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*Subject*: Re: R: [amsat-bb] phase shift with coax*From*: "John P. Toscano" <tosca005@xxxxxxxxxx>*Date*: Tue, 10 Jul 2001 18:36:25 -0500

Stan Vandiver wrote: > > Hi Domenico and all, > > On 10 Jul 2001, at 17:16, i8cvs wrote: > > > As you realize this coax lines uses crimped PL connectors and i see > > that your 10-5/8" measurement refers only to the lengh of the outside > > black jacket of the cable that you see between the crimped ends of > > the PL connector and not to the entire line leght considering in it > > both lenghts of the connector itself . > > These indeed seem to be factory crimped pieces that I have... but > the length that I gave is from tip-to-tip, not just the jacketing > between connectors. Another friend has the same 10-5/8" > dimension tip-to-tip too. So its interesting that your cables are > different. > > Well, I think that I have established that everyone uses the free > space formula for calculating wavelength on this cabling question. > If I have time, I will cut a "long version" (by the formula) and try to > test it out.... or if not, I will just cut to what seems to be the factory > dimensions and run with it. I'm intending to use this antenna > around the end of July for Another pseudo-random thought: You could build a 2-port power divider to do the impedance transformation and not have to deal with the 75 ohm cables. They are a bit expensive to buy, but surprisingly easy to build out of square aluminum tubing for the outside, cut a couple of inches longer than a quarter wavelength, round brass tubing for the inside, cut to exactly a quarter wavelength (velocity factor = 1.0 for air dialectric), three N connectors and a little solder, and some mounting screws for the panel-mount N females. Add a hacksaw, ruler, drill, measuring tape, and soldering iron, and away you go. The ratio of the inside diameter of the square tubing to the outside diameter of the round tubing determines the impedance of the transformer, so the ratio changes depending on whether you're building a 2-port, 3-port, 4-port, etc. power divider. For a 2-port divider, using 1-inch outside width square aluminum stock that is 1/16 of an inch wall thickness, the inside width is 7/8 of an inch. A 1/2 inch outside diameter brass tubing section gives the proper ratio. Of course, since you're in a hurry, you may want to go with the coaxial cable transformer and save the power divider project for another day. (The power divider method still requires you to make two 50-ohm feedlines, one 1/4 wavelength longer than the other, to shift the phase for circular polarity.) Feeding a low-level 146 MHz signal into the whole power divider plus phase shifter assembly, with the two antenna connectors attached to the X and Y inputs of an oscilloscope should give a circular trace if the lengths of the phase shift part of the cabling are correct. If the lengths are a little bit off, the pattern looks like a diagonal ellipse. (Which is why it is called elliptical polarity.) And if the lengths were incorrect by a full quarter wavelength, you'd see that ellipse shrink all the way down to a diagonal line. Performing the same test with only the impedance transformer part of the coax assembly should give the diagonal line if the two 1/4 wavelength sections are the exact same length, though it can't tell you if both sections are too long or too short by the same amount. . . 73 de KB0ZEV ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**Follow-Ups**:**R: R: phase shift with coax***From:*i8cvs

**References**:**Re: R: phase shift with coax***From:*Stan Vandiver

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