[Lowfer] spark microwave transmitter

Sun, 3 Aug 2003 20:57:10 -0400

Funny that this should come up on the Lowfer group. Good to see interest
along these lines. I have been playing with generation of micro-,
millimeter- and submm waves by spark and various simple detectors including
neon lamp plasma diodes (just a common glow lamp). Loads of fun and very
informative to see what things are opaque or lossy, what things are
transparent, reflections, standing waves, simple wavelength measurement etc.
Anyway, this kind of thing has been discussed quite a bit on the microwaves
reflector but this is a first for an ostensibly LF group (not that I'm
complaining mind you :-) Then again, I also experiment with still higher
freqs, i.e., optical, so uwave is by comparison practically "LF"...
The URL for the J.C. Bose site is
http://www.tuc.nrao.edu/~demerson/bose/bose.html Very interesting read.
That suggestion using the piezo to vary the cavity dimensions at an audio
rate thus creating FM is brilliant, I have to go try that now!!
73 de Jon W2MXW

-----Original Message-----
From: Ed Phillips <[email protected]>
To: [email protected] <[email protected]>
Date: Sunday, August 03, 2003 8:18 PM
Subject: Re: [Lowfer] spark microwave transmitter

>[email protected] 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
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