Hi VLF,
It's time to come back to 5.17 kHz where i have been in the last kite
experiments 2010/2011. The best result was about 10 dB in 3.8 mHz in 904
km distance, detected by SQ5BPF. His website about this experiment is
still on the web,
http://www.lipkowski.org/~sq5bpf/dk7fc_20101023/index_en.html
In these kite tests my ERP was about 3 mW on 5170 Hz. But this was with
a 300m vertical antenna!
With my fixed antenna i can never radiate such strong signals. The
limiting factor is the coil which can handle 250 mA on that frequency.
The radiation resistance is about 210 uOhm, so the ERP will be up to 23
uW. So this is 20 dB weaker (oh, actually i expected it is even more
weaker). But on the fixed antenna it is no problem to transmit 100x longer!!
We will see what is possible on that band with such a low power. Who
wants to make a guess? :-)
But i'm not yet sure if i can resonate the antenna down there at all.
The plan is to use the small coil that was used for 6470 Hz. Inside the
coil there are 100 iron powder cores, shown here
https://dl.dropboxusercontent.com/u/19882028/VLF/20160415_155753.jpg and
here
https://dl.dropboxusercontent.com/u/19882028/VLF/20160415_163021.jpg I
want to replace (a few) of them by ferrite cores, many ferrite cores
"switched in parallel". I need to get the inductance down from 1.2 H to
2.0 H. So first the ferrite cores much provide a higher effective µr
(ur) which is no problem i guess. Secondly the must not saturate (to
much), which is the critical question here. We will see what happens...
It's the right time in the year for such a work and i think i can do a
first transmission on 58 km during this week...
73, Stefan
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