----- Original Message ----- From: "Robert Bruninga" <[email protected]> To: <[email protected]> Sent: Friday, September 27, 2013 2:57 PM Subject: [amsat-bb] Helix matching
Why don’t we see simple ¼ wave 75 ohm lines used as a first step in matching a 140 Ohm Helix to 50 ohms? The ¼ wave line would give an easy 112 ohms and then it shouldn’t be that hard to do a little additional construction matching to get to 140? (building a 2.4 GHz pop-out helix that compresses flat for launch) Bob, WB4APR Hi Bob, WA4APR I have built a 10 turns and a 15 turns Helix for 70 cm using the above matching system wich works very well. The characteristic impedance of my 1/4 wave matching line made of coaxial copper tubing is 88 ohm because SQR(150 x 50) = 88 The only adjustement necessary to get a VSWR close to 1 was to slip the reflector back and fort over the boom only a few centimeters to get the right position. In a separate email I have sent to you the building drawing of my Helix antenna for 70 cm and a picture of my feed matching system for 2400 MHz. For 2.4 GHz I believe that the simplest system to match a Helix is to solder many small strips of copper at the beginning of the first turn of the Helix over a lengt of 1/4 turn and adjust the distance of the strips from the reflector plate until the VSWR becomes close to 1 as possible and this is the system I use for the feed of my 2400 MHz 1.2 meters dish (see photo). 73" de i8CVS Domenico _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
