Jim,
> I'm not sure why you think the StationPro causes problems in
> interfacing to amateur equipment.
I'm not saying that StationPro *causes* problems. My point is
that any external device that provides a path for transceiver
supply currents to interact with the mic return will have problems
with modern transceivers.
In actuality, the StationPro does not share any signals or power
with any of a transceiver's microphone connections. It is, in effect,
nothing more than an eight-conductor extension cord (one for each
microphone pin), completely isolated from all desired or undesired
power sources.
That is very similar to the original microHAM microKEYER where the
mic circuit was entirely passive (except for PTT). There were
generally no "RF in the audio" or "hum" problems until someone
connected a microphone modified as recommended by Bob Heil which
connected the mic return to the shell of the Foster plug - then,
of course, all hell broke loose since that connected return currents
back into the mic return. The incorrectly wired Heil AD1 adapters
(Mic and PTT returns reversed) did not help either!
Back in my graduate student days, I worked on experiments involving
voltage measurements of picovolts (measured on materials in a
supercooled liquid helium bath). As you can imagine, keeping track of
the various grounds and signal paths was quite a challenge!
Of course, any shunt path or change in impedance would completely
invalidate a lot of results. Same thing happened with the high VHF
and UHF transmitters when finger stock got dirty in the tuning and
bypass connections. It did not take much to get current into the
wrong place and screw up everything.
In a way I wish amateur manufacturers would go to fully balanced mic
inputs (transformer coupled or balanced instrumentation amplifiers)
along with shielded twisted pair wiring for the audio. If Mic+/Mic-
never touched the chassis (and the shield was connected to chassis
at the entry point) we would not be dealing with any of these issues.
Of course such changes would no longer work with the absurd microphone
wiring practices of some of the biggest manufacturers.
73,
... Joe, W4TV
On 6/7/2013 6:55 PM, Jim Garland wrote:
Joe,
I'm not sure why you think the StationPro causes problems in interfacing to
amateur equipment. The problems a few StationPro builders have encountered
with hum in their microphone circuits have all been traced to improperly
configuring their mic connections. The most common problem has been when a
builder hooks up a vintage mic which uses the shield as the audio return
(along with the PTT return). My little writeup on the topic describes a
workaround for this situation. In actuality, the StationPro does not share
any signals or power with any of a transceiver's microphone connections. It
is, in effect, nothing more than an eight-conductor extension cord (one for
each microphone pin), completely isolated from all desired or undesired
power sources.
That said, I believe your comments about problemmatic RF chokes between the
Mic- line and transceiver ground are well taken, when using audio
accessories which allow microphone leads to share other currents. As I
recall, Elecraft eventually solved their "pin 1" problem by jumpering the RF
choke just inside the front panel, as you suggest. (Incidentally, the
StationPro can be configured, if desired, so that the RF choke can be
jumpered at the transceiver end of the interface cable - at most a few
inches from the transceiver chassis. In some cases this has been a suitable
workaround to the RF choke problem.)
All of these problems are properly called "ground loops," in my opinion,
because they are caused by undesired currents resulting from AC voltage
differences between the transceiver chassis and the chasses of peripheral
equipment. Back in my graduate student days, I worked on experiments
involving voltage measurements of picovolts (measured on materials in a
supercooled liquid helium bath). As you can imagine, keeping track of the
various grounds and signal paths was quite a challenge!
73,
Jim W8ZR
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Joe Subich,
W4TV
Sent: Friday, June 07, 2013 1:16 PM
To: amps@contesting.com
Subject: Re: [Amps] The Pin One Problem
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
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1432 / Virus Database: 3184/5891 - Release Date:
06/07/13
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 10.0.1432 / Virus Database: 3184/5891 - Release Date: 06/07/13
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|