Drambo for amateur radio: VLFReceiver
Between 1972 / 73 Mike Oldfield recorded Tubular Bells at the famous studio "The Manor".
Located 60 Km from The Manor was Rugby Radio station, a Longwave and Very Long Wave (VLF) transmitter of the UK government, that was mainly used for transmitting time signals and for submarine communication.
During the recording of Tubular Bells a test transmission from the 16 KHz VLF transmitter (Callsign GBR) was accidentally picked up by the recording equipment and made it into the master.
I have created a Drambo project that emulates a dual heterodyne VLF receiver. Load your TubularBells into the FlexiSampler and hear the morse code. MP3 files don’t work well. It’s best to use a WAV file directly from CD:
https://patchstorage.com/vlf-receiver-a-drambo-for-radio-amateurs-project/
Comments
Bizarre, I have also been experimenting with an FM and AM demodulator recently (with no success!). I don’t have a test file to try in here, but just as a processing tool it’s quite interesting, especially in non-melodic material.
That’s interesting. How did you approach FM demodulation? I once tried to build a PLL in Drambo but did not succeed. Maybe Drambos pitch detector module can help.
You need feedback to control the pitch of an oscillator.
If I remember correctly, by feeding the FM signal into a filter with slightly higher center frequency than the carrier, the output voltage will follow the modulator.
That’s the slope detector. They usually use a high pass filter for demodulation. It has one big weakness: It demodulates AM as well. Specially for radio this means loads of noise.
What now comes to my mind is a form of “Dramboised” Quadrature detector / coincidence demodulator. A very short delay or an all pass filter could create the phase shifted signal. Here is an interesting article about FM demodulation that describes quadrature detectors: https://www.electronics-notes.com/articles/radio/modulation/fm-frequency-demodulation-quadrature-coincidence-detector-demodulator.php
@catherder Yeah cool, you're right!
Here's one possible implementation of an FM modulator and demodulator, using an FM carrier running at 14kHz:
Fantastic. Will try this later. Sadly have to spend the morning debugging software at work rather than having fun with Drambo... 🤨
@rs2000 great experiment. I like the sound. That really reminds me of tuning older transistor FM radios. I did a little mod, added a mixer to add noise and replaced the multiplier with the function module for more experimentation.
Man, this is starting to become fun indeed!
I now added stereo capability just to add that FM feeling to internet radio 😂
Stereo with sub carrier and pilot tone ? - only joking 🙃