Date: Thu, 17 Feb 94 04:30:39 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 #36 To: Ham-Ant Ham-Ant Digest Thu, 17 Feb 94 Volume 94 : Issue 36 Today's Topics: 6 Meter Big Wheel Ant? Antenna size vs frequecy? Bug Fix for MINNINEC from Feb. 94 QST Difference between Cushcraft A147-20T & A144-20T Increasing antenna sensativity? mininec3 Radiation efficiency questions ... rotator ??? (2 msgs) Sterba Curtain Torroid Cores 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: 14 Feb 1994 16:47:49 GMT From: swrinde!cs.utexas.edu!sdd.hp.com!col.hp.com!srgenprp!news.dtc.hp.com!hpscit.sc.hp.com!rkarlqu@network.ucsd.edu Subject: 6 Meter Big Wheel Ant? To: ham-ant@ucsd.edu In article , Henry B. Smith wrote: >Has anybody ever seen the plans for a 6 Meter Big Wheel Antenna? > >If so, please pass along the reference. > >Thanks, > >Smitty, NA5K The Big Wheel was described in the ARRL VHF Manual a number of years ago. I have an old copy (circa 1965) that has this antenna and also the old halo mobile antennas in it. They quit publishing omni-directional horizontally polarized antennas when hams switched from AM-horizontal-simplex-mobile to FM-vertical-repeater-mobile in the early 70's. It's basically 3 loops a full wavelength long built like a 3 leaf clover. Much better than a halo, according to the book. I think you drive the loops in parallel, but don't quote me, I'm working from memory here. Rick Karlquist N6RK rkarlqu@scd.hp.com ------------------------------ Date: Mon, 14 Feb 1994 15:25:04 GMT From: swrinde!cs.utexas.edu!howland.reston.ans.net!europa.eng.gtefsd.com!emory!news-feed-1.peachnet.edu!news-feed-2.peachnet.edu!concert!inxs.concert.net!taco!dmndcentris.mte.ncsu.edu!sdtrent@network. Subject: Antenna size vs frequecy? To: ham-ant@ucsd.edu Hello, I read years ago that the optimum length of an antenna is 1/2 wavelength of the frequency being received, this article was talking about commercial FM. Is this true (no equations needed)? Also, would this apply to a dish antenna? What size microwave (900 MHz) should be used? Thanks for your help, -shane ------------------------------ Date: 16 Feb 1994 17:18:01 GMT From: koriel!male.EBay.Sun.COM!uranium!raymonda@ames.arpa Subject: Bug Fix for MINNINEC from Feb. 94 QST To: ham-ant@ucsd.edu The following letter was published in the Technical Correspondence column of the February 1994 issue of QST magazine (page 76). It addresses a couple of bugs in MINNINEC identified by Brian Beezley K6STI (Author of MN, YO, and AO). Ray Anderson WB6TPU raymonda@uranium.ebay.sun.com ---------------start of included text ----------------- MININEC BUGS: K6STI PLAYS EXTERMINATOR I recently discovered two bugs in the MININEC antenna-analysis program. The most serious bug yields incorrect patterns for antenna models with grounded wires. The error overstates gain at low elevation angles by as much as several decibels. The problem occurs only for models with wires connected to imperfect ground. The bug does not affect models using perfect ground or models with ungrounded wires. The error decreases as you add segments to grounded wires. Therefore, if you habi- tually test algorithm convergence by creasing segmentation density until results no longer change significantly, the prob- lem won't affect your results. However, I doubt that most users check convergence for simple models. Since the bug affects models regardless of complexity, I believe that the error often goes unnoticed. You can check any MININEC-based program for this bug by modeling a quar- ter-wave monopole over imperfect ground and observing the response at zero degrees elevation. There should be no response at the horizon because direct radiation is can- celed by that reflected from ground. Un- corrected MININEC will show a significant response unless you use an unusually high number of segments. In contrast, the cor- rected algorithm has no response regard- less of segmentation. If you compile your own MINNINEC code, you can fix this bug by deleting lines 716, 717 and 733. After the change, lines 741 through 744 are no longer used and can be deleted as well. The original code erro- neously uses perfect ground when calculat- ing the field from pulses connected to imperfect ground. Perfect ground rein- forces rather than cancels radiation near the horizon, so the grounded contribution cor- rupts the field summation calculated cor- rectly for other pulses. The second MININEC bug occurs only for sloping, grounded wires in the X=-Y plane. Since this geometry isn't common, you may never encounter the problem. The bug causes completely erroneous results that can be corrected only by moving the wires out of the plane. The error involves overzealous removal of redundant calcula- tions. You can fix this bug by correcting two lines as follows: 239 IF CA(I1)=O AND