Re: [amsat-bb] Circulair patch behaves linear

["Frederick M. Spinner" <fspinner@xxxxxxxxxxx>]

William-

Do yourself a favor, and build the G3RUH style patch at W0LMD's site.  Add 
the second tuning screw as I stated in a previous e-mail.  Make the CP 
tuning screw a #8 or #10 instead of the #6 on his site.

So far it is the ONLY patch I have made that has tested circular.  Yes this 
is with tuning with the screws but I venture to guess you could make those 
adjustments while listening to the beacon.

By comparison to the other patches I've built, its more mechanically stable, 
only a little harder to construct (cutting the discs requires access to a 
shear or precise scroll saw), but it is SOO easy to adjust conpared to the 
Nearly Square and K3TZ style antennas.

There is a point where the "CP" tuning screw on that patch will magically 
make the patch LHCP.  Trust me, I've seen it on a Network Analyzer.

Fred W0FMS


>From: "William Leijenaar" <pe1rah@hotmail.com>
>To: amsat-bb@AMSAT.Org
>Subject: [amsat-bb] Circulair patch behaves linear
>Date: Sat, 21 Jun 2003 21:31:01 +0200
>
>Hi AMSATs,
>
>Some time ago I posted some message where I discribed my discovery that I 
>using a RHCP in front of my dish for long times without any problems 
>recieving AO40. This made me suggest that my patch was not that circulair 
>as many amateurs believe it is. Later when I made a LHCP version, that is 
>even more accurate than the previous RHCP one I could not hear very much 
>difference.
>
>On that message I recieved some emails from other amateurs who also tested 
>patches with results that showed that the so called circulair patch in not 
>realy circulair. With this information I wanted to know if this circularity 
>belongs more to the fairy-tale world or more to the reality.
>
>Today it was a very nice and sunny day, so I decided to make some test 
>setup and test the patch.
>I made some 13cm linear metal can antenna out of an fruit can :o) which has 
>the right diameter...
>At some 150m distance in the garden I put the metal can with a 13cm test 
>signal on it and see what my patch was recieving.
>
>While I was rotating the (so called circulair) patch I measured a 9dB 
>difference !!!!
>The best signal I got when the feed-point of the patch was on top, with a 
>vertical polarisation recieved.
>Below the situation in a picture. (The picture shows the radiating plate, 
>the reflector is not shown)
>
>  ***********
>  *                 \
>  *        +        *     + = 50E feed point (BNC connector)
>  *                  *
>  *                  *     <-- Along this x-axis the signal strenght is 9dB 
>lower than
>  *                  *          along the y-axis.
>   \                 *
>    ***********
>
>        ^-- Along this y-axis the polarisation is the best (9dB better than 
>along x-axis!!!)
>
>I don't say that a patch can not be made circulair, but after checking all 
>the sizes that are well within
>1mm I am suprised to find even a 9dB difference with these minor size 
>differences !!!! The sizes I have taken out of the publication in AMSAT-DL 
>magazine MAI 2003. The patch plate is from coper with a aluminium reflector 
>plate and 100% air spacing between them. (There are no distance keepers 
>that could cause any problems)
>
>In my opinion the so called "simple to make circulair patch", doesn't 
>dignify its glory.
>The combination of "simple to make" and "circulair" belong for me to the 
>fairy-tales.
>I believe that patches can be made near to 100% circulair, but this is only 
>for those who can measure it and have the equipment to make all sizes very 
>accurate.
>
>For all those patch freaks, don't worry... even with this 9dB difference 
>you have 5% more signal reception than with a linear patch :o)
>
>We just go on and have fun in satellite radio,
>73 de PE1RAH, William
>---
>
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