On 7/11/2012 9:48 AM, Lance Collister, W7GJ wrote: > I am planning to connect the computer LINE OUT to the tip and sleeve of the > KX3 MIC > jack. However, in K9YC's interface manual, he suggests, putting a 4700 ohm > resistor > in series with the tip, and putting a 470 ohm resistor from tip to sleeve. > Has > anyone tried this yet on digital modes with the KX3? Does this provide enough > isolation and prevent hum?
Hi Lance, A clarification. The 4.7K/470 ohm network is a simple 20dB pad (voltage divider), and almost any values in this range and with this ratio will work just fine. Use what's in your junk box. Hum and buzz are caused by leakage currents from the AC mains, which create IR drops in the green wires and other conductors that connect equipment to "ground." Those IR drops are DIFFERENT for each piece of gear because the resistance of the grounding path is different, and, because the connection between gear is unbalanced (that is, one side is connected to the chassis at each end), that DIFFERENCE is added to the signal. The leakage currents are 60 Hz and the harmonics of 60 Hz, and they sound more like buzz (the harmonics) that hum (pure 60 Hz). The solution is VERY simple, but because we have for decades used the wrong words -- "ground loop" -- to describe the problem, is almost always overlooked. That simple solution comes in two steps. 1) Get all power for interconnected equipment from the same AC outlet, or from outlets that share the same "green wire" (that is, they are in the same steel backbox), or from outlets whose green wires are bonded together by short fat copper. 2) Bond from chassis to chassis of all interconnected equipment with short, fat copper. Be sure to complete all this by the long established good engineering practice for safety and lightning protection -- bond from that collection of chassis connections to everything else in your building that's grounded. That tends to help minimize the presence of leakage current on the wiring of our equipment. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
