This multi-mode transceiver is computer controlled and includes waterfall display and EME friendly functions including: AZ/EL display, Auto Doppler shift of Rx, Auto echo display and the FSK mode called PUA43, which was used for this QSO. The system's ability to dig into the noise results from long-term integration, separating signal from noise.
With this as background, "PUA43" is the transmission of up to 43 tones, one at a time. Each tone represents an alpha or numeric character. Characters must fall into a spectral bin, adjustable from 2 to 9 Hz wide. Each character's tone is sent for 2 seconds and repeated once or twice per minute for long as one wishes. To further improve reliability, there is a random frequency "stir" to eliminate the effect of birdies. This requires that both sked stations have their computer clocks synchronized. The Frequency accuracy was accomplished via a GPS controller (July 98 QST) steering a 10 MHz VCXO. Output of the OSC is buffered and power divided to feed the DSP-10 transceiver and "lock" the 23 cm txvtr. Unlike many FSK systems, this is not an all-or-nothing copy of text. A process called "message estimation" is used to determine the most likely characters. The confidence level of a received character is noted by it's color and improves with integration time.
The improvement over aural copy is yet to be fully established, but various experiments (non- EME) have shown it to be 20 dB or more, depending on the operators patience. The software to implement these EME functions is still in Beta test. However, Bob is close to a formal release.
One problem experienced during this 1st EME QSO was error between predicted and actual Doppler. Both W7LHL and W7SZ had to correct by 9 Hz to be in sync during the contact. This correction was established via the Auto Echo mode prior to QSO. A 2nd "FSK" QSO between W7LHL (10' dish) and W7SZ (12'dish) was completed on 18 Jan. Both stations again using 50 W. However, based on the margin, QSOs should be possible at significantly lower power levels.
More tests are planned.