Date: Wed, 31 Aug 94 04:30:14 PDT From: Ham-Ant Mailing List and Newsgroup Errors-To: Ham-Ant-Errors@UCSD.Edu Reply-To: Ham-Ant@UCSD.Edu Precedence: Bulk Subject: Ham-Ant Digest V94 #289 To: Ham-Ant Ham-Ant Digest Wed, 31 Aug 94 Volume 94 : Issue 289 Today's Topics: 6 meter antenna????HELP!!! Helical antennae : software? sources? Matching 50 ohms to 25 ohms (2 feedlines) (2 msgs) Send Replies or notes for publication to: Send subscription requests to: Problems you can't solve otherwise to brian@ucsd.edu. Archives of past issues of the Ham-Ant Digest are available (by FTP only) from UCSD.Edu in directory "mailarchives/ham-ant". We trust that readers are intelligent enough to realize that all text herein consists of personal comments and does not represent the official policies or positions of any party. Your mileage may vary. So there. ---------------------------------------------------------------------- Date: 30 Aug 1994 16:30:29 GMT From: ihnp4.ucsd.edu!agate!howland.reston.ans.net!europa.eng.gtefsd.com!news.umbc.edu!eff!usenet.ins.cwru.edu!cleveland.Freenet.Edu!ah157@network.ucsd.edu Subject: 6 meter antenna????HELP!!! To: ham-ant@ucsd.edu Coulds soeone reccomend an antenna for 6 meters fm? homemade or bought, any sources or ways to make one./ I tried winding a half wavelength around pvc pipe,one ground and one positive rf but it does not seem to work all that well. leave mail please. rob kb8sqh ------------------------------ Date: 30 Aug 1994 18:14:39 GMT From: livia.rice.edu!udaya@rice.edu Subject: Helical antennae : software? sources? To: ham-ant@ucsd.edu In article <33ug1d$3ua@u.cc.utah.edu>, siddoway@ee.utah.edu (Derick Siddoway) writes: |> |> |> Anyway, does anyone know of some good software for modeling helical |> antennae? Failing that, does anyone know of a good source for some |> equations so I can model them on my own? |> You might want to look up the following: [1] Gel'fand, I. M., Graev, Zueva, N. M., Morozov, A. I., and Solove'ev, 1962, ~Magnetic surfaces of the three path helical magnetic filed excited by a crimped field," Soviet Physics- Technical Physics, Vol. 6, No. 10, pp 852-855. [2] Sensiper, S., 1955, "Elecetromagnetic wave propagation on helical structures, (A review and survey of recent progress)", Feb. 1955, Proceedings of the I. R. E., pp. 148-161. I am sure you can do a compendex search and get more recent references. Clearly, the above two works are dated. However, they might indicate a few pointers to your problem. UB ******************************************************************* Old vortices never die. They only | udaya@caesar.rice.edu lose their curls. | Department of Mechanical | Engg. and Mat. Sci | Rice University ******************************************************************* ------------------------------ Date: Tue, 30 Aug 1994 17:12:34 GMT From: ihnp4.ucsd.edu!galaxy.ucr.edu!library.ucla.edu!europa.eng.gtefsd.com!gatech!swrinde!sdd.hp.com!hp-pcd!hpcvsnz!tomb@network.ucsd.edu Subject: Matching 50 ohms to 25 ohms (2 feedlines) To: ham-ant@ucsd.edu David Feldman (dgf@netcom.com) wrote: : I have a situation where I need to drive two antennas simultaneously from : one feedline. : Is there a way of doing this with a single in-line transformer of some : sort? I'd like to feed the two 50 ohm feedlines into a T connector, and : match a 50 ohm main feedline into this 25 ohm junction. : Ways I can think of: (1) some other feedline matcher as above, (2) a : broadband toroid transformer of 2:1 ratio, (3) a low-Q pi network of : some sort. (4) could be an "L" network; it will be very low Q and moderately wideband with such a small ratio. (2) is misleading: a 2:1 turns ratio is a 4:1 impedance ratio; you want more like a 1.4:1 turns ratio. (1) will indeed work, but may be impractical, depending on the frequency. More on (1): you can use a 1/4 wave section of impedance equal to sqrt(Zin*Zout) or about 35 ohms. Though 35 ohm coax is made, it's not very common. But if your frequency is high enough, you may be able to make a piece yourself from copper pipe and copper wire or tubing. This probably won't be practical for you below 144MHz. (2) is possible; see books on broadband transformers. (4) is quite easy, from my experience; usually a fixed inductor near the optimum and a variable capacitor to tune it in do fine. It should be broader band than most single-band antennas. : The purpose of this arrangement is to easily allow me (by remote control) : to choose antenna 'A', antenna 'B', or 'Both', with a minimal amount of : outside complexity. So the switching isn't quite trivial: you'll want to switch out the matching network if either antenna is driven by itself. Sounds like probably three SPDT switches. Be careful about leaving unterminated stubs in any of the configurations the switches can assume, especially if this is for VHF or above. 73, K7ITM ------------------------------ Date: Tue, 30 Aug 1994 18:38:12 GMT From: ihnp4.ucsd.edu!dog.ee.lbl.gov!overload.lbl.gov!agate!spool.mu.edu!howland.reston.ans.net!math.ohio-state.edu!sdd.hp.com!col.hp.com!srgenprp!alanb@network.ucsd.edu Subject: Matching 50 ohms to 25 ohms (2 feedlines) To: ham-ant@ucsd.edu Tom Bruhns (tomb@lsid.hp.com) wrote: : David Feldman (dgf@netcom.com) wrote: : : I have a situation where I need to drive two antennas simultaneously from : : one feedline. : : Is there a way of doing this with a single in-line transformer of some : : sort? I'd like to feed the two 50 ohm feedlines into a T connector, and : : match a 50 ohm main feedline into this 25 ohm junction. : : Ways I can think of: (1) some other feedline matcher as above, : More on (1): you can use a 1/4 wave section of impedance equal to : sqrt(Zin*Zout) or about 35 ohms. Though 35 ohm coax is made, it's : not very common. But if your frequency is high enough, you may be : able to make a piece yourself from copper pipe and copper wire or : tubing. This probably won't be practical for you below 144MHz. You could also use two 1/4-wave pieces of 75-ohm coax in parallel. The impedance of the resultant 37.5-ohm transmission line will be close enough. Cut the two pieces from the same roll, or measure them to be sure the electrical lengths are identical. AL N1AL ------------------------------ End of Ham-Ant Digest V94 #289 ******************************