Date: Wed, 20 Apr 94 04:30:08 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 #113 To: Ham-Ant Ham-Ant Digest Wed, 20 Apr 94 Volume 94 : Issue 113 Today's Topics: 70cm Parabolic Dish ? About 5/8ths antenna at 900Mhz Formula for determining optimum distance between elements in a Yagi beam GAP verses Butternut Comparison Questions.. Is that all there is to a G5RV? Satellite Receive Dishes Combined in Phase Array Slot antennas on cars? 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: 19 Apr 1994 19:01:15 GMT From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!EU.net!sunic!news.funet.fi!nntp.hut.fi!vipunen.hut.fi!jsi@network.ucsd.edu Subject: 70cm Parabolic Dish To: ham-ant@ucsd.edu In article <1994Apr15.224452.18046@gov.nt.ca> ve8ev@gov.nt.ca (John Boudreau) VE8EV writes: >Is it worthwhile to try to use a 2.5m parabolic dish for 70cm? >It would be used for 70cm EME and also for satellite work. With a good feed you would get about 18.9 dBi gain. In practice this is very hard to accomplish due to considerable blocking. A 2.5m dish is simply too small on 70cm to be a good choice. The gain would be good enough for satellite work but not for EME. Even with a kilowatt you would be able work only a couple of big guys. A single yagi with 5m boom would do the same job. A better choice would be to use it on 23cm or above. With a good system (feed, preamp, PA etc) you would have a "marginal EME station" capable of tens of QSOs on 23cm. Jukka OH6DD ------------------------------ Date: 19 Apr 1994 16:10:31 GMT From: ihnp4.ucsd.edu!swrinde!cs.utexas.edu!math.ohio-state.edu!magnus.acs.ohio-state.edu!csn!col.hp.com!news.dtc.hp.com!hpscit.sc.hp.com!rkarlqu@network.ucsd.edu Subject: ? About 5/8ths antenna at 900Mhz To: ham-ant@ucsd.edu In article <4hgyR_600jWR0SFYwk@andrew.cmu.edu>, Eleen N. Kamas wrote: > > ! > |---> radiator > | > {---> mysterious loading coil > } > | > L--->coax 50 ohm I believe the "coil" is a 180 degree phasing section with a total wire length (not coil length) of 1/2 wave. Works like a 1/4 wave stub (which also has a 1/2 wave of wire). Rick N6RK rkarlqu@scd.hp.com ------------------------------ Date: Tue, 19 Apr 1994 16:35:19 GMT From: ihnp4.ucsd.edu!swrinde!cs.utexas.edu!math.ohio-state.edu!magnus.acs.ohio-state.edu!csn!col.hp.com!fc.hp.com!jayk@network.ucsd.edu Subject: Formula for determining optimum distance between elements in a Yagi beam To: ham-ant@ucsd.edu In article gsladic@mcs.com writes: : >Is there a formula for determining the optimum distances between the driven : >element and the parasitic elements in a yagi beam? : > : >I know the driven element should be a 1/2 wavelength and the reflector 5% : >longer and the director 5% shorter in a 3 element beam. How do I determine : >the distance between the driven element and the parasitic elements? What : >about if the yagi has more than 3 elements, say 7? : Joe Mack (mack@ncifcrf.gov) wrote: : Calculating the spacing between elements is like the multi body : problem and there aren't analytic solutions (that I know of). Satisfactory : answer have only become available since the advent of computers. It is only in : the last 5 years or so (as far as I know) that people could answer : with confidence what the max gain for a yagi of a particular lenght should be. : : The only answers to your questions come from computers, either you : look up tables of designs by people who know what they are doing, or you : buy one of these programs and do it yourself. For yagis I recommend yagiopt : (look in QST, I have no finacial interest in this program), which is : about $100, or NEC, which is free but very difficult to use, or to get your : feet wet, look for mininec, of which there are public domain versions, : or try yagimax (about $25, again I have no financial interest in this program) : which doesn't have the features of yagiopt, but which is cheaper. : good luck : Joe Mack NA3T : mack@ncifcrf.gov If you make a three element yagi as described in the first paragraph it will likely work OK. Using spacings of .1 to .2 wavelength should make a usable yagi. Rough calculations like that will