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*Subject*: R: R: [amsat-bb] phase shift with coax*From*: "i8cvs" <domenico.i8cvs@xxxxxx>*Date*: Wed, 11 Jul 2001 04:13:21 +0200

----- Original Message ----- From: John P. Toscano <tosca005@tc.umn.edu> To: <Stan@Vandiver.com> Cc: i8cvs <domenico.i8cvs@tin.it>; amsat-bb <amsat-bb@AMSAT.Org> Sent: Wednesday, July 11, 2001 1:36 AM Subject: Re: R: [amsat-bb] phase shift with coax > 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.) > Hello John, If the impedance of each antenna is 50 ohm and if i use two 50 ohm feedlines of any lenght but one 1/4 wavelenght longer than the other i get only the phase shift for circular polarization but not the impedance matching. Infact connecting both lines in parallel to a "T" connector i get an impedance of 25 ohm. In order to match 25 ohm to a 50 ohm feed line i need a transformer made by a line 1/4 electrical wavelengt long wich impedance is SQR ( 25 x 50 )= 35 ohm and i have to made it with tubing or using two 75 ohm lines each 1/4 electrical wavelenght long connected in parallel. This is more complicated than to match the impedance using two 75 ohm lines each 1/4 electrical wavelenght long as used with the original phasing harness on the A144-20 T antennas. In this case infact if the antenna impedance is 50 ohm and the 1/4 wavelength transformer line is 75 ohm the transformed impedance emerging to the open end of this line is 100 ohm and two 100 ohms impedances connected in parallel to a "T" connector make a direct 50 ohm mach to the RX/TX 50 ohm line using a very simple and economical soluction. 73 de i8CVS Domenico > 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 > ---- 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**:**Re: R: R: phase shift with coax***From:*John P. Toscano

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

**Re: R: phase shift with coax***From:*John P. Toscano

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