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. 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. 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. 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. 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. _______________________________________________ wsjt-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/wsjt-devel
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