Date: Sun, 6 Mar 94 04:30:16 PST 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 #56 To: Ham-Ant Ham-Ant Digest Sun, 6 Mar 94 Volume 94 : Issue 56 Today's Topics: Getting Coax Seal OFF? (2 msgs) MFJ SWR Analyzers (2 msgs) Phasing a loop & vertical Question on the copper tube J-pole (copper cactus) What is the center conductor of RG-59 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: Fri, 4 Mar 1994 06:51:50 GMT From: ihnp4.ucsd.edu!agate!howland.reston.ans.net!usenet.ins.cwru.edu!ncoast!nshore!seastar!paulg@network.ucsd.edu Subject: Getting Coax Seal OFF? To: ham-ant@ucsd.edu woodj@apollo.robins.af.mil writes: > In article , ericr@access3.digex.net (Eric Rosenberg > > > > Can anyone suggest a decent method for taking Coax Seal *off* of a > > connector? It's a mess, and I'm not sure how to do it. > > > > Please email your repsonses... > > > > Thanks -- > > Eric > > > > > > -- > > Eric Rosenberg WD3Q, EI4VPS, ZL0ADG, J20BY, etc. > > 338 14th Street, NE voice: +202-547-3441 > > Washington, DC 20002 USA fax: +202-547-3613 > > ericr@access.digex.com wd3q@amsat.org > > > > I think WD40(tm) will cut it. I don't know know what would be a good cleaner > to remove the WD40... Jim KA4GHX Try Dawn diswashing detergent. THE ** BEST ** non-poluting degreaser around. Rinse with plenty of tap water and allow to air dry. ------------------------------ Date: 5 Mar 94 03:59:55 GMT From: nprdc!ihnp4.ucsd.edu!usc!math.ohio-state.edu!sol.ctr.columbia.edu!news.kei.com!hookup!news.sprintlink.net!connected.com!beauty!rwing!eskimo!bobw@network.ucsd.edu Subject: Getting Coax Seal OFF? To: ham-ant@ucsd.edu Before I "coax-seal" a joint, I wrap the connector with one layer of black electrical tape then cover that with Coax-seal taking care to extend the coax-seal past the electrical tape. This way, if you use quality electrical tape, the only coax-seal to remove is the bit on the coax and the base of the connector as the rest is discarded with the tape. (Cheap tape leaves a gooey residue). -- Bob W. N7UMU ------------------------------ Date: 4 Mar 1994 05:39:07 GMT From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!torn!nott!uotcsi2!hassan@network.ucsd.edu Subject: MFJ SWR Analyzers To: ham-ant@ucsd.edu Doug Braun (dbraun@scdtintel.com) wrote: : In article <1994Mar1.162350.22173@ke4zv.atl.ga.us>, gary@ke4zv.atl.ga.us (Gary Coffman) writes: : : |> No. This only works if the antenna feed point impedance approaches : |> the characteristic impedance of the coax most closely at resonance. : |> That's roughly true for dipoles, but not for some other types of : |> antennas. For example, a 1/4-wave monopole has a feed point impedance : |> at resonance of about 36 ohms. At either side of resonance, the : |> impedance (complex) increases. So there are two points where the : |> impedance will be closer to 50 ohms than the resonant point. : Although the impedance may be closer to 50 ohms, the SWR will : INCREASE. Adding reactive impedance to a resistive load : will NEVER decrease the SWR. Although the total impedance value : may be closer to 50 ohms, the reactive-ness will just make the SWR worse. : Stare at a Smith chart, and you will see this. You are right in your statements but you are wrongly assuming that the load is purely resistive. At least I know for monopoles and dipoles it is rarely so over a broad range of frequencies. Feed point impedance is complex and has both resistive and reactive components. Cancelling the reactive part is one way of improving the SWR but not necessarily to that of 1:1. SWR tuners do more than cancelling the reactive part to make SWR of 1:1. I'm very new in this field but I hope my explanation is O.K, :-) hassan <> ------------------------------ Date: Fri, 4 Mar 1994 17:22:36 GMT From: mvb.saic.com!unogate!news.service.uci.edu!usc!elroy.jpl.nasa.gov!news.msfc.nasa.gov!europa.eng.gtefsd.com!howland.reston.ans.net!math.ohio-state.edu!sdd.hp.com!hp-cv!