[GreenKeys] OT. Antenna materials

Sun Dec 1 08:15:38 EST 2013

At 2 meters skin effect limits the signal (tx or rx) to about .00025 
inch penetration in the conductor. Anything thicker is structural. 
Copper foil on a balsa dowel or a thin fiberglass tube should work 
fine as long as overlap points were connected as you mentioned with 
solder tacks.

Ken S

   At 11:59 PM 11/30/2013, you wrote:
>Hey guys:
>
>Well, when I mentioned wrapping a dowel with copper tape, I didn't 
>mean some helical thing -- I have a big roll of adhesive copper tape 
>and was thinking of a linear strip of tape along the length of the 
>dowel, that completely wrapped the dowel, with some solder tacks 
>every few inches where it overlaps, forming a pseudo copper 
>tube.  Is that not a good tubular conductor for a dipole if wrapped 
>around a 3/16" wood dowel?  The dowel will not get wet, btw, as we 
>will only launch on a clear day.
>
>Brass hobby tubing is also a good suggestion, though the dowel will 
>be there and it seems reasonable to exploit it.
>
>My original plan was to just take some 24-ga or whatever copper 
>enameled magnet wire and epoxy it it along the wood dowel 
>structure.  But it sounds like such thin conductors make the 
>bandwidth narrow, and would make tuning the dipole length all that 
>more critical.
>
>Regarding tuning:  I can likely measure the antenna impedance with 
>my HP TDR that goes to 20 GHz, but how can I measure the antenna's 
>resonant freq (at x-distance above ground)?  Do I need to buy an swr 
>meter or antenna analyzer, or is there a way to do this with 
>conventional test equipment that I already have (scope, spectrum 
>analyzer...)?  Or is it not that big a deal?  Just cut it to x and 
>call it good?  Am I over-thinking this?  I often do, but rather that 
>than the opposite extreme.
>
>gil
>
>
>gil smith, AF7EZ
>greenkeys moderator
><mailto:gil at baudot.net>gil at baudot.net
>
>
>-------- Original Message --------
>Subject: Re: [GreenKeys] OT. Antenna materials
>From: Jeffrey D Angus <<mailto:jdangus at att.net>jdangus at att.net>
>Date: Sat, November 30, 2013 10:02 pm
>To: <mailto:greenkeys at mailman.qth.net>greenkeys at mailman.qth.net
>
>On 11/30/2013 10:15 PM, <mailto:WA5CAB at cs.com>WA5CAB at cs.com wrote:
>>I was just about to write the same thing WRT the adhesive tape.
>>If you wrap it around and around the dowel, you'd have to have a
>>bit of overlap and even then you are at the mercy of how good a
>>conductor the adhesive is (probably not good at all).  Using thin
>>wall brass tubing would be a better idea, as Jeff suggests.
>Here's an excellent source of it.
><<http://www.ebay.com/itm/331057652528>http://www.ebay.com/itm/331057652528>
>5 pieces of 1/8" diameter x 36" long brass tubing for under $17.
>
>This is the classic "cheap and dirty" 1/4-wave antenna.
><<http://farm4.static.flickr.com/3604/3380705199_e6f4b71366.jpg>http://farm4.static.flickr.com/3604/3380705199_e6f4b71366.jpg>
>
>The magic number is 19". You can get better results by fine tuning the
>lengths, but just "chop it at 19 inches" works well enough.
>
>You can make something similar with the brass tubing . As long as
>the balloon is airborne, It will transmit quite well hanging upside
>down underneath it.
>
>Even stabbed into the ground a bit, after landing, you should be
>able to hear a reasonable signal if you're close to it. And if it gets
>stuck in a tree, all the better to locate it.
>
>While you're at it, look into "fox hunting." The techniques for
>locating "hidden" transmitters for sport or locating jammers.
>
>Jeff-1.0
>wa6fwi
>
>
>
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