Hem SAQ Forum SAQ Transmissions Alexanderson Day Transmission June 28, 2015 Patrik Eriksson – the mad inventor


Patrik Eriksson – the mad inventor (moved from comments)

I guess I am one of the closest listeners to the great alternator; just a wee bit north of Gothenburg. But, my receiving equipment is somewhat extraordinary – a self-built analog music synthesiser!
As the transmitter frequency is well within the bandwidth of my audio processing circuits I realised that they could possibly be used as a VLF receiver. One of the synthesisers VCOs were used as a local oscillator, tuned to something like 17,8 kc/s (btw, ‘the grand old lady’ is far more stable than my music oscillators. There is no room for a mammoth flywheel in here… :) ) A long wire as an improvised antenna was then connected through the synths preamplifer, then mixed with the VCO into the ring modulator unit (4-quadrant multiplier). The resulting signal at a few hundred Hz was then fed through a 4-pole low/bandpass filter and on to the loudspeakers.

Now, I’m just a musician and audio engineer with limited, to say the least, experience in antennas and frequencies above hearing range. I had a result, but just barely. With careful listening and tuning of the filter I could hear most of the transmission, but almost drowned in other forms of noise in my setup. My next plan is to spend the time until christmas transmission to learn and design a proper antenna, and a better (less noise, more gain) preamp cirquit.
Such a lovely reason to learn and look deeper into analog topics in this digitalised world!

Also, I have to admit to a wee bit of ‘cheating’; I did have the dutch SDR online too, as a backup plan / reference. 😉

I will stay tuned…




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