I first met Don in 1971, my first year of grad school at UVa and he was on his NRAO PostDoc.
He was always willing to chat and support a callow grad student.

I remember two experiments he did over the years in Green Bank with especial awe because, as usual for Don,
he used equipment in extremely novel ways.

In the early 1970s he followed *individual* pulsar pulses in frequency by using all 5 GB telescope independently
tuned to different frequencies (the 140 ft, the 300 ft, and the 3 85 ft interferometer elements).  This required
writing a complete operating system for the interferometer which had never at that point been used as
individual telescopes tuned to different frequencies.

In the mid 1980s he studied giant pulses from the Crab -- these things are 103 stronger than the mean pulse
intensity but are both infrequent, say, 1/5000, and sporadic.  His pulsar back end in GB had finite bandwidth of
course and, in those days, finite storage capacity.  So he couldn't just crank away and observe continuously.
His solution was to team with Tim Hankins who observed the Crab at L band at the VLA which had a mode
where they could observe constantly albeit at low resolution.  When Tim found a giant pulse, he sent a
trigger signal to Don at the 140 ft *over the Internet* so he could turn on his pulsar backend to sample
at 800 MHz with 85-2.  To make this work they had to synch the clocks of
their computers for days, again over the internet, taking out packet speed fluctuations by polling many,
many different clocks around the internet.  At least that is what I recall.

As Jim Moran said in Physics Today, we are all much poorer now from the loss of his humanity as well as his technical gifts.

i had been working for the Astronomy Department only a short while, when Don thought it would be a good idea to take the new hires up to Hat Creek Radio Observatory for a look around & to meet the staff there. I jumped at the opportunity to leave town; what could be better than to be in Mount Lassen country? Don, Robert, Andrea, & I met in the early hours downtown Berkeley & headed north. Once there, we had a staff meeting & now were able to put a face to the names of people we had been working with via telephone/email.  Susie & Don took us around in the Jeep & gave us the grand tour, Don trying his best to explain in layman terms just what was going on up there; yep, a little hot & arid, but beautiful country all around. Susie advised checking out Burney Falls, where we took a hike and considered jumping in the lake nearby. We luxuriated in our surroundings; exploring the lava tubes, taking beautiful moonlit bicycle rides in the middle of the night.On our way back home, we tried to climb Mt. Lassen, but being a little unprepared - such as trying to scramble up steep icy inclines in tennis shoes - proved to be too much, so we had to, most unwillingly, let it go...I still find it very difficult that someone so vital and engaged with life and those around him could be so suddenly gone from us. I will miss him, more than I can say.

nina ruymaker 

 In the past 5 years, I attended "executive Dept meetings" weekly with Don, while he was Chair of the Astronomy Dept. and then when he was the Director of RAL.    Of all the discussions, visions, budget troubles, restructuring, struggles, and conflicts that arose in those meetings, one thing stands out far above everything else.   Don was always finding ways to improve the communication, coherence, and collegiality of the astronomers in Berkeley.  

He always had a new organization in mind that would join everyone together to makes us  more than the sum of our parts.  "BACI" was the name of his beloved organization that brought Berkeley Astrophysics together.   He loved the idea that if people worked together they would be more creative and productive, and enjoy their work more.    He appreciated that people working together, rather than separately, was the key to unexpected innovation.    

He similarly took the Department's decadal Academic Review to heart, spending countless hours constructing that document, always involvilng everyone in the process.   He similarly encouraged  a diverse but coherent group of radio lab, digital electronics, and radio telescope design efforts, always thinking that some FPGA-type or DSP-type widget would emerge when folks with different expertise interacted.    And the new Campbell Hall project brought all of this together as Don constantly encouraged the architects to design interactive areas for astronomers to chat and bridges to allow cross-fertilization with physics.   Collegiality and interaction were dear to Don.   I've learned a lot from his patience, kindness and people-oriented science.

Almost ten years after I left Berkeley, and working in Canada (U.Waterloo) I happened to be wandering along a deserted beach on Cape Cod... There was one other person in the far distance walking towards me and as he approached I thought there was something familiar about him.  Eventually he was close enough that I recognized that it was Don.  I was surprised and even excited by the coincidence, both of us far from home meeting on an otherwise deserted beach...  but Don seemed to think it was the most natural thing.  It was a typical, very laid-back Don reaction.  We chatted as if it had been hours rather than years since we had last crossed paths.  I'll never forget how Don exuded this sense of such things as being inevitable, and one just goes with whatever life brings.

On behalf of Associated Universities, Inc. and the National Radio
Astronomy Observatory, I want to express our sincere condolences to
the family and friends of Don Backer, and to his colleagues at
Berkeley.  Don was a friend and colleague of astronomers around the
world, including many at the National Radio Astronomy Observatory and
on the AUI Board of Trustees.   He had a close and longstanding
association with AUI and NRAO spanning his career, including a
post-doctoral position at NRAO, his pioneering work in Very Long
Baseline Interferometry (VLBI), his participation in AUI committees,
and his current leadership of PAPER.  He was the Karl G. Jansky
Lecturer in 2003.
 
