Return-Path: Sender: (Marvin Kaye) To: lml Date: Tue, 30 Apr 2002 13:46:02 -0400 Message-ID: X-Original-Return-Path: Received: from [64.38.64.28] (HELO mail1.pe.net) by logan.com (CommuniGate Pro SMTP 3.5.9) with ESMTP id 1203087 for lml@lancaironline.net; Sun, 28 Apr 2002 23:30:50 -0400 Received: from ieee.org (IP-91-245.gst.pe.net [64.38.91.245]) by mail1.pe.net (8.11.6/8.11.3) with ESMTP id g3T3Umv03958 for ; Sun, 28 Apr 2002 20:30:48 -0700 (PDT) X-Original-Message-ID: <3CCCBE51.C9C82CEA@ieee.org> X-Original-Date: Sun, 28 Apr 2002 20:30:25 -0700 From: "Charles R. Patton" Reply-To: charles.r.patton@ieee.org X-Mailer: Mozilla 4.7 [en] (WinNT; U) X-Accept-Language: en,pdf MIME-Version: 1.0 X-Original-To: " (Lancair Mailing List)" Subject: Re: [LML] Transponder Crackling - LNC2 References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit edechazal@comcast.net wrote: > I've become irritated with the crackling noise my transponder (King 76C)... Ed, Some quick thoughts: 1)Make sure its not direct RF by first putting a 50 ohm load instead of the blade antenna on the end of the coax. At that point there should be no TX pulses generated and no VSWR on the coax to couple into other equipment. 2) You mention the ground plane for the blade antenna. Even if the ground plane was bad and causing VSWR, you shouldn't hear "crackling." As the transponder gets interrogated, there would be a buzz, which stops while the radar antenna scans the rest of the circle. So the buzz would repeat every 5 seconds or so in the case of longer distance radar. Airport surveillance radars would repeat faster. 3) Maybe the transponder is randomly self-triggering at a high rate which then causes it to draw current on the battery bus, which might get through the audio amplifiers. 4) I'm not familiar with the King 76C, but if it's a tube type, then there is a high voltage supply, in the multi-hundreds of volts. If there is a leakage path externally on the Hi-V bus, or if a filter capacitor is breaking down, the "sparking" would give rise to wide band interference that might be picked up by audio circuits or even in the RF receivers. 5) If you tap the panel, does the crackling change, i.e., is it microphonic at all? As a troubleshooting technique, take a small, cheap, plastic case (non-shielded in other words) AM radio, tune it to an empty channel, and hold it near the King when it's on. If the AM receiver hears the same noise, you're radiating it from the King. You could check the RF/rx amplifier path by turning off the NAV/COMs and see if the crackling is still there. Also turning off the intercom amp would be another point to check. Regards, Charles R. Patton