Hi Henk, PA3GUO
Since the physical distance between elements of your 70 cm crossed yagi is 1/4 wave over the boom I suggest you to read my article: "Switching four Polarizations on a 70 cm Crossed Yagi" published by the AMSAT-Journal
Part-1 ( the theory ) issue of March/April 2007 Part-2 (construction) issue of May/June 2007
If you need the above articles I can send to you a pdf file of it.
73" de
i8CVS Domenico
----- Original Message ----- From: "Henk, PA3GUO" [email protected] To: [email protected]; <""@iae.nl> Cc: [email protected] Sent: Saturday, September 20, 2008 5:03 PM Subject: [amsat-bb] Re: More: circular polarization (1/4wave physicaldistance)
Maybe my question becomes clearer with thse pictures (taken today)
this morning, the original set-up, on the roof http://www.pa3guo.com/416_original.jpg
this afternoon, stripped, waiting for advice from the amsat-bb :-) http://www.pa3guo.com/416_stripped.jpg
Henk
So !
As the discussion is ongoing anyway:
This is how I have done it for 2 meters:
- 2 x 6 elements (phyically same position, no 1/4wave distance http://www.pa3guo.com/dk7zb.html
- switch box for H/V/LHCP/RHCP in the shack (2 long cables needed) http://www.pa3guo.com/polarizer.html
But now 70cm ! My 13 year old Cushcraft had always fixed circular polarization.
- 435.300 (AO51) had never any fading and was strong
- 435.150 (AO51) I could barely hear (proofs the >20 db separation)
Now: as AO51 will be in an mode that I want to use in the coming days, with the 435.150 downlink, I needed to change the polarization.
Initially I wanted to have a temporal situation (swapping the coax on the front dipol), but the screws needed replacement anyway, so I
decided to take the whole antenna down.
The 2x8 elements beam has the 2 antennas mounted 1/4 wave distance
spaced on the boom (the physical method).
Now, I want to be able to switch between LHCP and RHCP. Not fixed.
A good website I found is: http://sv1bsx.50webs.com/antenna-pol/polarization.html
At the bottom the physical method for CP is described. Almost what I needed, now I need to be able to switch on top of that.
I would assume that this should still be possible :-) My preference would be only LHCP and RCHP, no need for Hor or Ver.
Prefer to have eg the coaxes of the 2 beams to a small relay box on the back of the beam and then with a relais create the RHCP vs LCHP.... but I lack the schematic for that :-)
... can someone point me to a URL that has the solution described ?
OR: would it be simply this:
- take the front dipol
- swap conductor/shielding to create LHCP or RCHP AT the solder points
?
(is this how WIMO is able to get it all in their small boxes)
Well, I have 2 days before AO51 is in the mode I requested, I really need to get the antenna in place :-)
Thanks !
Henk, PA3GUO http://www.pa3guo.com
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