From owner-qrp-l@Lehigh.EDU Wed Dec 18 07:31:53 1996 Received: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.6/8.7.1) with ESMTP id HAA11837 for ; Wed, 18 Dec 1996 07:31:52 -0500 (EST) X-Received-x: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.6/8.7.1) with ESMTP id HAA11837 for ; Wed, 18 Dec 1996 07:31:52 -0500 (EST) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <35197-51050>; Wed, 18 Dec 1996 07:30:50 -0500 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.lehigh.edu with ESMTP id <34932-43880>; Wed, 18 Dec 1996 07:30:14 -0500 Received: from utkux4.utcc.utk.edu (UTKUX4.UTCC.UTK.EDU [128.169.76.11]) by nss2.CC.Lehigh.EDU (8.8.4/8.8.4) with SMTP id HAA237952 for ; Wed, 18 Dec 1996 07:30:09 -0500 Received: from localhost by utkux4.utcc.utk.edu with SMTP (SMI-8.6/2.7c-UTK) id MAA09060; Wed, 18 Dec 1996 12:29:19 GMT Message-Id: Date: Wed, 18 Dec 1996 07:29:19 -0500 (EST) Reply-To: cebik@utkux.utcc.utk.edu Sender: owner-qrp-l@Lehigh.EDU Precedence: bulk From: "L. B. Cebik" To: "Low Power Amateur Radio Discussion" Subject: Re: Tuners: PIs In-Reply-To: <961217165903_2052250417@emout07.mail.aol.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-To: PaulKB8N@aol.com X-Cc: Low Power Amateur Radio Discussion X-Sender: cebik@utkux4.utcc.utk.edu X-Listprocessor-Version: 8.0 -- ListProcessor(tm) by CREN Status: RO Amen to the PI as an excellent tuner. For QRO, the tuners used to be reversed tube output circuits, which is not really right for antenna use, where there are wide variations in reactance and resistance to be matched. And the voltage on the components also put people off. But at QRP, there is no reason not to use a PI if we use high quality components. If you use that junk box variable capacitor, please be sure it is electrically clean. A continuously variable coil is desirable, since even a PI has inefficient settings. If you must tap and switch, use as many taps as possible. If afraid of suckout, make tuners for low HF and for upper HF to optimize components. Ain't no rule that says an ATU gotta be for all bands or nothing. An L-C-L Tee with coil Q of at least 100 is also good and a low pass filter. Not nearly the loss some folks might assume from seeing 2 coils. I suspect that the following are the chief causes of network tuner losses: 1. Low Q components (inluding old dirty ones, but including as well some cheap ones or badly designed ones); 2. Strays, due to overcramping of components inside metal (especially bad at upper HF with many commercial designs); 3. Bad choice of settings, sometimes forced on us by where the maker chooses to tap the coil(s) or by switched capacitors rather than continuously variable ones. 4. Inadequate range of the antenna-side component, since it does the main work of compensating for the reactance presented by the feedline--it can force some bad settings of the other components. 5. Insufficiently low minimum value of variable capacitors--some in use have as much as 40 pF minimums, when 5-10 pF ought to be common. Just some things to think about with tuners. If you are going to design a PI, design a darn good one--or you won't get the performance that Cecil and Paul have been talking about. -73- LB, W4RNL