CB(I1)=O THEN 241 242 IF CA(J1)=O AND CB(J1)=O THEN 244 --Brian Beezley, K6STI, 507 1/2 Taylor St. Vista, CA 92084 ---------------------end of included text------------------- ------------------------------ Date: Mon, 14 Feb 1994 19:55:50 GMT From: ucsnews!newshub.sdsu.edu!usc!yeshua.marcam.com!zip.eecs.umich.edu!umn.edu!uum1!ncrtimes!tblake.stpaul.ncr.com!tony.blake@network.ucsd.edu Subject: Difference between Cushcraft A147-20T & A144-20T To: ham-ant@ucsd.edu Hi Gang, I am making some final decisions on what VHF equipment to purchase. My long range plan is to work the satellites, but for now be content with terrestrial work. For now, I want to run the Cushcraft A147-20T. However, while looking over Cushcraft's AOP-1 OSCAR system, I noticed that one of the 2m antennas is their A144-20T. This antenna appears to be identical to the A147-20T. Does anyone know what the difference is between these two antennas? Will I be able to use the A147-20T for OSCAR work in the future? Thanks, ======================================================================= Tony Blake DoD#9045 AT&T Global Information Solutions tony.blake@ccmsmtp.stpaul.ncr.com Network Products Division (612) 638-7259 voice 2700 Snelling Avenue North (612) 638-8173 fax St Paul, MN 55113-1784 Disclaimer: The smelling pistakes are all my own. ======================================================================= ------------------------------ Date: 15 Feb 1994 07:50:58 GMT From: ucsnews!newshub.sdsu.edu!usc!howland.reston.ans.net!europa.eng.gtefsd.com!mozart.amil.jhu.edu!blaze.cs.jhu.edu!vincie@network.ucsd.edu Subject: Increasing antenna sensativity? To: ham-ant@ucsd.edu I don't know if this is the most appropriate newsgroup. (It's the closest one except for sci.electronics.) I'm mainly interesting in received AM broadcasts. (I haven't had a chance to start my interest in amateur radio.) I need to construct a better antenna. Most receivers have that cheap multi-loop antenna. Im' just curious if that is the best design for AM reception? Would multi-segmented wires be better? How about more loops and larger loops? Thanks... Michael ------------------------------ Date: Wed, 16 Feb 94 06:52:21 GMT From: amd!netcomsv!skyld!jangus@decwrl.dec.com Subject: mininec3 To: ham-ant@ucsd.edu I found it! And it works. And yes, cryptic is one way to describe it. It is on ftp.funet.fi in the directory /pub/dx/software/msdos/antenna Heh, share and enjoy! Amateur: WA6FWI@WA6FWI.#SOCA.CA.USA.NA | "You have a flair for adding Internet: jangus@skyld.grendel.com | a fanciful dimension to any US Mail: PO Box 4425 Carson, CA 90749 | story." Phone: 1 (310) 324-6080 | Peking Noodle Co. ------------------------------ Date: Wed, 16 Feb 1994 13:56:24 GMT From: agate!howland.reston.ans.net!gatech!wa4mei.ping.com!ke4zv!gary@network.ucsd.edu Subject: Radiation efficiency questions ... To: ham-ant@ucsd.edu In article ae517@FreeNet.Carleton.CA (Russ Renaud) writes: >In a previous article, tavernin@sun1.interlan.com (Victor Tavernini) says: >>I have a couple of questions about radiation efficiency ... >>1. What is the radiation efficiency (compared to a 10 meter dipole) of >>a 15 meter dipole used at 10 meters with an antenna tuner!? >>2. What is the radiation efficiency (compared to a 40 meter dipole) of >>a 15 meter dipole used at 40 meters with an antenna tuner!? > >Radiation efficiency has very little to do with resonance. True. A non-resonant antenna is just more difficult to drive efficently. >In both cases, as long as associated losses remain the same, the radiation >efficiency should be equal. Not true I think. To generate the same field, the shorter antenna will require a higher potential across it, and higher current flowing through it. So the shorter antenna will have increased I^2R losses given the same wire size. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | uunet!rsiatl!ke4zv!gary 534 Shannon Way | Guaranteed! | emory!kd4nc!ke4zv!gary Lawrenceville, GA 30244 | | ------------------------------ Date: 15 Feb 94 15:28:12 GMT From: yuma!galen@purdue.edu Subject: rotator ??? To: ham-ant@ucsd.edu In article Chris Beasley writes: >Hey folks, looks like it's time to consult the net.wisdom on this one. >I have an old (circa 1960) Channelmaster antenna rotator and a page >of documetation that includes the rotator and the controller. From >the schematic, it appears that the rotator and controller are just a >pair of 90degree windings at about 8 ohms each that are connected >together to form a synchro pair? Much deleted. >Thanx in advance and 73! >Chris >N3PDG I think what you have are called SELSYNS. I have a c1951 Air Force Radar manual that describes them in some detail. Manual states they are also called SYNCHRO, AUTOSYN, and SYNCHROTIE. Try looking in some OLD radar/radio books. My book is titled 'Radar