probably get you maybe 75% of maximum gain (for a given boomlength) and who knows how much front-to-back/pattern. But if you want a 'quick and dirty' antenna with some decent gain if should work OK. You could make the boom longer and add some directors that are sightly shorter than the 1st director and improve the gain. Another possibility is to find a proven design, in a book or article, that is to your liking and use that design. As Joe mentioned above a good way to improve design is computer programs. Yagimax is a nice program and is available from several ftp sites. You can change spacings, elements lengths, element sizes and see the effect it has on yagi performance. For pure yagi design I like YagiOptimizer (YO) that Joe mentioned. You can tell the program how you want the yagi to perform (peak the forward gain, peak F/B, or somewhere in between) and it will optimize the design for those parameters. But at $100 it isn't cheap. There are also other programs available that will model wire antennas as well as the yagi. So it all depends on how much effort you want to make. If you want to build a yagi that will perform well it isn't too difficult. If you want to really tweak and optimize a yagi a bit more effort is involved. 73, Jay K0GU jayk@fc.hp.com ------------------------------ Date: 19 Apr 1994 11:14:14 -0400 From: library.ucla.edu!europa.eng.gtefsd.com!howland.reston.ans.net!news.intercon.com!panix!ddsw1!news.kei.com!hookup!news2.sprintlink.net!news.sprintlink.net!redstone.interpath.net@ihnp4.ucsd.edu Subject: GAP verses Butternut Comparison Questions.. To: ham-ant@ucsd.edu In article , wrote: >results are well worth it. The Butternut HF2V is great on 40 and decent on >80, but the GAP just blows it away. I worked DXCC on 80 and 40 with the >GAP, running 100w or less, in a matter of a couple months of very casual >operating. Also, I had no trouble working anything I could hear on 80 and >40. It's so-so on 160, but I still managed to work DX with it. If you >have the room to put it up and the people to help you put it up, go for it. > >73, Mike KB3RG/CU3LF/CU0WPX Mike, Can you tell us more about your DXCC with the Gap. Did you work the DXCC at the CU3LF and CU0WPX QTHs or at you KB3RG QTH? Also if from KB3RG what were your most exotic and most distant QSOs? Congratulations on the 80m DXCC with 100 watts (or was that DXCC combining 80 and 40m). 80m is tough with 100w and any antenna because the DX station often has lots of local QRM on his end. Mike Wood Internet: mikewood@mercury.interpath.net The Signal Group Amateur Radio: NT4O P.O. Box 1979 ***Avoid company disclaimers by owning the company *** Wake Forest, NC 27588 Phone: 919-556-8477 Fax: 919-556-0115 ------------------------------ Date: Tue, 19 Apr 1994 15:16:14 GMT From: world!dts@uunet.uu.net Subject: Is that all there is to a G5RV? To: ham-ant@ucsd.edu In article <2okbac$8eq@chnews.intel.com> cmoore@ilx018.intel.com (Cecil A. Moore -FT-~) writes: >Daniel T Senie (dts@world.std.com) wrote: > >: You've said this before. Did G5RV himself really say that RG58 was >: required? Seems to me that ANY 50 ohm coax could be connected in with >: only one real difference between them, line loss... > >Hi again, Daniel. I guess I didn't make myself clear. What Varney, G5RV, >said in his latest writings is to eliminate the coax and bring the >ladder-line directly to a balanced antenna tuner. Most of the commercially >available G5RVs that I have seen use RG58 so that's why I pick on it. The commercially available G5RV's I've seen use a PL-259 at the bottom of the twin-lead, and let the purchaser add whatever coax they want. We were working from different points of reference, so now I understand the confusion :-). >Obviously, the lower the transmission line loss, the better but 9913 at >50 cents/ft has more than double the loss of ladder-line at 10 cents/ft. Of course the 50 ohm coax plugs into a rig with an auto tuner, and the auto tuners in the various newer rigs will handle a G5RV on all bands 160-10. While use of such a tuner is not necessarily optimal, nor is the use of coax in this setup, I find