 achieved a rough average of 17 dB improvement over FSK against jamming in the presence of multipath, justifying transition to an F9C-A production phase. PHIL MOVED YESTERDAY MOST OF HIS JUNK THAT IS THOUGH HE IS STILL AT ROBINSON RD THERE IS NOT TOO MUCH DOING AT THE LAB AT THE MOMENT WE ARE TRYING TO FIND EQUIPMENT FOR THE ATLATIC PULSE TESTS THE IPSWICH SITE IS COMING ALONG SLOWLY BECAUSE OF THE LONG DELAY IN STARTING MARIE WILL BE FLYING OUT TO SFO ON MONDAY SHE SAYS R THAT SKE WILL GIVE YOU A CALL WHEN SHE GETS TR THERE 1 DONT KNOW IF SHE HAS A JOB YET RGR I WAS WONDERING WHEN SHE WOULD ARRIVE OUT HERE AND ALSO IF I COULD BE OF ANY ASSISTANCE TO HERE I WILL WAIT FOR HER CALL AT EDL ON MONDAY IN REGARD TO MY OWN PLANS I PLAN TO STAY OUT HERE UNTIL THE FIRST EQUIP AT EDL IS SHOWN TO BE OK AND THE IF TIME PERMITS WILL GO BACK TO THE LAB FOR A SHORT STAY IT WILL BE SHORT SINCE I AM GOING UP TO TACOME TO BE MARRIED ON THE 25 OF AUGUST AND THEN I PLAN TO GO TO SWEDEN ON THE 20 OF SEPTEMBER FOR AT LEST A MONTH so I WILL BE ON VACATION FOR ABOUT THREE MONTHS GA OH REALLY " WE ARE ALL BREAKING OUR NECKS TRYING TO GT GET AT THIS MACHINE TO SAY CONGRATULATIONS AND KER I EXPECTED PITY MMMMMM WELL THIS IS RATHER SUDDEN AS THE GIRLS SAY HELLO BOB THIS IS P GREEN I KNEW IT WOULD COME TO THIS SOME DAY CHEER UP THE SORST IS YET TO COME CONGRATULZYIONS YES I UNDERST $ 5-5 {BATISREEDSEYTMOUNSHOULD HOPE FOR THE BEST AND BE SATE SATISFIR SATIS AND BE SATISFIED WITH THE WORST GA Figure 2.22. This duplex teletype output, made during coast-to-coast tests of the F9C system, includes undoubtedly the first wedding announcement afforded the secu- rity of spread-spectrum communications. (Copy courtesy of the announcer at the West Coast station, Robert Berg.) The Historical Origins of Spread-Spectrum Communications While initially the F9C MARK-SPACE modulation was FSK, this was eventually changed to another, equally phase-insensitive form of orthogo- nal signaling, which might be called the "mod-clock" approach. The mod- clock format, co