...septum feedhorn

(after the OK1DFC design...ref: www.OK1DFC.com)

 

...receive port (SMA connector) side of the 1296 MHz septum-polarized feedhorn (April 25, 2005).

...transmit (type N connector) port side of the septum-polarized feedhorn (April 25, 2005).

...inside view showing the (stepped) septum plate that creates circular-polarized radiation from the transmit monopole and that passes opposite-sense circular-polarized waves to the receive monopole. The receive and transmit monopoles are visible in this photo (April 25, 2005).

...rear view of the 1296 MHz septum-polarized feed horn. Tx and Rx tuning disks are not yet installed on the back plate of the horn (April 25, 2005).

...installing the assembled septum-polarized feedhorn (April 25, 2005).

...close up view of the receive SMA connector, T/R relay, and preamp. Note that there are no adapters of any kind in the connections AHEAD of the preamp! Any such adapters increase the noise figure of the receive system dramatically. Of course, adapters can be used AFTER the preamp with negligile detrimental effect (April 28, 2005).

...back plate removed showing the Tx and Rx monopoles. Monopoles are made of silver-copper-alloy rod 0.1" diameter (silver-solder brazing rod). Each monopole is 40mm long. The stepped septum plate is also clearly visible in this photo (April 28, 2005).

...back plate showing the Tx and Rx tuning disks. The tuning disks were fashioned from two 3-inch-long 1/4"-20 brass screws. The screwdriver slot of each screw was ground flat to form a capacitive disk that faces the monopole (April 28, 2005).

...completed back plate, installed on the horn (April 28, 2005).

...test set up used to resonate the Rx monople at 1296 MHz while the horn is mounted on the dish. The IC-910 (w/UX-910 1296 MHz module) transceiver provided a low power test signal into the Rx SMA port. The Rx tuning screw was adjusted to achieve minimum reflected power on the Diawa 1296 MHz crossed-needle SWR/Power meter. Both Tx and Rx tuned easily to 1296MHz using the tuning screws. Transmit VSWR is no greater than 1.02:1 measured from the hamshack (April 28, 2005).

PERFORMANCE RESULTS: Using the septum-polarized feedhorn and 400 watts of output power in the shack and 200 watts at the feedhorn, I receive my own echoes from the moon at 6 to 7 S-units (approx 20 dB) above background noise. Moon noise measures 0.6 dB above background and sun noise (solar flux 79.3...low SFU on this day!) is 19.0 dB (June 22, 2005).


UPDATE (April 2007): For EME QSOs I currently use a VE4MA-style feedhorn as shown in the photograph on the "Home Page" and "Using Sun Noise" page. For radio astronomy observations the VE4MA horn is replaced by a linear-polarization feed horn (round waveguide, no phasing screws or septum plate, and a circular scalar ring). The linear polarization feed is shown installed on the dish in the photograph on the "Radio Astronomy/Radio TelescopeAntenna" page. The previously used (but currently not used) square septum feed is shown installed on the dish in the photograph on the "EME Contacts" page.