Large Ferrite Rod TRANSMiT Antenna for 21Khz on the VLF band - high Q resonant tuned input & output

[Chuck aa0hw]

using a biploar tesla coil with a large ferrite core, 30 windings primary input, and 300 turns secondary output both input and output are tuned for MAX signal output at 21Khz

- input is tuned by a .1uF series resonating CAP, and output is tuned by a .001uF parallel resonating CAP

QRQ CW example for TRANSMIT/RECEIVE

transmitter = RASPBERRY PI 4, using its own analog headphone jack audio output

RECEIVER = laptop sound card SDR, using RECRI KEYER's sdr modules: https://github.com/recri/keyer

[Chuck aa0hw]

Here is an example of a RASPBERRY PI 4 using its own alsa headphone jack to send out 21Khz QRQ CW using FLdigi 

a Gstreamer script provides the CLi APPs & ROUTiNG to send a 21Khz sine wave CW NOTE out of a Raspberry pi's own analog headphone jack the FLdigi CW AUDIO output gets cloned & Re-Created at 21Khz by this Gstreamer script

GSTREAMER SCRIPT USED IN THIS EXAMPLE:

gst-launch-1.0 -v interleave name=i ! audioconvert ! queue ! ladspa-zamgate-ladspa-so-zamgate attack=5 release=5 threshold=-30 sidechain=true ! audioconvert ! audio/x-raw, rate=48000, layout=interleaved, channels=1 ! audiomixer ! audiowsincband mode=band-pass lower-frequency=20900 upper-frequency=21100 length=384 window=3 low-latency=true ! audioconvert ! queue ! alsasink device=hw:3 buffer-time=100000 sync=false async=false audiotestsrc volume=0.31 freq=21000 ! audioconvert ! multiqueue use-interleave=true ! i. alsasrc device=hw:0,1 ! audioresample ! audioconvert ! audio/x-raw, channels=1 ! multiqueue use-interleave=true ! i.

The gstreamer CLi APP that does the CW CLONing, cw regeneration = ZAMGATE FLdigi sends its CW AUDIO output though an alsa-loopback virtual audio cable....the Gstreamer script is listening for any audio on that loopback and directs it to the input sidechain port of ZAMGATE...the gstreamer scripts is holding back a sine wave at 21Khz at the ZAMGATE's pass-through port...

FLdigi basically "keys" ZAMGATE's sidechain port and allows the SINE WAVE to pass through to the next gstreamer module - a 21Khz BANDPASS FILTER and then it connects to the pi's alsa sound card headphone jack and to a CLASS D audio amp and out of the audio amp to the TUNED FERRITE TRANSMIT ANTENNA

Here is an alternative gstreamer script that ADDs monitoring the original FLdigi sidetone on the PI4 RIGHT CHANNEL heapdhone jack stereo output - to class d amp to rt channel speaker - the left channel pi4 headphone jack output would only be for VLF CW output at 21khz: ********************************************************************************************* GST_DEBUG=3 gst-launch-1.0 -v interleave name=i ! audioconvert ! queue ! ladspa-zamgate-ladspa-so-zamgate attack=5 release=5 threshold=-30 sidechain=true ! audioconvert ! queue ! audio/x-raw, rate=48000, layout=interleaved, channels=1 ! queue ! audiorate ! audiowsincband mode=band-pass lower-frequency=20900 upper-frequency=21100 length=384 window=3 low-latency=true ! audio/x-raw, rate=48000, layout=interleaved, channels=1 ! audiopanorama panorama=-1 ! audiomixer name=mix ! queue ! alsasink device=hw:3 buffer-time=50000 sync=false async=false audiotestsrc volume=0.31 freq=21000 ! audioconvert ! multiqueue use-interleave=true ! i. alsasrc device=hw:0,1 ! tee name=t t. ! audioconvert ! multiqueue use-interleave=true ! i. t. ! audioconvert ! audiopanorama panorama=1 ! mix.

HERE IS A VIDEO DEMO of monitoring the FLdigi sidetone that was coded into the gstreamer above: