[NLRS] Who's the computer programmer in the bunch?

[Dr. Gerald N. Johnson]

On Sat, 2006-07-01 at 22:51 +0000, Donn Baker wrote:
> 
> Let's see... and you set the gap to how many thousandths on WHICH spark
> transmitter....

Probably, had I ever had need for setting the gap on a spark
transmitter, I'd have set it for the best echo from the neighbor's barn
a mile away...

The Collins 821A-1, 250 KW that I worked on for VOA (I was at Collins),
had three spark gaps. One set to hold off 1200 volts, the other two to
hold of 15 and 30 Kv. Each was supplied with a tungsten needle. When it
was time to shut the transmitter down quick, a thyratron put a 50 Kv
pulse on the needle and the voltages in those supplies was dissipated in
that arc until the overload relays could pull open the vacuum
interrupters on the the big transformer primaries. Nearly every one who
was near the power supply (fenced in but outside) floated back down from
a foot in the air without having bent their knees when that event
happened. It was a regular task to rotate the chrome plated brass balls
to present a smooth surface for the arc and to replace the tungsten
needles. And we had a stock of 2" brass balls because the arcs did
damage the entire circumference eventually. It took some 40 milliseconds
for the relays to open the vacuum interrupters. Eventually our
substation transformer objected and blew its lid. It couldn't be
rebuilt, the core laminations were welded together by the failing
windings.
> 
> I missed the IMSAI8800, (circa 1974-75) but I did build a "Jolt" (Several,
> actually), circa 1975-76.  6502 processor, 256 bytes (notice, NO 'K' or 'M'
> after the number) memory, TTY interface and a video monitor interface.
> ~$400, if I remember correctly.  A 4KB memory board was ~$300.  Static
> RAM... about 8 amps at 5 volts, IIRC.

The 6502 had some good things and some bad things. I considered it a
RISC chip. Reduced Instruction Set Computer and after programming the
Z80, programming the 6502 was frustrating for all the extra code I had
to include to do what the Z80 did in one instruction.
> 
> I was at the University at the time, and we used a couple of them for
> teaching Process Control, as opposed to "programming" and such.  Its
> amazing how much can be done with little memory and assembly-level code
> when you don't multiple megabytes just move a mouse.
> 
> Its also amazing how much trouble a student gets into (or the "pro's," too,
> for that matter) when the code does what they TOLD it to do, not what they
> THOUGHT it would do.  

I live and die by the debugger these days and each line I ask, "Is that
what I want?" Sometimes its yes, sometimes its no. Then I work over the
code some more.
> 
> Best demo is to pump a quart of water from a 5 gallon bucket into a two
> quart measuring cup.  And they have to clean up what gets spilled.  It
> usually gets done correctly after the first failure.  Messy clean-up work
> is such an incentive.
> 
> 73 Donn
> WA2VOI/0
> 

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer