On Fri, 23 Apr 2010 06:04:26 -0400, Tom W8JI wrote: >Pin 7 and 8 are the same connection point.
The ONLY proper connection point for a cable shield is the shielding enclosure. Doing anything else creates what is known in the audio world as a "pin 1 problem," whereby shield current (RF or baseband power- related buzz) can flow on interior "ground buss" wiring, couple into gain stages, and be detected and/or amplified. Since the AES charges non-members for Standards, I've put technical discussions of that Standard, for which I led the writing group, on my website. http://audiosystemsgroup.com/publish.htm IF the cable shield is separate from both signal conductors (that is, hot and return, as in a balanced mic), it's fine to separate return and shield. But if there's only the shield, it MUST go to the chassis. For many years, I didn't own a dedicated ham mic other than a PTT that came with a radio, so I grabbed an RE16 from my stock of recording mics and used that. It worked fine with suitable EQ as long as I made sure that the cable shield went to the chassis, but a rig with a pin 1 problem could experience RFI. Several years ago, I acquired an FT1000MP, and got reports of RF feedback on 75M and 15M. I ran the pin 1 susceptibility test that's described in one of the AES papers that's on my website on that mic connector, and found strong susceptibility with two peaks -- one a broad one that peaked just below 5 MHz and the second that peaked just below 21 MHz. Seven turns of the mic cable around a #31 2.4-in o.d. toroid killed the RFI. MOST ham rigs come with pin 1 problems -- the MP and K3 are not alone. It has taken radio circuit designers a long time to realize that someone outside their own limited world might know something more about RFI than they do, or to even read beyond their world. The guys who worked with me on AES EMC Standards all have serious RF backgrounds. To get back to the original question, the K3 has EXCELLENT good support for unbalanced electret mics. All that is needed is to connect the mic output to the mic input and turn on the bias via the menu. Inside the radio there's a 5.6K resistor from DC+ to the mic output. And there's enough TXEQ to accommodate the frequency response of any decent mic. 73, Jim Brown 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
