Date: Sat, 2 Apr 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 #88 To: Ham-Ant Ham-Ant Digest Sat, 2 Apr 94 Volume 94 : Issue 88 Today's Topics: Discone vs 5/8 wave for 2m packet? Homebrew 2M/440 antenna How to base-feed half-wave vertical? (2 msgs) RF leakage from coax? (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: Mon, 28 Mar 1994 16:59:36 GMT From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!sol.ctr.columbia.edu!newsxfer.itd.umich.edu!nntp.cs.ubc.ca!alberta!ve6mgs!mark@network.ucsd.edu Subject: Discone vs 5/8 wave for 2m packet? To: ham-ant@ucsd.edu kcs@rx.uga.edu (Ken Schroder) writes: >I have a 5/8 ground plane availible, which promises something like 3.6 db >gain. I believe that a discone is supposed to be unity gain. 5/8 wave is 3.2 dBq, Discone is 0dBq >So the question is, will there be enough difference between these antennas to >make the trip to the roof worth while? Yes, if not for the gain, the reduced noise on your receiver. A Discone receives *everything* and will overload your radio's front end with pagers and other sources of intermod. >I'd like to put up something bigger or perhaps a beam, but I have covenant >problems and need to stay real low profile. Putting up a beam on packet radio may get you in a lot of hot water, packet works on a cellular coverage basis. If you *must*, to get into a distant repeater in a rural area, but if you are in an urban area, it's far better to put up a good Omni-Directional (I use a Vertical Double-Zepp, 6.3dB gain), than to become just another hidden transmitter ... Ciao, 73 de VE6MGS/Mark -sk- ------------------------------ Date: 1 Apr 1994 01:57:00 GMT From: ihnp4.ucsd.edu!swrinde!cs.utexas.edu!uwm.edu!reuter.cse.ogi.edu!netnews.nwnet.net!bach.seattleu.edu!quick!amc-gw!maunakea!uw-coco!mdisea!usenet@network.ucsd.edu Subject: Homebrew 2M/440 antenna To: ham-ant@ucsd.edu I would like to find a construction article on a dual band (146/440 MHz) antenna. I have seen ones for satellite use but they have separate feedlines for each band. I would like to find a single feedline version for use with a radio which has a built in duplexer. Thanks for the help. Van, KI7AL ------------------------------ Date: 1 Apr 94 10:15:26 -0600 From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!news.ans.net!mrtnt.ntrs.com!tntvax!rs2@network.ucsd.edu Subject: How to base-feed half-wave vertical? To: ham-ant@ucsd.edu I'm looking for advice on the best way to match coax to the bottom of a half-wave vertical. Cushcraft does this for the multi-band R-5 with some type of a proprietary network consisting of toroids, etc. I only want to match a simple 20m half-wave vertical. I'd prefer not to do the match with a "J" type of feed. I'd prefer some type of a matching network. If you have any comments or experience, please let me know. Please answer direct to: -- Richard Steck, W9RS Internet address: steck.richard@ntrs.com Phone: 312-630-6622 Opinions expressed are my own and not those of my employer. ------------------------------ Date: 1 Apr 1994 17:35:15 GMT From: ihnp4.ucsd.edu!swrinde!cs.utexas.edu!math.ohio-state.edu!news.acns.nwu.edu!casbah.acns.nwu.edu!rdewan@network.ucsd.edu Subject: How to base-feed half-wave vertical? To: ham-ant@ucsd.edu In article <1994Apr1.101526.1@tntvax>, Richard Steck, 312-630-6622 wrote: >I'm looking for advice on the best way to match coax to the bottom of a >half-wave vertical. Cushcraft does this for the multi-band R-5 with some type >of a proprietary network consisting of toroids, etc. I only want to match a >simple 20m half-wave vertical. I'd prefer not to do the match with a "J" type >of feed. I'd prefer some type of a matching network. > >If you have any comments or experience, please let me know. Jerry Sevick, W2FMI, in his books and articles offers many solutions in the form of transmission line transformers. Essentially a 16:1 followed by a 4:1 will do the trick. This is approximately the method that Cushcraft uses in the R7. In any case, any matching done should be right at the feed point to keep losses low. The voltages can get quite large. Even with just 100W, the voltage will be in the multi-KV range. Special care and insulation would be required. A much simpler solution would be to be use a tubular element and insert the feed line into the tube at the bootom and feed it in the middle. In this case, you can separate the two halves with a fiber glass tube and use conventional feed or go for a Delta feed inside the tube. Rajiv aa9ch r-dewan@nwu.edu ------------------------------ Date: 31 Mar 1994 20:14:30 GMT From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!darwin.sura.net!udel!news.sprintlink.net!hookup!news.kei.com!news.byu.edu!cwis.isu.edu!u.cc.utah.edu!cs.weber.edu!val@network.ucsd.edu Subject: RF leakage from coax? To: ham-ant@ucsd.edu I know that coaxial cable leaks RF. Why? Coaxial cable leaks with frequencies well below 1GHz, but there are no (easily) visible holes in the braid. Microwave ovens (at 2.8GHz) have doors with 2mm holes that let (significant) light through but (apparently) no (appreciable) radiation. What's up? Do microwave ovens leak but no one has bothered to tell the public that they shouldn't stand in front of them and stare? Or do microwave ovens have the advantage of the shield not being the signal carrier (as with coaxial cable)? Inquiring minds.... - 73 - -=:[ VAL ]:=- -- |================= #include ================/// KB7VBF/P11 =| | "AMIGA: The computer for the creative mind" (tm) Commodore /// Weber State | | "Macintosh: The computer for the rest of us"(tm) Apple \\\/// University | |== "I think, therefore I AMiga" -- val@csulx.weber.edu ==\///= Ogden UT USA =| ------------------------------ Date: Thu, 31 Mar 1994 21:00:22 GMT From: ihnp4.ucsd.edu!library.ucla.edu!agate!howland.reston.ans.net!math.ohio-state.edu!magnus.acs.ohio-state.edu!csn!col.hp.com!srgenprp!alanb@network.ucsd.edu Subject: RF leakage from coax? To: ham-ant@ucsd.edu Val Kartchner (val@cs.weber.edu) wrote: : I know that coaxial cable leaks RF. Why? : Coaxial cable leaks with frequencies well below 1GHz, but there are no : (easily) visible holes in the braid. Sure there are! Good-quality cable is generally specified at 95 % braid coverage and poor-quality cable is much worse. 5% of "hole" is only 26 dB down from 100%. (Yeah, I know braid coverage doesn't equate to dB of leakage, but I'm talking qualitatively here. :=) Note that coax with solid shield has MUCH less leakage than braid-type coax. : Microwave ovens (at 2.8GHz) have : doors with 2mm holes that let (significant) light through but (apparently) : no (appreciable) radiation. What's up? Do microwave ovens leak but no : one has bothered to tell the public that they shouldn't stand in front : of them and stare? Or do microwave ovens have the advantage of the : shield not being the signal carrier (as with coaxial cable)? I think it's partly a matter of how many dB's you care about. If the door of the oven attenuates the 600 watts inside by 40 dB, than only 60 milliwatts leaks out, which won't hurt you. But 40 dB would be inadequate shielding on a sensitive receiver located near powerful sources of interference. AL N1AL ------------------------------ End of Ham-Ant Digest V94 #88 ****************************** ******************************