Thursday, August 24, 2017

Flex Remote @ ARRL HQ

After a false start or two, we finally have Flex Radio's Version 2 SSDR software running.  It enables easy internet remote operation from wherever, using my Flex 6500 radio installation at home and the Maestro controller.

My first successful test was using an "outside" test internet connection via my Nexus 5X cell phone in "tethering" mode, while I was still at home.  It was convenient to have both local and remote sides of the connection on my operating desk.  (With my data plan, I estimate the hourly running cost for remote service is about $6/hour with standard settings and not minimizing bandwidth.)

Today, we are set up in the ARRL headquarters site in Newington CT, about 40 miles from home as the crow flies.  Everything seems to be working well.  "59" reports from Switzerland and Spain.

At home, I have the Flex 6500 controlling the tuning of my SteppIR 3-element beam (fixed on Europe), so I can remotely operate from 20 meters down to 6 meters.  Unfortunately, there is no remote pointing control -- yet.  Also, no integration with digital modes or my logging system.  One step at a time.

Wednesday, August 09, 2017

What we were doing in the 80's (VLBI)

Arthur Niell, Marshall Cohen, David Rogstad, and Martin Ewing, ca 1982

See full photo album.

PDP-11s were hot.  Helical scan video recording was just the thing for recording high-speed radio interferometer (VLBI) data.  In a Caltech-JPL collaboration, we built what was then the largest correlator to process data streams from up to 5 telescopes at once -- providing correlations (fringes) between all 10 pairs.   Getting any fringes at all required delicate synchronization of the telescopes (Loran C timing and Hydrogen maser frequency standards).  Geometric corrections were tricky, too. You had to know the baselines between telescopes accurately, giving the delay and doppler frequency offsets.   To manage all this, we had MSI-TTL logic, core memories, a PDP-11/40, and Forth software.  The hardest part -- keeping those tape machines running!  They were modified IVC and Ampex helical scan recorders, semi-professional.  A later version of the system used standard consumer VHS recorders, which were just becoming available.

One bit sampling was the choice for best signal-to-noise ratio on a broadband "continuum" radio source.

All this came to light again when I started digging into some old files.

When all else fails...

My Keuffel & Esser Decilon 10, model 68-1100 slide rule.  There are lots of K&E sites. For example, this one.