From owner-qrp-l@Lehigh.EDU Thu Jan 15 01:24:59 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 BAA04027 for ; Thu, 15 Jan 1998 01:24:57 -0500 (EST) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <12799-27132>; Thu, 15 Jan 1998 01:22:08 -0500 Received: from sunflowr.usd.edu ([192.55.228.42]) by fidoii.cc.Lehigh.EDU with SMTP id <12736-23800>; Thu, 15 Jan 1998 01:20:39 -0500 Received: from localhost (aweiss@localhost) by sunflowr.usd.edu (8.6.12/8.6.9) with SMTP id AAA03143 for ; Thu, 15 Jan 1998 00:16:46 -0600 Message-Id: Date: Thu, 15 Jan 1998 00:16:46 -0600 (CST) Reply-To: aweiss@sunflowr.usd.edu Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: Adrian Weiss 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=US-ASCII X-To: QRP-L@listserv.lehigh.edu X-Sender: aweiss@sundance X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO Hi gang: Some misc. comments. 1) Bright Idea Award #1 goes to Mike, KE4HLU, for solving my age-old problem of launching sinkers into orbit with no chance of recovery. His technique: tie a piece of ribbon to the line or sinker. Now, many of you probably will not find this worthy of the Award. But in about 42 years of hamming, this is one of those few that stopped me dead in my mental tracks with its utter simplicity and effectiveness and made me wonder how I ever came to write QRP articles let alone e-mails! So, I stopped at the local Coast-Coast to buy a new sinker to try out the idea -- they didn't have the right kind. Tomorrow, another store... 2) LB W4RNL listed a few comments about which kind of antnena tuner to use for which kind of setup. He drew attention to the fact that, when balanced line is used, a balanced tuner should be used, that is, one in which the feedline is connected to a basic circuit consisting of an inductor in parallel with a capacitor, coupled to the transmitter via a link coil. Various sophistications usually are applied. The link coil is placed in series with a capacitor to ground to substitute for physically adjustable link position and magnitude of mutual coupling, or something like that. The output inductance is center-tapped to ground, and a dual section capacitor, stators to ground is paralleled with it. Taps along the two sides of the inductor permit inserting the balanced line at the right impedance point etc. As LB pointed out, baluns introduce loss, regardless of the circuit in which they appear. The common approach is to feed the output of a "Tee" or "L' or other circuit to a 4:1 balun, and connect the feedline to the "balanced" side of the balun (remember where the term came from - "balanced to unbalanced"). One inherent problem in this setup is: what is the "4" being transformed down to the "1", which is presumably somewhere in the range which the unbalanced-to-unbalanced circuit can handle. Another problem is the nature of the "4" -- if it were a purely resistive impedance, not too much of a problem. But it is a complex impedance. The balun transforms the reactive component as well as the resistive component, i.e., the "R" and the "+/-j". Bear in mind that the balun is actually a compressed version of a transmission line made possible by the "magnification" aaspect of the toroid core material, i.e., you only need 11t on a core, but 23 air-wound. Now, if you check what happens to the "+/-j" on typical graphs of xmsn lines terminated in such and such a load, you'll notice that near the quarter-wave points, the +/-j component varies enormously, although fairly smooth for the rest of the run. The point is that once you connect the balanced line to the balun, you can end up with a really "wild" complex impedance. Oftentimes, you can still achieve a low SWR -- even a 1:1 with a balun-assisted "Tee" or such. But, what is actually happening is that the balun is dissipating the reflected energy in the core. MOre knowledgeable types out there -- feel free to correct me on this explanation of the theory. In any event, the real question is: "How much loss?". It varies, of course. The toroid core material sets the lower/upper frequency limits across which the balun will function as a transmission line. The impedance at the end of the transmission line varies on different bands. etc. The only way to determine the actual loss is by measurement. One could do this in the lab -- feeding various combination of resistors/capacitors to simulate transmission-line impedances, and measure inputs vs. outputs. I've always preferred the outdoors method using field-strength measurements because I'm really interested in radiated power. 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. I've never liked the thing for two reasons: 1) the taps on the inductor are spaced 5-turns -- and 5 turns is a whole lot of inductance! Not much finesse in fine-tapping here! So, I resorted to squeezing the tips of two paper clips between turns to get the fine-tapping that is usually needed -- hoping that the aligator-clip leads wouldn't pull them out from their rather tenuous locations. 2) for some reason, TenTec got around the link-coil coupling by connecting the input coax across the center 5 turns. This adds to the lack of fine-tuning -- you either get the right combination of paper-clip insertion and parallel capacitor tap points, or you live with a 2:1 SWR. 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. 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. 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. On copying c.w. -- I watched the old 160-hound Ernier K1PBW many times copy DX signals that I could not hear. In fact, when I worked a DX-pedition on Heard Island or somewhere on 160m back in the late '60s, I could not even tell that a signal was present in the mud. He copied them over my shoulder and told me when to go. His explanation: you don't listen for a tone. You detune your auditory perceptors and listen to the noise. It is a different "color" when the dots and dashes are there. I try that all the time -- sometimes it works and sometimes it doesn't. For example, last night I knew there was a FOX and when he was transmitting, but I rarely ever heard a tone. Didn't make any difference -- I couldn't copy! 73 all Ade W0RSP