(Click on thumbnail to download full picture)
Caution: be advised that these tend to be large files. Importing them will consume considerable Web bandwidth and connect time.

Attn. Journalists and Photo Editors: please check our Fair Use Policy before reproducing any of these images. Thank you.

The photos below document the development by SETI League engineers of a 1420 MHz to 144 MHz microwave downconverter. More details on this and other equipment may be found in the SETI League Technical Manual.

The first step in developing a microwave downconverter is to produce a stable and pure local oscillator. This project employs an unmodified Down East Microwave WSS-1296 signal source kit, equipped with a 106.333 MHz crystal (multiplied x 12) to produce the required injection. Alternatively, a 116 MHz crystal oscillator, multiplied by 11, will provide the same injection frequency. SETI League photo

Spectral response of the Local Oscillator board. Output power is +4 dBm (about 3 mW). Spurious responses are down 30 dB. The 1276 MHz injection frequency converts the 1420 MHz hydrogen line for reception in a 144 MHz (2-meter band) ham receiver. SETI League photo

Next we need a mixer / amplifier module. The one for the prototype downconverter was produced by performing crude surgery on the same printed circuit board we used for the LO chain. Note that the LO board contains etched filters, MMIC amplifiers, and a crystal oscillator stage. All but the latter are useful for the front end. For the final kit version, a properly etched board is being developed. SETI League photo

The ends of all the filter poles for the front-end board have been shortened by 0.1 inches, to raise the resonant frequency from 1276 MHz to 1440 MHz. Connectors have been installed, and a surface-mount double-balanced mixer module affixed to the region of the board originally used for a diode frequency multiplier. SETI League photo

Closeup of the surface-mount mixer installed on the front-end board. Note the crudely cut 50 ohm microstripline running to the SMA connector at the right of the board. This connector is for applying local oscillator injection from the LO board shown above. SETI League photo

The completed front-end board contains a GaAs MMIC first stage, a three-pole etched bandpass filter, two silicon MMIC preamp stages, another etched filter, a mixer, and a single stage silicon MMIC IF amplifier. An SMA cable is needed to connect the LO chain to the front end board. SETI League photo

The completed SETI League hydrogen line (1420 MHz) to 2-meter (144 MHz) downconverter was first demonstrated at our Annual Meeting on 22 March 1997. At the Southeastern VHF Conference two weeks later, the prototype measured in at 1.85 dB noise figure and 49 dB conversion gain. This converter boasts over 50 dB image rejection and 30 dB spurious rejection. SETI League photo

The commercial version of the SETI League downconverter is sold by noted equipment supplier Down East Microwave, as their Model 1420-144RX for $195 (assembled and tested). Kits are also available, for $135 (parts and circuit board only) or $165 (parts, board, connectors and enclosure). A discount is offered to SETI League members in good standing. SETI League photo