that a G5RV and a small rig with an auto tuner (eg. FT890) makes an excellent emergency station. It also makes a very good first station for a new ham. I know you're a strong proponent of ladder line. I like the stuff too, but as long as one understands loss factors of different feedlines, and such, the use of coax is often much more convenient. The extra expense of coax is often worth it given the added benefits of routing, burying, and connecting options gained. -- --------------------------------------------------------------- Daniel Senie Internet: dts@world.std.com Daniel Senie Consulting n1jeb@world.std.com 508-779-0439 Compuserve: 74176,1347 ------------------------------ Date: Tue, 19 Apr 1994 11:59:47 GMT From: ncar!csn!boulder!cnsnews!spot.Colorado.EDU!weverka@ames.arpa Subject: Satellite Receive Dishes Combined in Phase Array To: ham-ant@ucsd.edu In article <1994Apr18.125606.21991@kocrsv01.delcoelect.com>, Alan Anderson wrote: >>In <2osk75INN7mv@uwm.edu>, weening@convex.csd.uwm.edu (Richard W Weening): >>> >>>Is anyone aware of successful methods for combining two or more satellite >>>receive dishes in phase array as a means of achieving receive gain >>>comparable to a single larger dish? ^^^^ >> >>I've always seen phased antenna arrays used for more precise pointing, not >>for increased gain. Of course, with a narrower "beam" you GET more gain, >>so maybe it isn't as unusual an idea as it first seemed.... >> phased array antennas are commonly used to acheive gain. In article , Joe Mack wrote: > COmbinng antennas into arrays is covered in most texts on antennas. You >will have to do it at receive frequency and feed the power to a combiner. The >pointing accuracy needed will be approx that for an antenna with the diam= >spacing between the two dishes (ie you'll need to be very accurate), while >the signal will only go up 3bd. This is great for radia astronomy where you >want to know exactly where your source is. However you just want more >signal, in which case it will be easier to buy a bigger dish. > You don't have to point the individual antennas in an array any better than you would have to point them by them selves. You do have to match the line lengths from the antennas to the power combiner at the higher pointing accuracy, but this is relatively easy. In fact with a variable line length you can steer the combined beam anywhere within the main beam of the single dish. You don't have to combine the signals at the carrier frequency either, if the two downconverters are driven by the same local oscilator. A high frequency power combiner might be cheap than two down converters. Whether a big dish is easier than a few small dishes, depends on whether you are more adept at mechanics or electronics, and how often you need to reposition your dish. ------------------------------ Date: Tue, 19 Apr 1994 19:12:41 GMT From: ihnp4.ucsd.edu!usc!elroy.jpl.nasa.gov!ncar!csn!col.hp.com!srgenprp!alanb@network.ucsd.edu Subject: Slot antennas on cars? To: ham-ant@ucsd.edu Tom Bruhns (tomb@lsid.hp.com) wrote: : Has anyone out there experimented with slot antennas on cars? There are : several places you could make this work, but I was thinking of a slot : formed from wire (or copper tape) placed at the top inside of the rear : window. If anyone has experimented with this, I'd be interested in : the results: impressions about performance transmitting and receiving, : amount of RF in the passenger compartment, problems feeding the : antenna, ... It seems like the dimensions are right for this to work : as a "stealth" antenna on 2m and 440MHz, with vertical polarization. The front or rear window of a car makes a pretty decent slot antenna for the CB band (or 10 meters). It's shorter than resonant, but those who have tried it tell me that a small variable capacitor in series with the feed gives a low SWR. Connect the coax shield to the bottom of the window frame and connect the center conductor through the capacitor and a wire to the top of the frame at the middle. AL N1AL ------------------------------ End of Ham-Ant Digest V94 #113 ******************************