Comment by phkamp

2 years ago

He influenced my career as much as Dennis and Ken did.

Our "nanokernel" paper brought NTP into the nanosecond domain and gave FreeBSD "timecounters".

But our true shared passion was Loran-C

Dave even invented the 16-pulse "tactical Loran-C" during the Vietnam War.

I borrowed his ISA card Loran-C receiver (serial #1 & only) and later I built two generations of SDR receivers, and he was so proud when I showed him this dancing pulse received with a cheap ARM chip:

https://phk.freebsd.dk/AducLoran/animation2.gif

And boy was he pissed when USA shut down Loran-C, he really loved his "loudenboomers"

RIP

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phkamp

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TedDoesntTalk  2 years ago

What is the difference between Loran-C and tactical Loran-C? I googled "loran-c vs tactical loran-c" but did not come up anything. Thanks.

  • phkamp  2 years ago

    Tactical Loran, also known as "Loran-D" was a concept Dave was involved in during the Korea war. There's a pdf about it somewhere on the web.

    Remember: This is way before GPS, so pilots could not just look at an instrument and know where their plane was, and many planes, both civil and military would regularly get lost (in the meaning: loose track of where they were).

    In friendly skies you could have your own Loran-C, but you couldn't expect the enemy to provide that for you, so "tactical" meant that you could rig up a naviation chain where you needed it, in a matter of days.

    (In the end both USSR and China set up Loran-C chains, some of them operating jointly with the US chains, and today the Rusian "Chayka" and possibly the chinese chains are the only ones left.)

    So tactical Loran was basically Loran-C transmitters in containers or trucks, and because they would be much weaker than real Loran-C, being both power constrained and having much smaller antenna, they used a 16 pulse code instead of an 8/9 pulse code.

    Loran-C&D is spread-spectrum transmission, but decades before the theory was fleshed out, but it was well understood that a longer pattern would improve S/N.

    But Loran-C/D was just one of many DoD radionav systems that project 621B (=GPS) was supposed to kill, and eventually did kill.