Xref: utzoo rec.radio.shortwave:4678 rec.ham-radio:29034 sci.electronics:16580 Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!mips!bridge2!api!gpz From: gpz@ESD.3Com.COM (G. Paul Ziemba) Newsgroups: rec.radio.shortwave,rec.ham-radio,sci.electronics Subject: Re: Ground Plane for my CB antenna Message-ID: Date: 31 Dec 90 07:45:19 GMT References: Sender: news@bridge2.ESD.3Com.COM Followup-To: rec.radio.shortwave Lines: 72 steven@ozonebbs.UUCP (Steven Rubin) writes: +I want to put the antenna on my roof, but I am having trouble +finding a good ground plane. The manager at Radio Shack suggest getting a +peice of sheetmetal for a ground plane. How big should I make the sheet +metal? 1. Yet Another Reason to Avoid Radio Shaft (YARTARS) This radio shlak person, like most, is talking through his hat. I can see the headlines now..._18-foot flying saucer lands on house_. I can not imagine buying, let alone installing, such a collossal piece of metal. Where does radio slock find these incredibly dense people? 2. a. The bad news: the ground plane should be at least a quarter-wavelength in radius, which, for 27 MHz, is about...(slip, slip, slip)...107 inches. b. The Good news: it doesn't have to be solid; in fact, you can get away with three or four pieces of wire instead. Side view: | | (center conductor of coax connects to this) | | ------+------ ground plane (braid of coax connects to this) Top view: | | | -----+----- | | | Sometimes people bend the ground plane radials downward, which raises the feedpoint impedance of the antenna from ~30 ohms to something closer to 50 ohms. This is desirable because the most if not all CBs are designed to operate with a 50 ohm antenna impedance. Note that the radials do not have to be stiff...they can be pieces of wire tied down at both ends. They should be connected electrically in any case. Base station antennas of this sort usually have a full-length quarter-wave vertical element, as opposed to a physically shorter one with a coil. What type of antenna are you currently using? I'm guessing it's a mobile antenna with a loading coil of some sort. If that is the case, you might be better off just buying a regular base station antenna as long as you are going to this much trouble, since the full-length antenna will perform somewhat better (how much better? well, maybe 36.438764356 percent). Wow, it's a good thing I don't read rec.ham-radio, since there will most assuredly be 6.02E23 other replies all saying this same thing, or pointing out that a full-length antenna will really perform 36.438764357% better, or asking if the resulting antenna would be FCC type-accepted or would it be against the rules part 95.7863(a) paragraph 3 section t etc. etc. etc. :-) Good luck! ~!paul Discalimer: I am not a CBer. -- Paul Ziemba api!gpz gpz@ESD.3com.com 408.764.5390 You don't exist. Go away.