@@ihnp4.ucsd.edu Subject: MFJ SWR Analyzers To: ham-ant@ucsd.edu Smitty, NA5K, (henrys@netcom.com) wrote: : A general question: Can you dependably determine the resonance of an : antenna by looking for the lowest SWR? To which there has been quite a bit of discussion. I already posted a to-the-point observation about that, but here's some more food for thought: Why do you necessarily _want_ to operate an antenna at resonance? Case-in-point: consider a nominally 1/4 wave radiator above perfect ground, something that can be approached at least with a good ground radial system or a ground plane of wires or (automotive) sheet metal. At resonance, the antenna looks like 30-something ohms (say about 36), purely resistive. Below resonance, the resistive part of the feedpoint impedance drops, and the impedance has a series capacitive reactance. But above resonance (in other words, where the antenna is longer than 1/4 wave), the resistive part rises and the series reactance is inductive. The resistive part increases smoothly, till we get to antiresonance at about 1/2 wave long, where the resistance, highly dependent on diameter/length ratio, will be in the vicinity of 1000 ohms. That means that somewhere a bit longer than 1/4 wave resonance, the resistive part must have passed through 50 ohms. If we can find that point, then we need only put some capacitance in series with the feedpoint to cancel out the inductive part of the antenna feedpoint impedance, and we can get a perfect match to 50 ohms! Now where might we find an installation where there's a ready-made series capacitor? Well, consider thru-glass antennas on cars...if we make the mounting plates the right size to get the right series capacitance, it can exactly cancel the inductance of a 1/4 wave++ radiator. I believe this is quite practical for at least 2 meter installations. See the QST article on thru-glass antennas from about May 93, I think; it doesn't explain _why_ the system works well, but the thoughts here should help you get a better match if you decide to use this system. And in feeding a home-made vertical above a ground system on HF, a variable cap at the base, in series with the feedline, seems like about the simplest of matching networks. 73, K7ITM ------------------------------ Date: Fri, 4 Mar 1994 19:49:20 GMT From: ihnp4.ucsd.edu!newshub.sdsu.edu!ucsnews!sol.ctr.columbia.edu!howland.reston.ans.net!vixen.cso.uiuc.edu!sdd.hp.com!hp-cv!hp-pcd!hpspkla!depaul@network.ucsd.edu Subject: Phasing a loop & vertical To: ham-ant@ucsd.edu Hello Folks. I have an elevated vertical (w/elevated radials) & a 560' horizontal loop. I'm finding that there are times when I use the loop and the vertical in differing combinations I'll get a 2 S unit increase (or decrease) in signal strength. Does anyone know how to vary the energy to the two? A variable L & C network would do the trick, I'm sure...but how do you phase them without mucking up the SWR on the two antennas? Do I need to buy two RF ammeters to see the RF levels going to both? Thanks for your help, Marc DePaul ------------------------------ Date: Fri, 4 Mar 1994 19:44:26 GMT From: ihnp4.ucsd.edu!newshub.sdsu.edu!ucsnews!sol.ctr.columbia.edu!newsxfer.itd.umich.edu!gatech!howland.reston.ans.net!torn!nott!cunews!freenet.carleton.ca!FreeNet.Carleton.CA!ao601@network.ucsd. Subject: Question on the copper tube J-pole (copper cactus) To: ham-ant@ucsd.edu Not so long ago I built a copper J-Pole and had very good results with it. Mine was a 1/2 wave over a 1/2 wave from a plan in 73' mag very easy to make, cheap and when made to the correct dimensions it had a 1.1 to 1 swr. Mine like yours is an omni directional antenna. One hint is to make sure that your antenna's final location is at least 2 wavelengths away from the nearest metal object if at all possible. Good