Constructing 8 dipole doppler array
2016.03.26.A
N0ZYC


Last year I decided to improve my array to 8 elements.  This wasn't intended for handheld or even portable use.  It was designed to give improved precision at a base installation.

I chose to continue with the "18" on a side" dimensions from the previous design, but to simply double the number of dipoles used.  This would require building a new array, a new combiner, and possibly modifying my control box as well.

Using PVC pipe again, I toyed around with differnet ideas but it quickly became apparent that I couldn't star 8 arms out from the middle easily, so I decided to go with 4 arms out, and split them.  This made measuring pipe lengths quite a bit more complicated.  Although scan radius wasn't too critical, I did need to maintain as accurate of element spacing as possible.  I also saw this was going to be a much heavier array, and sought to keep weight down where possible.

To limit weight, I decicded to go with 3/4" PVC for strength in the middle, but change to 1/2" as I got out to the dipoles.  This added only a little more complexity to the measurements.  After the math was done, I determined that the four 3/4" main arms needed to be 270mm long, and the 1/2" dipole arms needed to be 84mm long, factoring in the 3/4 to 1/2" reducers.  I was pleased with the results, where distance between dpioles was consistently 25cm, and radius from center was 32cm. (32cm was the same as my four element array)

I haven't gotten any further with this yet, I'm waiting on design of a new doppler controller.  Having so many antennas and only one (very ramshackle) controller is making me a bit nervous as it's a giant single-point-of-failure that needs to be eliminated.