Stefan,
Is the TX antenna horizontal? (Like a standard dipole or end-fed?). I wanted to confirm, because a short horizontal antenna in the VLF is an interesting case (in theory, near-field strength similar to a vertical antenna, far-field strength less than a vertical antenna, and field strength at intermediate distances more or less than a vertical antenna depending on exact distance, soil conductivity and other factors). Performance at any distance would be interesting, and especially at distances of 1km or longer.
On another topic, I have some new, stable oscillators, including a very stable oscillator that should support bandwidths less than 50 uHz for 24 hours with or without GPS, over a wide temperature range. I am interfacing two oscillators to SpecLab today (one oscillator for indoor use and the other for portable RX use). After the oscillators are interfaced to SpecLab, I will be able to set up a 2-axis VLF grabber (online), and also do some meaningful VLF TX tests. In the past my VLF TX tests have been limited by oscillator drift in the portable outdoor receiver that I use to measure the TX field at long ranges. Now I should be able to perform TX tests at 50uHz and narrower bandwidths for days at a time, at long distances (I can leave the very-stable GPS-independent oscillator with an RX at remote locations for long periods, regardless of temperature swings, to measure TX field strength).
I’m looking forward to hearing about your tests; 5.7kHz is an interesting frequency from a propagation standpoint, and the antenna performance will be quite interesting.
73, Jim AA5BW
Hi VLF friends,
For those how could be interested in local VLF experiments, i'm now transmitting on the 70m long 30m high antenna with the LOPT transformer. TX power is just 3W. Mode is QRSS-400. The transmit frequency is 5.756666 kHz, GPS "locked" in SpecLab.
Last night i've done a first local test on that frequency, 30m distance. The signal was visible in the grabber window, as well as a weak 3rd harmonic was detected (3HD) at 17.27 kHz.
Now, with the todays experiment i'm trying to receive that weak signal on 5.75666 kHz from my home QTH in nearly 1 km distance. If successful, a few /p receive tests will be done. And, in previous tests, "the big coil" will be used.
73 and gl with your own projects :-)
Stefan/DK7FC
