Adding polarisation change to the bay
October 2011
Note: I have abandoned this concept in 2012 for no particular reason! I may resurrect it; I may not.
After using the antennas for ten months for 6M EME activities I have found, like all others, that polarisation change in the form of spatial polarisation and/or Faraday can have a terrific impact on the ability to decode JT65A signals. I have found that many a time I have experienced long polarisation 'lock-outs' before I could see a signal. A good overview of these effects and their impact can been obtained on G3SEK's web site and also N1BUG's web site.
After using the antennas for ten months for 6M EME activities I have found, like all others, that
polarisation change in the form of spatial polarisation and/or Faraday can have a terrific impact on the ability to decode JT65A signals. I have found that many a time I have experienced long
polarisation 'lock-outs' before I could see a signal. A good overview of these effects and their impact can been obtained on
G3SEK's web site.
I therefore thought it might be worthwhile trying to add the ability to change polarisation to the bayed array.
How successful this will be mechanically or from the ability to better decode signals from the moon remains to be seen!
There are two ways of achieving this with Yagi antennas: (A) Add a second set of elements at rights angles to horizontal antenna and add electrical switching
between the two. This has two disadvantages (1) the array will be very heavy! (2) I could only switch between horizontal and vertical polarisation and nothing in between.
(B) Mechanically rotate the antenna. This approach would weigh less and allow me to experiment with intermediate angles other than 0 and 90 degrees.
After a lot of consideration I chose option (B).
The drawings for the mechanics are as follows.
The hinge assembly
The elevation linear actuator arrangement
I have used two piece of 1 29/32" and 1 1/2" 10 gauge aluminium tube as the basis of the hinge obtained from Aluminium Warehouse.
The 'hinges'
These will be attached to the 8mm base plates.
The 8mm aluminium mounting plates
This is the complete welded hinge on which I will mount the antenna.
The welded 'toilet roll holder' hinge
The hinge is now temporally bolted to the base plate:
The welded 'toilet roll holder' hinge screwed on the mounting plate