Low cost earth-mode beacons?

G1KQH has found some very low cost TDA2003 ICs.  I use one of these in my VLF beacon shown in my RSGB RadCom article and on my website. Best range is just short of 6km by "utilities assisted" earth-mode.  When fitter again (currently I am not allowed to drive and I am still too clumsy when on my feet and moving because of my brain bleed last year) I intend to continue my VLF experiments. I have used these ICs at 8.97kHz, twice, and sub-multiples of that frequency.  Beyond 20kHz would be outside their spec limits, but they may still work?

G3XBM 5W VLFearth-mode CW/QRSS beacon

Evening Roger,

Used in your LF PA 10p each nuts!

http://www.banggood.com/100pcs-TDA2003-10W-IC-Car-Radio-Audio-Amplifier-Integrated-Circuit-p-944202.html

Or you can buy in 10s @ 16p each inc delivery!

http://www.banggood.com/10pcs-TDA2003-10W-IC-Car-Radio-Audio-Amplifier-Integrated-Circuit-p-922620.html

Banggood sounds Chinese. I have no idea if these are genuine parts or not. They are advertised as 10W car radio audio parts.

4W TX for sub-9kHz experiments

Attached is a picture of the "transmitter" I'm using for my ground and induction communications tests. It uses a TDA2003 audio IC into a toroidal step-up transformer that can match from 10 to 150 ohms. Not sure of the transformer type which came from an old Pye Telecom PMR radio, possibly an M206, Whitehall or similar (it was used on the audio stages). I haven't yet tried listening with an active probe antenna to see how that would perform. Time is limited, so further tests may have to wait until the end of the month. Best range so far, receiving "by ear" on a loop antenna, with no clever selectivity or signal processing, is 0.35km.