From owner-qrp-l@Lehigh.EDU Thu Jul 30 09:07:40 1998 Received: from fidoii.CC.lehigh.EDU (fidoii.CC.lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.8.5/8.8.5) with ESMTP id JAA14364 for ; Thu, 30 Jul 1998 09:07:38 -0400 (EDT) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <12601-14656>; Thu, 30 Jul 1998 09:07:12 -0400 Received: from nss4.cc.Lehigh.EDU ([128.180.1.13]) by fidoii.cc.Lehigh.EDU with ESMTP id <12547-64572>; Thu, 30 Jul 1998 09:05:46 -0400 Received: from mbunix.mitre.org (mbunix.mitre.org [129.83.20.100]) by nss4.cc.Lehigh.EDU (8.8.8/8.8.5) with ESMTP id JAA28282 for ; Thu, 30 Jul 1998 09:05:37 -0400 Received: from TGATE3 (tgate3.mitre.org [129.83.20.27]) by mbunix.mitre.org (8.8.8/8.8.8/mitre.0) with ESMTP id JAA28825 for ; Thu, 30 Jul 1998 09:05:37 -0400 (EDT) Received: from mail09.mitre.org (unverified [129.83.20.43]) by tgate3.mitre.org (EMWAC SMTPRS 0.83) with SMTP id ; Thu, 30 Jul 1998 09:05:36 -0400 Received: by mail09.mitre.org; (5.65v3.2/1.1.8.2/22Jun94-0628PM) id AA12003; Thu, 30 Jul 1998 09:05:45 -0400 Message-Id: <980730090543.25662@mail09.mitre.org.0> Date: Thu, 30 Jul 98 09:05:44 -0400 Reply-To: cjl@mail09.mitre.org Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: cjl@mail09.mitre.org (Charles J. Ludinsky) To: "Low Power Amateur Radio Discussion" Subject: LED SWR indicator X-To: qrp-l@Lehigh.EDU (qrp-l@Lehigh.EDU) X-Mailer: MailWorks 2.0-4 X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO Here's a simple variation on the venerable LED SWR bridge/indicator. The circuit uses a diode voltage doubler to increase overall sensitivity, in conjunction with a superbright LED (Radio Shack part). No toroids to wind, no meters. ---------+-------------------------------------+ XMTR | | ---+ R1 R4 | 50 D1 C1 50 | | 1N270 0.1uF | GND +------|<--------+---------||---------+ | | | | ___ | | LED /^\ RS 276-206 | | | | +------>|--------+---------||---------+------ | D2 C2 ANT R2 1N270 0.1uF +------ 50 | | | +------------------+------------------+ | GND The combination of the voltage doubler circuit and the superbright LED makes this circuit useful down to a few hundred milliwatts. I've tested it with a Pixie2 at about 250mW, and it still allows one to adjust a tuner to an SWR of less than 1.5 to 1 (actually, even better if one adjusts to the center of the "dark" range when tuning). The 1N270 is a high current (compared to a 1N34) Germanium diode. Others, including the common silicon 1N914 will work, but with somewhat less sensitivity. From tests and simulation, this circuit should work OK from a few hundred milliwatts up to two watts, perhaps a little more before something smokes. On the higher end, it's a little harder to adjust since variations in very bright light levels are hard to detect. Regards and 72 DE K1CL, Chuck.