On Aug 29, 10:06 pm, "Michael Koblic" wrote:
"Jim Wilkins" wrote in message
On Aug 28, 11:51 pm, "Michael Koblic" wrote:
"Jim Wilkins" wrote in message

Judging from your e-mail address you will understand how electronics were
done by amateurs before the advent of the black boxes. Except we did not
have black boxes: we had Wehrmacht surplus. And ingenuity. And fire
insurance...

We had plenty of US mil-surp gear to play with too. The aircraft stuff
often ran on 400 Hz AC and operated on 225-400 MHz which is military-
only here.

I used to have a working copy of a German aircraft-detection radar
transmitter from 1931(?) sitting on my Mac's monitor. It consisted of
a high-voltage transformer and a spark gap. The two spark gap
electrodes formed a dipole about 100mm long. There was enough lead
wire connected to it that I wouldn't predict the frequency and I
expect it was broadly tuned, but it could have been over 1 GHz. When I
rescued it from a lab I was closing down it was in an aquarium tank
because it was so dangerous. I removed the power cord. Spark gap
transmitters are illegal to operate now anyway.

As I understand it, the receiver was shielded from the transmitter and
only received the CW signal when it reflected off an airplane.
Detecting the audio-frequency Doppler shift in the return seems
unlikely for biplane speeds and spark-gap bandwidth and it goes away
as the plane approaches.

In "The Wizard War" Dr Jones wrote that early '40's German field radar
transmitters were as stable in frequency as the best British lab
standards, apparently because they could grind quartz crystals better.
He certainly had a lot of respect for German equipment. Then again,
the British chose to use American aircraft radios rather than their
own. As with Russia and Japan their theoretical and lab work was
excellent but they had trouble mass producing it.

but the transfer punch/paper roll method beats it every time particularly
for small parts.

That's a good idea I hadn't seen before.

Ha! You heard it here first!

The traditional center punching tool looks like a funnel with the
center punch sliding in the spout.

These are a gold mine of information;
http://www.amazon.com/Hand-Simple-Tu...s-Practice/dp/
0486264289/ref=sr_1_3?ie=UTF8&s=books&qid=1220099472&sr=1-3
If the link is broken, Google for "Holtzapffel"

The yellow one concentrates on turning and should answer your
questions very well, the red one is about hand tools and the history
of screw threads. I don't have the other books yet. They describe
Victorian-era technology in exquisite detail from a master toolmaker's
perspective and often give the inventor of our common tools, for
example Mr. Hale registered the centering square in 1862, Holtzapffel
and Deyerlein began making 3-jaw self-centering lathe chucks in 1811.

Like anything German they are ignored in most English-language history
books although they worked in London since 1787 and helped train
Whitworth. "English and American Tool Builders" gives them only a
paragraph. The Holtzappfel books complement that biographical one by
showing their work.

Jim Wilkins