Circuit Analysis, AF Manual 52-8'. Galen, KF0YJ ------------------------------ Date: Mon, 14 Feb 1994 16:28:32 -0500 From: elroy.jpl.nasa.gov!swrinde!cs.utexas.edu!math.ohio-state.edu!cis.ohio-state.edu!news.sei.cmu.edu!bb3.andrew.cmu.edu!andrew.cmu.edu!cb1p+@ames.arpa Subject: rotator ??? To: ham-ant@ucsd.edu Hey folks, looks like it's time to consult the net.wisdom on this one. I have an old (circa 1960) Channelmaster antenna rotator and a page of documetation that includes the rotator and the controller. From the schematic, it appears that the rotator and controller are just a pair of 90degree windings at about 8 ohms each that are connected together to form a synchro pair? The only difference between the rotator and the controller is that there is another xformer in the controller hooked up to line AC on one side and with two secondaries hooked up to the "control windings?" in the controller. I guess I could try to imitate some lame ascii graphics or something :-/ Rotator Controller Rotator --------------------------------------------- | | | < < | > > | < < | | | | --/V\/V/\/V\-C-/V\/V\/V\-- ----------/V\/V/\/V\-C-/V\/V\/V\-- | | > > < < > > | -------------| Whew, that's a bitch! I am not gonna get the whole schem. this way. how about if I just elaborate verbally.... The rotator on the right appears to have four windings connected into two that are not connected in the center, thus forming two 90 degree windings. The two ends are commoned to produce the line I call "common" going back to the controller. The other two lines going back to the controller are the two winding power lines. There is something in the controller that is the same that I am calling the control transformer for lack of a better term. There is also a transformer hooked up to 120VAC with two secondaries, a switch (probably for direction sense) and a capacitor. If this is all still too confusing I can try to enter more of the schems. What I am wonderign is, how to control this rotator. Eventually I would like to hook up to my computer but for now I would be happy to have a box with compass points and a dial on it. I have one of those actually but it seems to be the wrong kind. It has four wires to connect to for one thing and has a solenoid that I think is supposed to move a compass needle when pulses come back from the rotator. It doesn't work with my rotator any way I have tried to hook it up. Can anybody help me with this? Tell me what kind of rotator I have and what kind of controller I need? Where to get one? Any additional info will be appreciated! Thanx in advance and 73! Chris N3PDG ------------------------------ Date: Mon, 14 Feb 94 19:43:37 GMT From: news.crd.ge.com!sarah!eve!gl8574@cs.rochester.edu Subject: Sterba Curtain To: ham-ant@ucsd.edu While this does not answer the question in particular, I have one of my own regarding this beast. Has anybody out there attempted to build one of these from a material other than wire (copper pipe, for example)? I had been toying with the idea of building one from 1/2 inch copper pipe. Naturally, you wouldn't want to try this on anything much below 2m without some serious structural support.... Now a possible anser to the question-- is it possible to get some heavy steel cable, like one might use for a light tow cable, in a copperweld? The only problem I could see with using a design like that would be on the two inner verticals, where the thing might short out.... Just an idea. -- -- gl8574@cs.albany.edu "Not a jock or a geek, not a nerd or a greek, not quite normal, not really a friek, just me.... Deal with it!" -Critter ------------------------------ Date: Wed, 16 Feb 1994 14:52:00 GMT From: utcsri!newsflash.concordia.ca!pavo.concordia.ca!md_hill@uunet.uu.net Subject: Torroid Cores To: ham-ant@ucsd.edu I was digging through my junk (read "treasure trove of electronic stuff") the other day when I came across a bag full of torroid cores. I often read articles requiring a certain company's core #123XYZ. Question is: how do you know if the core that you happen to have on hand is usable ?. Is there a catalog somewhere that cross-references various manufactures numbers ?. Example: I have two cores in front of me; one is 1 9/16" (40mm) O.D. and 15/16" (24 mm) I.D. and bears the number A-254168-2. I think this is an Amidon core. The other is 1 7/16" (36mm) O.D. and 7/8" (23mm) I.D. with the number K300501 (B6A). Do these numbers mean anything to anyone ? Thanks -Mark Hillier Internet: MD_HILL@pavo.concordia.ca Amateur: VE2HVW PACKET: VE2HVW@VE2FKB " I hear, I forget. I see, I remember. I do, I understand" -Mark Message-ID: <16FEB199409520503@pavo.concordia.ca> Organization: Concordia University News-Software: VAX/VMS VNEWS 1.41 ------------------------------ End of Ham-Ant Digest V94 #36 ******************************