[Lowfer] spark microwave transmitter

[Ed Phillips]

riese-k3djc@juno.com wrote:
> 
> Actually the first experiments using spark to generate RF
> were on UHF frequencies. It is still a pretty noisy broad banded thing
> GunPlexers which are self oscillating are narrow by comparison
> there is some joking about using spark to generate Micrometer waves
> not sure what the upper end of allocated RF is,,,,,, 300 Gig  ?? but the
> boys
> that play around up there can work some distance with little RF. Spark
> generated MW
> energy up there should be doable
> 
> How about spark generated ELF say at 3000 cycles  ??
> 
> Har
> 
> Bob  K3DJC

	The latter is entirely reasonable.  At one time Marconi used a "timed
spark discharger" to generate a pseudo-CW signal.  Very fast rotary gap
with one spark per cycle of RF.  That would be a snap at 3000 Hz.

	Hertz's first work (ca 1886) was at 50 MHz but he realized that the
limitations of the space he had available required a higher frequency so
he moved up above 300 MHz for a lot of his work.  The most amazing work
of that time was by an Indian Physicist by the name of Bose, who did a
lot of very good work at about 60 GHz using a small spark gap in a small
waveguide with rectangular horn radiator.  His work is available on the
web (address is at work) and he was widely acclaimed at the time,
presenting several well accepted lectures in England, but later sort of
fell into history's crack until the last 20 years.

	Next interesting VHF work was by the German inventor Christian
Hulsemeir (spelling is a bit off) who, around 1904, built a working UHF
ship-detection RADAR for collision  prevention, using a spark
transmitter, coherer receivers, and parabolic cylinders.  He received a
patent for his work and demonstrated the device successfully to various
naval interests, but it was never adopted because of the widespread
growth of "wireless", which was much longer range and easier to install.

	Several people generated millimeter waves with sparks during the period
up to perhaps 1930.  During WW2 the Germans built a VHF early-warning
radar using a very high power spark transmitter (Megawatt class), but I
haven't been able to find out much about it or how successfuly it was. 
Later in the war they also built a 10 cm radar jammer using a spark gap
in a waveguide.  Can't find much about it either.

	There are reports of someone who built a spark "oscillator" which had
such low damping that the wave train lasted "20,000 cycles".  Again, not
much dope available or proof that was really true.

	For those who want to play around with VHF spark transmitters it's very
easy to do and good entertainment.  I've built a 300 MHz transmitter
which, with crystal detector and opamp audio amplifier, works out to
about 50 feet or so.  Easy to observe reflection off a metal sheet.  I
also built a 3-element yagi which worked.

	There are lots of things to play with in this world.

Ed