Re: Simple spectrum analyzer for pre-compliance

Rich Grise hath wroth:

Kinda reminds me of the rotating color disk TV standard proposed by CBS in about 1947. It works, but who would want to use it?

It's not quite that easy. There are plenty of articles on the internet for converting a television into a really awful oscilloscope, but not the other way. I first did it in college (late 1960's) using and RTL, DTL, and DCL sync seperator. It was all part of Learn By Destroying(tm).

I found very few articles on the topic with Google. Looks it would make a good student project.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Would have created a whole new profit center in industry, the TV lube and tune.

It was done a lot in ham radio. Many folks will remember slow scan television. If you were remotely related to the Rockefellers you'd obtain a surplus scope with a slow decay tube. If you weren't, then you got said tube at a flea market and built a crude scope. Around that the sweep generator and sync was built, plus the signal path filtering and demodulator.

The high voltage generation was a bit of a challenge with 1970's parts. Many a fine circuit came to grief in them days. The worst case was a guy who managed to zap a HV jolt onto the +5V rail in his VME-style Eurocard rack which contained all kinds of other circuits as well. It toasted literally every single IC in there. The only thing that was still working was the little lamp inside the power switch.

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Regards, Joerg

http://www.analogconsultants.com

What was amazing was that it actually did work. RCA had a hell of time demonstrating a functional CRT system, mostly because they were really pushing the state of the art. The only reason the CBS system was seriously considered by the FCC was that none of the other proposed systems were functional at the time. I don't recall the exact dimensions, but a 19" color TV would have required something like a 15ft diameter color wheel.

Please. Just thinking about it gives me nightmares from projects long dead and buried. I was involved in one of the numerous abortive attempts to develop a sellable picture phone. The basic problem was to design a system that could shovel video over a really awful phone line, with incredibly bad group delay, and without adaptive equalizers or echo cancellers, and still have enough bandwidth to sneak voice in between the frames. It was one of the few projects where the engineers gave up before the customer fired us. At this stage, my design abilities were limited to stealing test equipment and raiding the stockroom for parts, for the engineers. Incidentally, this was just after the Carterphone decision (1968?) which required that we had to acoustically couple the video to the phone handset. Banging the carbon microphone to loosen the packet granules was the first step in the operating instructions.

At one point, I tried to replace a TV flyback with an automobile ignition coil. It didn't work, but the sparks and smoke were certainly impressive.

In the early 1960's (High Skoll), our radio club built a SSTV system using most of a donated commercial fax machine. The original used a huge sheet of photosensitive paper and a flash tube. We modified it to use a drafting pen and solenoid. It didn't do photos very well, but the various weather maps and over the air news broadcasts were quite readable. The only real problem is that the monster had a mechanical drum speed adjustment with no synchronization. Skew and drift were a constant problem. I kinda miss the days when I had no idea what I was doing and never let that stop me.

Nice. I'll spare you my damage report of equipment destroyed. (Note that my domain name is Learn By Destroying). My all time high was a

4Kw NMR (nuke magnetic resonance) power amplifier, which used 8ea VMOS power xsistors. These were something like $200/ea in 1979. Although the devices were claimed to be unconditionally stable, I managed to find a source and load combination which sent the amplifier into oscillation. That blew all 8 power xsistors, sending ceramic shrapnel bouncing around the rack (with my head still inside the rack).

High voltage is always fun for destroying small signal devices. However, for really impressive fireworks and destruction, high current is much better. Nothing like watching a steel crow bar turn bright red and vaporize after being dropped on the -48VDC battery terminals. If a fuse blew, the fuse cabinet was usually replaced along with the fuse.

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558            jeffl@comix.santa-cruz.ca.us
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS

So you'd need a new house along with that TV. Oh man. What would have happened if that wheel went out of balance?

Ah, a "stench fax"? A stylus hovered over sensitive paper and arced away stuff to write. After a few pages the air in the room became unbearable. Who knows what was in that air.

Hopefully that wasn't beryllium oxyde ...

But HV created that impressive bang when something went.

--
Regards, Joerg

http://www.analogconsultants.com

Joerg hath wroth:

Not much. Most of the original versions were intended for the 9" round displays of the late 1940's. The wheel was located inside the cabinet for safety reasons. There were "scanning adapters" that converted B&W sets into color TV, which were external. The disk was fairly light weight, which served to reduce damage, injuries, and fatalities. The only big external wheel was the monster that RCA dragged into the FCC hearing room to demonstrate how badly the CBS system scaled.

Despite the obvious disadvantages of the CBS system, it has several major advantages.

1. It was cheaper than any of the others.
2. It was using a known technology (Nipov scanner).
3. The pictures were absolutely gorgeous compared to the RCA "dot sequential" system.

(Who needs HDTV anyway?)

1. It can be used to "convert" a B&W TV into a color TV.
2. It can be resurrected from the dead today by using 2-5msec persistence LCD screens.

CBS eventually gave up on color wheels and switched back to their earlier "field sequential" system, but piggy backed on the RCA/NTSC system in order to insure B&W set compatibility. Field sequential also produced color better than RCA's dot sequential:

Note the "scanning adapter".

You might find the chronology of the CBS system and the FCC hearings of interest. Nobody wanted the CBS system, but everything else was a kludge:

Nope, although I did own WXFAX contrivance that used spark gap imaging. If you do it right, you can set fire to the paper. It worked best with a small spark gap and Thermofax paper. I don't recall any smell other than the usual toxic ozone stench and vaporized heavy metal smog. Somewhat earlier, I ran the college print shop. We used a Gestetner stencil cutter for the mimeograph printer, which used a spark gap to blast holes in the stencil. I'm not sure what they did different, but there was very little smell, and no smoke.

The contrivance I helped resurrect was basically a rotating pen plotter. I took a Koh-i-noor drafting pen, feed it with a reservoir full of India Ink, and uses a solenoid to move the pen up and down. The major challenge was to not spray ink all over the place, which was partly solved by using the smallest 00 or 000 pen available. Unfortunately, it would usually clog if left standing for more than a few minutes. I think I was 16 years old at the time, so please don't expect much in the way of engineering elegance.

It was. Lots of ceramic fragments flying around. Fortunately, the power amp wasn't running long enough to get them hot. Still, I had a few small cuts and piece of ceramic imbedded in my face. The attendant crowd was debating whether to drag me to the local emergency room, or to complete my execution in retaliation for destroying the last remaining VMOS transistors. While they debated, I picked out the pieces of ceramic with a tweezer, and fell asleep under my desk. Since the employee handbook does not cover murdering sleeping employees, I survived.

Bah. Real devastation can only be appreciated by the overwhelming application of power, not voltage. Hot slag spewing from the shorting bar. Melted copper and immolated components. Burning components, circuit boards, and insulation. While admittedly, high voltage can destroy a greater variety of devices and components, truly massive and permanent devastation requires lots of watts.

Remember: Learn by Destroying, which means if you haven't destroyed it, you don't understand it.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Jeff Liebermann hath wroth:

More... Photo of a CBS converter:

The CBS system wasn't the only color wheel. In 1955, we were blessed with the Col-R-Tel spinning wheel system:

and others:

Incidentally, the CBS wheel spun at 1440 rpm, while the Col-R-Tel system ran at 600 rpm.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558