Many of us had close interactions with him even in recent weeks,
given his involvement in so much of radio astronomy.  I myself had
long discussions and dinners with him at the June US SKA Consortium
meeting in Washington and at the LOFAR inauguration in The
Netherlands, where we discussed the future of radio astronomy in the
US.   
 
All who know him, and there are many, recall his kindness, his
thoughtfulness, his energy, and his integrity, as well as his passion
for science.  He was highly respected in the astronomy community, and
his untimely passing is a true shock to all who hear.  Don will be
missed. 
 
Ethan J. Schreier,   President
 

Don and I had only a few glancing interactions from the time we were engineering physics students at Cornell until one memorable day in 1982.  On that day I pulled my rental car into the parking lot at Arecibo Observatory, thankful to have survived the mountain roads (at that time they were still new to me).  I stepped out of my air-conditioned vehicle and was assaulted by the heat and humidity of the observatory.  I quickly headed into the administrative office building and was temporarily unable to see in the deep shade of the stairwell.  Thus I literally ran into a wild man.  Don’s eyes were the bright twinkly blue we all recall, but they were surrounded by massive amounts of redness because he hadn’t seen a bed in a long time. His hair was disheveled, his clothes were worse, and he had totally lost his voice.  Don croaked at me “642 Hz!” and I stared back at him blankly.  I was clueless.  Don noticed.  We moved up a few stairs so that Don could take a long drink of water from the drinking fountain on the landing and then, with many hesitations, squeaks, and an extraordinary amount of body-language, he told me about this mystery radio source.  He told me that against all odds (and certainly against the combined wisdom of the astronomical community) the mystery source had turned out to be a neutron star rotating 642 times a second – the first millisecond pulsar!  That day Don shared with me the enormous excitement, joy, and satisfaction of science done well.  His jubilation had nothing to do with ‘see, I was right!’ and everything to do with wonder and amazement that the universe contained yet one more exotic object that we could study in detail, and learn from in turn.  That day Don imprinted on me a model of how to do good science and how to be a good person.  I believe one of the reasons that Don delighted so thoroughly in working on new instruments with students is because he always hoped that he might assist one or more of them to experience that same excitement and the pleasure of discovering something new about the universe.  As Aaron Parsons has now shared with us, only days before Don was snatched away from us, he may have done just that - again. 

It’s always hard to lose a colleague, harder still to lose a friend, but hardest of all to lose such a good guy.  I agree with Don’s wife Susan’s assessment, “Don was the goodest.”

 I’ve probably known Don longer than almost everyone in the astronomical community, so I thought I’d pass along some thoughts on Don’s life in some of the years before astronomy.  Don and I became friends at the beginning of freshman year at Cornell in 1962 -- 48 years ago.  Those who got to know him as a fully formed adult may be surprised to learn that he was a frat boy on a campus where most of the undergraduates joined fraternities.  Don’s was Phi Psi.  In those days, some of the fraternities made “Animal House” seem like a monastery, but as you might imagine, Don passed his undergraduate days with considerably more probity than the character played by John Belushi.  But not entirely.  Don was and stayed all of his life a child of the 60s.  In those days, like the rest of us, he danced to “I wanna do it” by Bobby and the Counts, a local Ithaca favorite, inhaled, and developed the fine sense of fairness and liberal outlook that he carried around with him the rest of his all too short life.

Don was a swimmer for the first two years, and I was amazed that anyone could swim competitively and still do physics at the level Don did at Cornell.  After all, we were in the engineering physics program that produced Carl Heiles, Frank Drake, Jill Tarter, Peter Goldreich, and a long list of other (mostly radio) astronomers.  Eventually, Don felt he had to choose physics over swimming and we’re all better off that he made that decision. 

Don stayed at Cornell for graduate school working with Frank Drake and spent a year at Jodrell Bank honing his skills in instrumentation and observation.   I was envious that he was able to do something so exotic in graduate school, but it was in the days before my own astronomy genes expressed themselves.  Don and I lost touch for a number of years, but were reunited when I started my postdoc in the RAL at Berkeley.  At our first lunch at the faculty club, I asked him what he wanted to work on, and he told me that there was this funny point source, that had all of the markings of a pulsar, but didn’t pulse, and he wanted to track down its secrets.  It took him three years, and it turned out to be the millisecond pulsar.  If it wasn’t clear before, it became immediately obvious to all of us around him that he had a nose with an uncommon sense of smell for the right astronomical problems.

I will miss the friend and colleague with whom I could share my excitement about research and some occasional secrets.

Don came from the great tradition of radio astronomer-engineers that is becoming increasingly rare.  For the longest time I could not figure out why he used j for sqrt(-1) and was always talking about octaves and decibels!  But I remember most his enormous patience and humility, and the undivided attention he gave to students.  He always preferred substance over style, and worked tirelessly at everything he did.  I learned a lot during the years I worked with him (1995-7), not just about pulsars and the odd cast of characters that "times" them but also about the tremendous attention to detail needed to carry out long-term projects.

It is no small tribute to Don that I'm still in graduate school today, as that was not obviously going to be the case before I joined his group year ago.  He had incredible humility, always able to make my contributions feel valued while simultaneously pushing me to accomplish more.  This is a tremendous loss for all who knew him, and I will miss him greatly.