From qrp-l@lehigh.edu Tue Oct 31 12:41:16 1995 Received: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.1/8.7.1) with ESMTP id MAA28984 for ; Tue, 31 Oct 1995 12:41:14 -0500 (EST) Received: from fidoii.cc.lehigh.edu ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <215182-2>; Tue, 31 Oct 1995 12:38:20 EST Message-Id: <9510311734.AA22575@voder.nsc.com> Reply-To: miker@cc.com Originator: qrp-l@lehigh.edu Sender: qrp-l@lehigh.edu Precedence: bulk From: Mike Robinson To: Multiple recipients of list Subject: Homebrew transmatch X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas X-Comment: Low Power Amateur Radio Discussion Date: Tue, 31 Oct 1995 12:37:32 EST Status: RO The nice thing about a QRP transmatch (antenna tuner) is that the capacitors can be fairly compact without worrying about breakdown. The 365pF variable caps that fit in a 2 cubic inch space can typically handle up to 10 watts. And since we NEVER work over 5 watts, this homebrew project will be nice addition to your arsenal without breaking your ham budget. I've built 2 tuners with great success. The first one was a kit from Dan's Small Parts. But to call it a kit is generous. He sent a chassis, 2 variable caps, a 2" PVC fitting the connectors, knobs, some wire and instructions. I had to provide a way to insulate the capacitors from the chassis and also design the configuration of the innards. Also had to drill the holes in the chassis. The exact opposite from an OHR kit. The other tuner was pretty much the same, but I gathered the parts. The circuit design is no secret. It's the standard T-net with 2 variable capacitors and an inductor with selectable taps. The capacitors must be insulated from the chassis. The 1.5"x3"x5.5" plastic box from Radio Shack, works perfectly. Recommended values: 365pF 365pF ||/ ||/ >-----||-------+--------||---------> /|| | /|| ) >-----+ 50uH )<--+ +----> | ) | | | | | | | |---+ | --- --- --- - - - The inductor for my homebrew tuner had it's inductor wound on a plastic 35mm film can. Using 24ga insultated wire, I got about 39 turns. This yields a 36uH inductor which is a little low but seems to tune my favorite bands ok. By the way, the formula for calculating an open air inductor is easy to use. And the resultant inductors are usually very close to the intended values. L = (d^2 * n^2) / (18d + 40len) d is the diameter of the coil n is the total number of turns len is the length of the coil, or n/tpi (turns per inch) Before winding the coil, I stripped a 1/4" section of the insulation about every 13" along the length of the 15' of hookup wire. Once wound, I was able to tap into the coil at very consistent intervals. Not that this matters a whole bunch, but it was an neat way to vary the inductor. Each of the taps then go to an 11 position rotary switch. 2 variable capacitors @ $3ea $6 2 SO-239 connectors @ $2.50e $5 1 plastic box @ $3.49 $4 1 rotary switch @ $1 $1 3 knobs @ $1.99 $2 1 film can 16' of hook up wire Total: $18 I wouldn't recommend using anything smaller than 24ga wire. Remember, we are putting up to 5 watts through that little'ol wire. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 7.3 de Michael aa0ub | QRP: miker@cc.com Norcal #857 CQC #180 | "UR HB 5W FB 72" =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= From qrp-l@lehigh.edu Sat Oct 28 11:39:22 1995 Received: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.1/8.7.1) with ESMTP id LAA01448 for ; Sat, 28 Oct 1995 11:39:16 -0400 (EDT) Received: from fidoii.cc.lehigh.edu ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <215808-1>; Sat, 28 Oct 1995 11:37:15 EDT Message-Id: <951028153440_74740.3166_EHB145-1@CompuServe.COM> Reply-To: 74740.3166@compuserve.com Originator: qrp-l@lehigh.edu Sender: qrp-l@lehigh.edu Precedence: bulk From: Craig LaBarge <74740.3166@compuserve.com> To: Multiple recipients of list Subject: Re: Long Wire Tuner (long) X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas X-Comment: Low Power Amateur Radio Discussion Date: Sat, 28 Oct 1995 11:36:57 EDT Status: RO Here's some info about a little homebrew tuner I use which covers both of the above cases (series and L). 73, Craig WB3GCK --------------------------------------------------------------------------- A SIMPLE AND FLEXIBLE TUNER FOR QRP ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For portable QRP work, I often use either an end-fed half-wavelength wire or a quarter-wavelength wire for an antenna. A simple "L" network (with the antenna attached to the capacitor side) provides a good match for a high-impedance load, such as a half-wavelength wire. A series L-C circuit can be used to match a low-impedance load, as presented by a quarter-wave wire. I wanted to build a simple tuner which could be optimized for either situation with the flick of a switch. Most importantly for me, I wanted to make use of available parts from my junk box. Starting with the typical "L" configuration, I added a DPDT slide switch, as shown in Figure 1. .