Hi Jim,
Am 30.01.2014 19:08, schrieb hvanesce:
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).
The antenna is an inv-L, strung between 2 buildings, like the recent
shown lightning strike image. I guess it acts as a pure vertical
antenna with capacitive top load.
Performance
at any distance would be interesting, and especially at distances of
1km or longer.
Last evening i detected the signal in 950m distance. The SNR of
the 5.76666 kHz signal was 45 dB in 4.5 mHz FFT BW which is surprising
good because i do not have a clean earth for the RX antenna which was a
short active E field antenna fixed outside the window of the house.
Coincidentally i even discovered a very weak trace on 17.27 kHz, 3HD
;-) That signal was 40 dB above the noise in the same BW, probably due
to the much lower QRN and QRM and due to the receivers frequency
response. The SpecLab sessions were "locked" to DHO-38 on 23.4 kHz.
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.
I'm looking forward to your grabber and especially to your VLF tests!
As you can see, the first kms can be done with a minimum of effort!
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).
Very well. If you have some nearby interested OMs doing tests on VLF
with you, maybe in 10km distance or so, you can be happy. I want to ask
my working colleague to set up a prearranged temporary VLF grabber in
about 10km distance :-)
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.
Hope these results were motivating for your own tests :-)
73, GL, Stefan/DK7FC
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
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