Date: Fri, 17 Dec 93 04:30:10 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 V93 #145 To: Ham-Ant Ham-Ant Digest Fri, 17 Dec 93 Volume 93 : Issue 145 Today's Topics: Antenna Tuner Questions (2 msgs) Base Station Cellular Antennas Designing a Yagi. An Algorithm ? Mag North Vs True North More Antenna Tuner Questions 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: 16 Dec 93 17:18:30 GMT From: ogicse!hp-cv!hp-pcd!hpcvsnz!tomb@network.ucsd.edu Subject: Antenna Tuner Questions To: ham-ant@ucsd.edu Andrew Thomason (andrew@pmms.cam.ac.uk) wrote: : How do you obtain a variable : capacitor with neither side grounded? Do you use an ordinary : variable capacitor with its body (and shaft) physically isolated : from ground, or do there exist special types with neither side : of the capacitor connected to chassis? (It wasn't a stupid question, so I deleted that part ;-) You can put an insulated coupling on the shaft. I've also seen ones whose shaft has built-in insulation. Using this technique, it's even possible to build multi-section variables with moderately well isolated sections. I have one variable which must be nearly the ultimate in caps for an application like Alan described: it has two sets of circular plates. Each set is attached to a shaft at the edge of the stack. The shafts are parallel but separated by a bit less than the diameter of the plates. The thing is gear-driven, so the sets fully mesh at one extreme, and are completely separate at the other. The gears and the mounting plate for the shafts are insulated, and there is a wiping contact on each shaft. The result is a cap isolated pretty well from ground, balanced to ground, and capable of a very wide range from min to max (a bit over 100:1 in this particular case). 73, K7ITM ------------------------------ Date: 16 Dec 93 22:13:51 GMT From: ogicse!hp-cv!sdd.hp.com!col.hp.com!srgenprp!alanb@network.ucsd.edu Subject: Antenna Tuner Questions To: ham-ant@ucsd.edu Andrew Thomason (andrew@pmms.cam.ac.uk) wrote: : How do you obtain a variable : capacitor with neither side grounded? Do you use an ordinary : variable capacitor with its body (and shaft) physically isolated : from ground, or do there exist special types with neither side : of the capacitor connected to chassis? The most common way is to mount the capacitor on insulated posts and use an insulated coupling between the shaft and front-panel knob. AL N1AL ------------------------------ Date: Tue, 14 Dec 1993 23:28:40 GMT From: nwnexus!ole!ssc!tad@uunet.uu.net Subject: Base Station Cellular Antennas To: ham-ant@ucsd.edu Anyone have any recommendations for cellphone antennas when they are installed in a base station? I'm trying to figure out the best all around solution when we have a cellular transceiver (similar to the Tellular units) installed in heavily steel reinforced concrete buildings....specifically telephone company central office switches. (you may well wonder why, if we are INSIDE a local telephone exchange, we would need cellular service, but that is another rather complex story) In some cases this gear may be installed in the basement. I'm hoping that in some installations, a rubber duckie sticking out of the back of our box may be adequate for reaching the local cell site. In others, I am hoping that a 1/4 or 1/2 wave whip clamped to some overheard cable ducts may to do the trick. In others we may have to actually go outside the building, which I want to avoid because of telco concerns about lightning in these installations. Anyone have any knowledge of similar installations, like maybe those alarm systems that use cellular? Any antenna recommendations for easy installations? If you email, send to 3991080@mcimail.com -- tad@ssc.com (if it bounces, use 3288544@mcimail.com)| [put "attn Box #215" Tad Cook | Packet Amateur Radio: | Home Phone: | on fax or cover pg!] Seattle, WA | KT7H @ N7DUO.WA.USA.NA | 206-527-4089 | FAX: 206-525-1791 ------------------------------ Date: 16 Dec 93 22:11:57 GMT From: ogicse!hp-cv!sdd.hp.com!col.hp.com!srgenprp!alanb@network.ucsd.edu Subject: Designing a Yagi. An Algorithm ? To: ham-ant@ucsd.edu elendir@enst.fr wrote: : I know some now PD programs help you designing Yagi antennae (e.g. the : excellent Yagimax). Since I have no PC at home, I was wondering if anybody : were aware of the algorithm used by those utilities, in order to write a : version for my own computer. : Were can I find such info ? The book "Yagi Antennas" by Lawson gives the required information to get you started, assuming you are very math- and computer-literate. I believe you can get it from the ARRL. AL N1AL ------------------------------ Date: Thu, 9 Dec 1993 13:02:59 GMT From: netcomsv!netcom.com!greg@decwrl.dec.com Subject: Mag North Vs True North To: ham-ant@ucsd.edu In article <171480001@hpcuhe.cup.hp.com> donh@hpcuhe.cup.hp.com (Don Hay) writes: > Greetings fellow Hams....... > >While checking a beam heading the other night, the following question >came to mind. In San Jose, where I live, Magnetic North is 16 degrees >east of true north. If my beam heading is 'true north', will the RF >be squed by the fact that magnetic north is to the east? In other words, >does the magnetic properties of the earth cause signal squing problems? >Don't think this is really a problem as the beam pattern is quite spread >at a distance anyway. I just found this to be an interesting thought! > >Anyone care to comment? And of course the related, but equally puzzling question; if everyone comes home at night and turns on their television at prime-time, does the signal get weaker in fringe areas because of the number of receivers which are now consuming more microvolts of signal close in? Greg ------------------------------ Date: 16 Dec 93 23:03:27 GMT From: ogicse!uwm.edu!cs.utexas.edu!howland.reston.ans.net!spool.mu.edu!news.nd.edu!mac05@network.ucsd.edu Subject: More Antenna Tuner Questions To: ham-ant@ucsd.edu I've enjoyed the recent postings on antenna tuner designs, and wonder whether anyone could indicate how they apply to tuners available commercially? Are most of these designs not pi tuners? Any significant differences between brands? Does investing in one of the more expensive models really pay off? I've been thinking about trying out out the MFJ differential T tuner. ------------------------------ End of Ham-Ant Digest V93 #145 ****************************** ******************************