Alexanderson day

[roadster]

For anyone who has acces to a receiver which will tune down to 17.5kHz, the 5th July is the annual opportunity to hear the Alexanderson alternator transmitter in operation. For those not fortunate enough, there are links from the link below to a live  youtube channel.

https://alexander.n.se/alexanderson-day-2020/?lang=en

[ppppenguin]

The Alexanderson Alternator was one of those mad inventions that worked. We are indeed fortunate that one (and only one) has survived and is in working order. Before we had valves the Alexanderson Alternator and the Poulsen Arc were the only ways of generating continuous wave RF.

[Mike Watterson]

A receiver can easily be made with a dual op-amp band pass filter. Then just add diode detector or SAA612 up mixer.
You'd want at least a 1m loop with about 400 turns of any wire. Or a very long aerial. Can do duty as Atmospherics receiver afterwards.

[Refugee]

I have for several years wondered if the degaus coil from a large CRT telly would work.
It is not the day for it this year due to family matters.

[Amie]

Hi all.

Starved Twin T oscillator and use the signal to trigger. Loop aerial with inductance transformation tuning, wouldn't want to wind that torriod by hand though.

Thanks.
Amie

[Doodlebug]

    Here it is...…..
I shall be tuned in on my AOR 7030

[BusyBee]

Maybe, in theory, my Yaesu can but I suspect my limited aerials would preclude this. The lowest I have received were the 50kHz Rugby (obviously some while ago) but have never tried lower. If I remember I will try.

Tracy

[Mike Watterson]

You don't need a receiver for less than 48 kHz, certainly not for less than 24 kHz. Just a band pass amplifier and plug it into sound card sampling at 48 kHz or 96 kHz. Plenty of free software on Android (use 4 pole plug to use the mic in connection on a phone/tablet), Windows and Linux.
Search for VLF or Whistlers. Many of the circuits are old. You can use an LM358 opamp. There is not really any advantage in using a lower noise part unless you have a big loop aerial. Either have a filter specifically for Alexanderson or a good 22 kHz low pass and 12 kHz high pass. If you can do 96 KHz sampling then you can have a higher low pass. It must be a bit less than 1/2 the sample rate as filters are not cliff edge. You might want 2 x LM358 for four stages of filter. Even my Android Tablet does a quite good waterfall spectrum display.
You can use Cat5 cable with the pairs shorted to give four wires. Then connect the "loops" in series to give x4 turns per loop. Around a window frame or three shelves of a bookcase with as many turns as there is wire. You can use twin bell wire and then connect the two wires in series. Or 4 core alarm wire. Treat any twisted pair as one wire, shorting both ends. Shielded Cat 5 may work with the shield earthed at only one end.
It's not critical.
You can calculate or measure the inductance and "resonate" it with a capacitor which might 10nF to 100nF depending on the number of turns.

There is also ELF. Same techniques but below 50 Hz using spikes in the ground.

[Doodlebug]

You can use Cat5 cable with the pairs shorted to give four wires. Then connect the "loops" in series to give x4 turns per loop. Around a window frame or three shelves of a bookcase with as many turns as there is wire. You can use twin bell wire and then connect the two wires in series. Or 4 core alarm wire. Treat any twisted pair as one wire, shorting both ends.  Shielded Cat 5 may work with the shield earthed at only one end.
It's not critical.

Here's my old existing loop using 4 core alarm cable.

   

[Panrock]

Has VLF ever been modulated by audio*? In this case, maybe a 'magnetic amplifier' could be used? Obviously, the sidebands would be appreciable.

Can VLF ever be radiated efficiently by means other than a very long wire?

Questions!

Steve

*Worth trying with NBTV too!