1420-MHz Short Helix Dish Feed

   I have had a 3-1/4 turn home-made helical beam mounted to the side of my 10-GHz waveguide
   feed on my 2.4 meter (8-foot) dish for a few year.  The dish has been fixed at 36-degrees
   elevation and pointed south for radio astronomy and SETI observations in the meridian scan
   or "drift scan" mode.

   The helix is wrapped for left-hand circular polarization using no. 12 solid copper wire
   around a plywood form.  Polarization is reversed when it reflects from the dish surface
   resulting in right-hand CP.  The helix is impedance matched to the 50-ohm coax connector
   via a short brass stripline close-spaced to the 3-inch square aluminum reflector.  The
   LNA is made for Radio Astronomy Supply by WD5AGO and is a two-stage GasFet preamp with
   0.30 dB NF and 31 dB gain over the 1296-1420 MHz spectrum.

   Here are a couple photos of this feed:




   






   I have replacied the helix feed with a square waveguide feedhorn.  Look on my Septum webpage.