On 8/10/2019 6:09 PM, Paul Randall wrote:
Jim
Double insulated equipment like a laptop charger doesn’t have any
physical access to a metal part that can be bonded to ground. That’s
what double insulated means. Even if the charger has a 3 pin (hot,
neutral and ground) AC connector there is little likelihood that the dc
output side is connected to the ground pin.
That does not change the fact that chassis-to-chassis bonding is good
engineering practice, and audio interconnects should never be depended
on for bonding. One of the reasons that proper bonding is critical to
solve RFI and hum/buzz issies is the Pin One Problem. See my website for
a lot of detail on that, and point your broadcast engineer friend to
that, and to AES48.
In this case using the
laptop for WSJT relies on the connecting wire running from the laptop to
the rig to provide a ground. If that wire is deliberately built to be
isolated then it CAUSES a hum problem rather than avoids one. This is
counter-intuitive and so even though it has nothing to do with software
development, I felt it was worth contributing to the “bad signal”
discussion going on in this forum.
As an aside, I think it very unwise to make a blanket statement that
bonding everything together is good engineering practice.
Sorry, that is a fact.
Someone
reading that may unwittingly bypass a safety ground leakage circuit
breaker by bonding the building’s safety ground to a radio antenna
ground rod. Worse, large AC currents may flow in this connection if the
power utility company uses one of a number of different PME (protective
multiple earth) supply systems where the building’s safety ground is
actually bonded to the neutral supply wire and only to “real” ground
back at the supply transformer.
I suggest that you study the tutorial on grounding and bonding in the
link I posted. And if that isn't sufficient, buy N0AX's recent ARRL book
on Grounding and Bonding, which is largely based on by work, and which
cites the link I posted to it.
Finally, my friend gave a big grin when he read that “The concept of a
so-called "ground loop" is completely false”. He is a professional sound
and television broadcast engineer.
I am a retired audio and broadcast professional, vice-chair of the EMC
Working Group of the Audio Engineering Society Standards Committee,
principal author of all AES Standards on EMC, and a Fellow of the AES.
My first job in Broadcasting was in 1959.
Your broadcast colleague might also want to look at the White Paper on
the topic I was commissioned to write on the topic, as well as the
slides for talks I was hired to give to audio and video contractors and
national conventions. They are in the pro audio section of my website.
There are, indeed, differences in the way power is distributed around
the world, and the White Paper addresses those differences.
"Ground Loops" are a fiction that lead us to wrong solutions to real
problems. Bill Whitlock (also a Fellow of the AES, and with strong RF
chops) correctly identified the real issues, and my advice is based on
his model. I suggest that you study my tutorial material.
73, Jim K9YC
Cheers Paul G3NJV
Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
Windows 10
*From: *Jim Brown <mailto:[email protected]>
*Sent: *08 August 2019 19:20
*To: *[email protected]
<mailto:[email protected]>
*Subject: *Re: [wsjt-devel] 60 Hz + harmonics sidebands on FT8 signals?
(Paul Kube)
The concept of a so-called "ground loop" is completely false. It has no
basis in physics. The "buzz" we hear when equipment is not properly
bonded consists of triplen harmonics of the mains frequency, 50 or 60
Hz, depending on where you live. What DOES couple this trash is the
failure to follow proper engineering practice, which is to bond together
the chassis of every piece of equipment in a system, to bond all grounds
in a building, and to bond that combination of equipment to the
combination of building grounds. (my friends in the UK substitute the
word "earth" for "ground.") A second important part of good practice is
to get power for all interconnected equipment from mains (power) outlets
that have the same Green Wire (protected earth conductor), or whose
green wires are bonded together.
When all of this done, the station is safe for lightning, and no
"isolation" is needed.
Details of proper practice is at http://k9yc.com/GroundingAndAudio.pdf
73, Jim K9YC
On 8/8/2019 3:43 AM, Paul Randall wrote:
> The point of the isolated interface is to prevent noise/hum caused by
> ground loops but if there is no ground at all, it is not only useless
> but actually causes a big problem. I can only assume that if I saw lots
> of 50Hz spurs on receive, there was a good chance they were there on
> transmit as well.
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