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In 2001, the Arecibo Radio Oservatory in Puerto Rico, home to the world's largest radio telescope, hosted SETI observations of the California-based SETI Insitute's Project Phoneix targeted search. The SETI League's Lunar reflective microwave beacon for radio astronomy and SETI was initially developed in support of that effort. David Parker / Science Photo Library

For years Project Phoneix scientists used the microwave beacon transmitter aboard the Pioneer 10 spacecraft as a calibrator, to verify the proper operation of their equipment. At a distance of 11.5 billion km from Earth, that signal was no longer accessible to Arecibo in March of 2000. Work on The SETI League's moonbounce beacon was begun at that time, to provide an alternative calibration source for radio telescopes worldwide. NASA/JPL image

Block diagram of The SETI League moonbounce beacon. The individual stages are described below. SETI League image

The SETI League moonbounce beacon antenna system. The station initially used four Olde Antenna Lab 15-turn helices wound for right-hand circular polarization (for transmit), and four more wound LHCP (to receive echoes off the Moon). The antennas are fully adjustable in azimuth and elevation using a Yaesu G5600B rotor system. Note that the helices are counterweighted to minimize torque on the elevation rotor. N6TX photo

The moonbounce beacon operates fully under computer control, and can be remotely commanded via the internet. These computers (acquired on eBay) monitor system status, and aim the antennas to track the Moon via an LL Grace Kansas City Tracker interface board driven by the NOVA for Windows program from Non-Linear Systems. WA2IKL photo

The initial main moonbounce exciter was a Hewlett-Packard high-precision microwave synthesized signal generator (bottom of stack), purchased for pennies on the dollar through the eBay internet auction site. Frequency stability is provided by an eBay-acquired atomic clock, and cross-checked on a digital counter (top, also from eBay) using a Trimble Thunderbolt GPS-locked oscillator as its frequency reference. N6TX photo

This Thunderbolt GPS-Disciplined Clock, donated by Trimble Navigation Ltd., provides the moonbounce beacon with frequency verification to a fraction of a Hertz. The donation was engineered by SETI League member and Trimble employee Art Lange, W6RXQ. SETI League photo

A cascade of solid state amplifiers from Down East Microwave Inc. brings the synthesizer's milliwatt output up to the 20 watt level. The power supply (bottom) came from eBay. Plans call for increasing transmitter power (see below), and running periodic tests at a variety of power levels (both higher and lower), to permit use by a wide range of receive systems. N6TX photo

This solid state power amplifier, built by well-known 1296 moonbouncer Harry Price, K3AX, puts out a maximum of 225 Watts CW. We placed it into service in February 2002, but at a reduced power level consistent with continuous unattended operation. Thus, it has brought the beacon's power level up to around 150 watts, for a +74 dBm EIRP. WA2IKL photo

The entire W2ETI EME Beacon station components mounted in a single equipment rack. At the top of the rack are the high-power solid state amplifier and the power meters for measuring the transmitter's output. WA2IKL photo

Just below the power amplifier is the exciter assembly, consisting of the synthesized signal generator, time bases, frequency counter and control circuitry. WA2IKL photo

Below the exciter assembly are the intermediate power amplifiers, and the programmable power supplies. WA2IKL photo

At the bottom of the equipment rack are the station control computers and antenna rotor controller. WA2IKL photo

The SETI League's W2ETI moonbounce beacon was out of service for more than a year, due to a failed power amplifier. In 2006 the power amp was replaced with this commercial half-kilowatt MOSFET linear amplifier from Kuhne Electronic in Germany. In the interest of reliability, we are operating the amplifier at reduced power (typically 350 watts). Kuhne Electronic photo

As part of the refurbishment of The SETI League's W2ETI moonbounce beacon, President and station trustee Richard Factor has created this web-based real-time status display, which graphs changes in transmitter forward and reflected power, power amplifier cooling air temperature, and Moon elevation angle, over a one hour period. SETI League image

After more than a year of downtime for refurbishment, The SETI League's W2ETI moonbounce beacon resumed operation in April, 2006, with a new exciter assembly, power amplifier, control computer system, power supplies, and UPS. Reception reports were quickly sent by K2UYH and K5SO. Eight new long loop Yagi antennas are planned for the next phase of beacon upgrading. WA2IKL photo

Remote telemetry monitoring of the W2ETI moonbounce beaon shows what happens when we operate the transmitter key-down for sustained periods of time. In this display, we integrate for one minute intervals, with time running from right to left (most recent minute on the left of the display, with each preceeding minute for the prior hour displayed to the right of the more recent one). In this test, the transmitter was operated at full power for seven minutes. Note that cooling air temperature increases stadily, the line changing from green to yellow to red; that forward power drops from 370 down to 310 watts; and that reflected power increases as the amplifier and coax heat up. Because of these negative thermal effects, we are operating the beacon at a low duty cycle (transmitter on for only the first minute out of every five). SETI League image

Out With The Old: The two quad-helix arrays long used in The SETI League's 1296 MHz Moonbounce Beacon were removed from service in June 2007, to make way for a new antenna system (see below) WA2IKL photo

In With The New: These eight 55-element loop yagis from Directive Systems were installed at The SETI League's 1296 MHz Moonbounce Beacon, replacing the old dual-quad helix array seen above. The additional antenna gain should make the calibration beacon detectable by a typical Project Argus radio telescope WA2IKL photo