From owner-qrp-l@Lehigh.EDU Thu Jan 15 10:49:16 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 KAA04851 for ; Thu, 15 Jan 1998 10:49:12 -0500 (EST) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <12795-26720>; Thu, 15 Jan 1998 10:46:28 -0500 Received: from nss4.cc.Lehigh.EDU ([128.180.1.13]) by fidoii.cc.Lehigh.EDU with ESMTP id <12657-26720>; Thu, 15 Jan 1998 10:39:06 -0500 Received: from mailhost.infi.net (mailhost.infi.net [208.131.167.6]) by nss4.cc.Lehigh.EDU (8.8.8/8.8.5) with ESMTP id KAA21066 for ; Thu, 15 Jan 1998 10:39:02 -0500 Received: from 4708 (pm1-1.gso.infi.net [208.142.85.1]) by mailhost.infi.net (8.8.8/8.8.8) with ESMTP id KAA26389; Thu, 15 Jan 1998 10:38:57 -0500 (EST) Message-Id: <199801151538.KAA26389@mailhost.infi.net> Date: Thu, 15 Jan 1998 10:01:25 -0500 Reply-To: ae4ic@nr.infi.net Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: "Bob Kellogg" To: "Low Power Amateur Radio Discussion" Subject: Re: Bright Idea Award #1; RG174U; Balun loss; c.w. tone MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-To: , "Low Power Amateur Radio Discussion" X-MSMail-Priority: Normal X-Priority: 3 X-Mailer: Microsoft Internet Mail 4.70.1155 X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO Adrian, I've been doing quite a bit of tuner testing using the method described by Frank Witt in his 1995 QST articles. So, naturally, I have some comments about your balun loss example. You said: ---------- > A while > back, I compared two tuners: A was the old AC5 balanced line job -- TenTec > produced it as a companion to the Argo 505. > Tuner B is a well-bult commercial unit with the balun. > > For measurements, a calibrated wattmeter monitored power fed into the > tuners, and a simple field-strength meter connected to a pick-up wire > outside monitored the field strength. Power into the tuners was kept > constant. A reading was taken with tuner A peaked, then a reading for > tuner B. Then the power to tuner A was backed off until it reached the > f.s. reading for tuner B. Then the difference in dB was calculated. > > The results were interesting: loss in tuner B attributable to the balun, > with a 1:1 SWR obtained on all bands, was: > > 80m = 2.dB; 40m = 1dB; 20m = 1.7dB; 15m = 6.6dB > > I was unable to reach a low SWR with tuner A on 40m, so the 1dB would have > been slight worse since this represents output from tuner A at a 2:1 SWR. IMHO this is a valid test, and certainly does indicate relative efficiency. It is a good way to get a rough idea of tuner performance. There is one limitation, and that is that for each band the tuner is being tested for just one impedance situation -- the one presented by your antenna. If this is the antenna you intend to use, of course, that's fine. I'm not sure the test would be a valid general comparison between the two tuners. It was certainly a valid test with your antenna. > Now, the choice on 15m is obvious. It illustrates the kind of loss that > can occur in the balun assisted tuner. I won't speculate on why it > occurred at this magnitude on 15m. I didn't check 10m. Someone else might make the identical test with their antenna and get considerably different results. Instead of 15M being the poorest band, it might be 40M, for example. I'd judge that the reason test results were so bad for you on 15M is that your antenna presented an impedance that was well out of the range for your balun on that band. > At any rate, the choice is between ease of bandswitching with the > balun-assisted, or the relative gain that occurs along with the messing > around adjusting taps with tuner A. I go for the gain myself. Yep. I guess what I was saying about tuner testing is obvious. A simple test is to use fixed power, then hook a wattmeter, the tuner and a dummy load in series. Measure the power. Then put the wattmeter on the dummy load side of the tuner and measure the power again. The difference in power reading indicates tuner/balun loss. This method has the same limitation as above, but worse. The measurements are being made at 50 ohms impedance. (why use a tuner at all if the antenna system presents 50 ohm impedance?) OTOH, If there are losses indicated with a 50 ohm impedance, we can expect much worse with the typical antenna! 72/73 and CUL, Bob Kellogg, AE4IC, Greensboro, NC Prolably, but not nececelery. -- Benny Hill