-------. | SW | | o o-------< ANT L | Figure 1 TX >-*-UUUUUUUUUUUU-----*-----(---o o------+ | ^ | | | |_______| | *---o o | | | | C ----- /// | ----- | | | +--------------------+ With the slide switch in the DOWN position, the configuration is a basic L circuit, as shown in Figure 2. This configuration works well with wires which are multiples of a half-wavelength. Figure 2 TX >---UUUUUUUUUUUU---*---< ANT (HI-Z) | | ----- ----- | /// With the slide switch in the UP position, the inductor and capacitor are now in series, as shown in Figure 3. This configuration works well with a quarter-wavelength long wire. | | Figure 3 TX >---UUUUUUUUUUUU---| |--< ANT (LO-Z) | | The values of the parts aren't particularly critical, but here's what I used: L - 40 turns of #22AWG enameled copper on a plastic 35mm film canister. Tapped in 8 places with a rotary switch to select the taps. C - 220 pf air variable capacitor. The shaft *must* be insulated from the chassis. SW - DPDT slide switch I used an SO-239 jack for the input connection and a binding post for the output connector. If you use two identical connectors for the input and output, you can also reverse the connections and get yet a third configuration shown in Figure 4. Figure 4 TX >--*---UUUUUUUUUUUU----< ANT (LO-Z) | | ----- ----- | /// Antenna tuners (or transmatches) are great projects for the budding homebrewer. They're fairly easy to build from scratch, usually very forgiving with respect to component values, and very useful to have around the shack. While I haven't tested this little tuner on every band with every conceivable load, it has performed well for me on 30 and 40 meters, the bands I use most often in the field. It should do a respectable job on just about any random wire antenna. No scientific breakthrough here. Just a simple antenna tuner with a fair amount of flexibility built in. 73, Craig LaBarge WB3GCK Phoenixville, PA From qrp-l@lehigh.edu Sat Oct 28 11:57:29 1995 Received: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.1/8.7.1) with ESMTP id LAA02045 for ; Sat, 28 Oct 1995 11:57:28 -0400 (EDT) Received: from fidoii.cc.lehigh.edu ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <215819-2>; Sat, 28 Oct 1995 11:57:11 EDT Message-Id: Reply-To: randyw@crl.com Originator: qrp-l@lehigh.edu Sender: qrp-l@lehigh.edu Precedence: bulk From: Steven Wilson To: Multiple recipients of list Subject: Re: Long Wire Tuner (long) X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas X-Comment: Low Power Amateur Radio Discussion In-Reply-To: <951028153440_74740.3166_EHB145-1@CompuServe.COM> Date: Sat, 28 Oct 1995 11:57:08 EDT Status: RO Thanks Craig for the nice info on an easy to build QRP antenna tunner. Hopefully it will be incorporated in some of the new rigs the different fellows construct. I would like to add one usefully modification. Add a #47 lamp in series with the Antenna Output for an RF indicatior. No need for a SWR bridge just tune for maximum RF flow into the antenna. de stan ak0b From qrp-l@lehigh.edu Sat Oct 28 22:36:05 1995 Received: from fidoii.CC.Lehigh.EDU (fidoii.CC.Lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.7.1/8.7.1) with ESMTP id WAA01004 for ; Sat, 28 Oct 1995 22:36:01 -0400 (EDT) Received: from fidoii.cc.lehigh.edu ([127.0.0.1]) by fidoii.cc.lehigh.edu with SMTP id <215725-2>; Sat, 28 Oct 1995 22:35:11 EDT Message-Id: <951028223318_92141650@mail04.mail.aol.com> Reply-To: JCoote@aol.com Originator: qrp-l@lehigh.edu Sender: qrp-l@lehigh.edu Precedence: bulk From: JCoote@aol.com To: Multiple recipients of list Subject: Re: Long Wire Tuner X-Listprocessor-Version: 6.0c -- ListProcessor by Anastasios Kotsikonas X-Comment: Low Power Amateur Radio Discussion Date: Sat, 28 Oct 1995 22:34:34 EDT Status: RO You can make a simple longwire tuner using a single variable capacitor and a single tapped or rotary coil. For 1.8-29 Mhz, values should be 200-350 pF max and 25-30 uH max. The more L/C headroom you have to play with, the more likely you will be able to match a length of wire without pruning on all bands. The tuner is a simple "L" network. The coil is in series with the antenna. The cap is shunt between the antenna and tuner chassis (counterpoise) at the output side of the tuner. You MAY be able to get by with a 350 pF broadcast cap if the rig is CW-only and stays under 5 watts, more power or ssb and you up the RF voltage across the cap, also RF voltage varies with antenna impedance. Other tuners designed for the incorrect practice of force-feeding coax on the wrong band will also work with random wires. Just use a banana plug to the coax center conductor at the tuner output. You can even use a balanced tuner, one balun leg to the wire and the other balun leg to a counterpoise wire (don't ground). I bought an SST tuner and what a pile of doody! The tuner was rated 300 watts, longwires, and 18.-30 Mhz. My 70 watts on 1.9 Mhz melted down the crummy toroid core in the tuner... which was not enough turns to act as a balun below 7 or 10 Mhz. Neon lamps or #47 incandescent lamps will indicate RF in a tuner but brilliance will vary with antenna impedance and current. 4 watts into a wire which is low-Z on 7 mhz might light up the lamp, 4 watts into the same wire (which is high-Z) on 14 Mhz may mean you have to look to see the lamp. Neon lamp hookups may have resistors or one leg not connected due to the high RF voltages involved. #47 and other pilot lamps in series with the antenna lead may require a resistor across the lamp to limit current. Don't worry too much about antenna length. Get a length that works with your tuner on all nine bands. If you have to prune something, start with the counterpoise wire. Happy Stealthing Jay WB6AAM