1420-MHz FEED HORNS
1420-MHz Short Helix Dish Feed
NOTE-The previous text was incorrect. Modified 4/11/2009
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 right-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 left-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.
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