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From: "Peter Martinez" <peter.martinez@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <000001c699d3$5da1ecc0$e6a4c593@RD40002> <002301c699e3$9f270bc0$e7ce28c3@captbrian>
Date: Tue, 27 Jun 2006 13:00:13 -0000
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Subject: LF: The sound of spark
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>From G3PLX:

The nearest thing still around that must sound like spark, is LORAN. After 
all, it is generated in exactly the same way. The only difference is that 
the LORAN megatron is driven with 6 pulses at 10uS intervals - that is, a 
burst of 6 cycles of 100kHz - whereas the spark transmitter only had a 
single spark per emission.  In both cases the RF envelope would have risen 
more rapidly than the rise-time of the maximum audible frequency, so the 
signal must have sounded very similar in the headphones. Indeed, the 
envelope waveform of the experimental spark transmitter shown on the VE2CV 
website is almost identical to the waveform of a LORAN pulse shown on the 
Loran website.

If you listen on 100kHz with the receiver on AM, apart from the 
low-frequency pulse-rate at the basic p.r.f. between 10 and 20Hz, you will 
hear a 'squeekiness' to the sound, which results from the fact that the 
basic pulse is actually a burst of 8 or 9 'sparks' at a 1kHz rate. If the 
basic spark transmitters were 400-600Hz, they would have sounded lower in 
pitch than this 1000 Hz squeek, but the harmonic content would have sounded 
exactly the same. LORAN is effectively transmitting strings of 9mS spark 
transmission dots.

A simple spark transmission on LF would have had a bandwidth determined 
almost entirely by the antenna resonance, but I imagine that as 
transmissions were taken higher in frequency they would have become rapidly 
wider and wider, unless steps were taken to narrow-down the emission by 
means of extra tuned-circuits. Whether this was ever done or not I don't 
know. There would have been good reasons to keep the bandwidths of 
transmitters and receivers roughly the same.

73
Peter