for an electret (Icom) element.
There are a large number of "band aids" for the design problem in the
amateur transceiver mic inputs. *ALL* of them work by reducing the
current in the returns between the transceiver mic amp and the
accessory. They are as varied as the designer - including reducing
the resistance in the power supply jack on the rig (multiple pins
in parallel), increasing the gauge of the power cord, bonding the
respective chassis together with wide strap, providing power to the
accessory from an *isolated* power supply or from an aux port on the
rig, etc. However, none of them really fix the design flaw in the
transceiver which would generally be as simple as connecting the
mic return directly to the chassis at the mic jack and connecting
a jumper across the offending RF choke.
The amateur manufacturers (except Elecraft, in part) have not learned
what Muncie showed decades ago in professional audio equipment.
73,
... Joe, W4TV
On 6/7/2013 11:38 AM, Carl wrote:
It is obvious that you have drifted off the subject which related to the
Station Pro which Jim thouroughly explained the ground loop issue.
Carl
KM1H
----- Original Message ----- From: "Joe Subich, W4TV" <lists@subich.com>
To: <amps@contesting.com>
Sent: Friday, June 07, 2013 11:12 AM
Subject: Re: [Amps] The Pin One Problem
The problem is that it is not a "Ground loop" - there is no issue
with multiple grounding if the inputs to the device are designed
properly. It occurs only when the signal return is not correctly
connected to the shielded enclosure or bypassed - that also impacts
things like VHF/UHF stability, etc.
If you continue to call it a "ground loop" it is obvious that you
do not understand the nature of the problem. "Pin 1" problem is
as good a term as any since the mechanism for this issue in audio
was first identified in professional equipment using XLR connectors
and the understanding extended to audio equipment with other
connectors (including consumer/prosumer equipment with RCA I/O).
73,
... Joe, W4TV
On 6/7/2013 10:58 AM, Carl wrote:
That would be too easy since ground loops go almost back to prehistory
when many discovered the same thing independently at almos the same
time.
OTOH, before the Brown Theorem it was always called ground loops,
especially in the pro audio industry.
Carl
KM1H
----- Original Message ----- From: "Alex Eban" <alexeban@gmail.com>
To: "'Ian White'" <gm3sek@ifwtech.co.uk>; <amps@contesting.com>
Sent: Friday, June 07, 2013 5:11 AM
Subject: Re: [Amps] The Pin One Problem
What about plain old ground loops, numerology set aside?
Alex 4Z5KS
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Ian White
Sent: Friday, June 07, 2013 9:52 AM
To: amps@contesting.com
Subject: Re: [Amps] The Pin One Problem
K9YC wrote:
When you invent, create, or discover something, you get to name it.
Would that would be "Brown's Law"? I'm sorry, Jim, but it just
ain't so.
We all understand your personal respect for Neil Muncie, but there are
other
overriding priorities such as respect for truth and accuracy.
It is only justifiable to call this "the Pin 1 problem" where that name
accurately applies: specifically to Pin 1 of an XLR connector in the
pro
audio industry. But this problem extends far beyond the area where
it was
originally identified by Neil Muncie. It is no disrespect to insist
that the
more generic problem needs a better name.
Calling it the "Pin 1" problem in situations where it simply isn't
pin 1,
and even where there isn't a connector at all, is a deliberate
falsehood
which misdirects and confuses people. It can only be understood by
someone
who is already initiated into the secret. At so many different levels,
that
is simply A Wrong Thing To Do.
We badly need a short GENERIC name that accurately indicates the
nature of
the problem. That won't be easy to find, but it is something we can
work on.
Calling it the "Pin 1 problem" simply isn't good enough.
73 from Ian GM3SEK
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