luck with it. Rick VE3IHI ------------------------------ Date: Fri, 4 Mar 94 16:30:48 GMT From: ihnp4.ucsd.edu!mvb.saic.com!unogate!news.service.uci.edu!usc!howland.reston.ans.net!pipex!sunic!psinntp!psinntp!newsserver.pixel.kodak.com!kodak!ornitz@network.ucsd.edu Subject: What is the center conductor of RG-59 To: ham-ant@ucsd.edu In article <2l50t8$i5@bones.et.byu.edu> richard@ee.byu.edu (Richard Christensen) writes: >I noticed the other day that a magnet is attracted to the ceter conductor of >RG 59 coax. What is this stuff? It certainly not copper or aluminum. Remember that RG-59 is now almost a generic term - lots of people make different RG-59 type cable. In the mil-spec version (RG-59B/U MIL-C-17D), the center conductor is #23 copper-clad steel with a resistance of 47 ohms per mile. Variations of RG-59 type cables are often used for CATV and video use that may have solid copper center conductors or may even be stranded for flexibility. 73, Barry WA4VZQ ornitz@kodak.com ------------------------------ Date: Fri, 4 Mar 1994 21:16:46 GMT From: ihnp4.ucsd.edu!pacbell.com!sgiblab!sdd.hp.com!hpscit.sc.hp.com!cupnews0.cup.hp.com!genem@network.ucsd.edu To: ham-ant@ucsd.edu References , , <1994Mar3.170330.27389@nosc.mil>.cup.h Subject : Re: AEA ISOLOOP : While the antenna was fine, we were : having no fun trying to get the thing to tune using that awful set of : controls. Just curious: has anyone out there invested in or used the new controller? You know, the one that's the same price as the antenna? Thanks, Gene -- +----------------------------------------------------------------------------+ |Gene Marshall \-\-\ email: genem@cup.hp.com | |Hewlett Packard Co., MS 42UN | Tel: 408/447-5282 | |Software Svcs & Tech. Division (SST) | ___o Fax: 408/447-5039 | |11000 Wolfe Road L^\<._ AA6IY@N6LDL.CA.USA.NA | |Cupertino, CA 95014 (_)/ (_) CompuServe: 75060,260 | +----------------------------------------------------------------------------+ ------------------------------ Date: Fri, 04 Mar 1994 12:33:51 -0500 From: titan.ksc.nasa.gov!k4dii.ksc.nasa.gov!user@ames.arpa To: ham-ant@ucsd.edu References , <1994Mar1.162350.22173@ke4zv.atl.ga.us>, <2l5mjn$bd5@inews.intel.com>hua. Subject : Re: MFJ SWR Analyzers In article <2l5mjn$bd5@inews.intel.com>, dbraun@scdtintel.com (Doug Braun ) wrote: > Intuitively, the only way to decrease the SWR is to increase the > amount of power that is adsorbed by the load resistance. Adding > reactance in series with the resistance can only decrease the > voltage that the resistance sees, and reduce the power it is adsorbing. Doug and others- I think a subtle point is being missed in this thread: SWR, by basic definition, refers to the characteristic impedance of a given transmission line. Any given antenna might be adjusted to resonance, meaning the reactive component of its impedance is zero. However, the resulting impedance may not equal that of the transmission line. In this resonant case, SWR is defined as the ratio of the load resistance, to the characteristic impedance of the transmission line. (Or its reciprocal, whichever is equal to, or greater than one.) You could use a transmission line as a matching network. For example, suppose you had a 100 Ohm resonant antenna. By using a quarter wave length (times the velocity factor) of 72 Ohm co-ax, you could transform the 100 Ohms to 51.84 Ohms, and run 50 Ohm co-ax from that point back to the transmitter. (Product of the two impedances equals the square of the co-ax impedance.) Not withstanding losses, you would then be transferring maximum power to the load. SWR in the 50 Ohm co-ax is 51.84 divided by 50 = 1.04:1. However, the SWR in the 72 Ohm section of co-ax is still 100 divided by 72 = 1.39:1. 73, Fred, K4DII ------------------------------ End of Ham-Ant Digest V94 #56 ****************************** ******************************