Hello Steinar,
My antenna is a 70m long and 30m high inv-L antenna. The coil is on the
roof, i.e. on the top of the building, see picture in my last mail.
>From my last VLF experiments i built a coil that was designed to
resonate a 100m vertical antenna on 8970 Hz, i.e. it has about 550 mH
with a variometer part of arround 30 mH. DC losses of that coil is
about 320 Ohm, so most of the power ( > 90 %) is lost in the coil.
The antenna wire is hold on the building with ceramic isolators what
can withstand 36 kV rms in rain/snow/ice/dirt, so if its reasonable dry
and clean i estimate it will withstand 100 kV rms without a problem.
But the coil is critical! It was quite a lot of work to wind it as you
can imagine, so i decided to limit the voltage across the coil to 50 kV
rms.
My fixed antenna has about 100 pF less than the 100m kite vertical,
this is why i have to add the external plate capacitor...
I just got 780 mA at 350 W, so the loss resistance is 575 Ohm. As you
can see the coil is standing on the bottom of that building so there
may be significant losses of the magnetic field in the roof/bottom. But
as long as the voltage is the limiting factor i do not care about
losses since nothing is won if i reduce the losses. The ERP stays
constant then...
The TX frequency is generated in my PC, using SpecLab as the frequency
generator, locking to a 10 kHz reference signal coming from my GPS
module. Signal is fed through a fiber optic cable to prevent any EMC
problems....
The signal is still running without any interruptions. There seemed to
be a phase glitch arround 17:15 UTC but since that time the frequency
seems to be pretty clear. My "DFCW-60" grabber window is a good
indicator to check that:
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html
BTW i'm using a different GPS module for the TX notebook, the grabber
runs its own module. So if a phase glitch becomes visible there, it
could also come from my RX (i.e. the VLF grabber PC).
73, Stefan/DK7FC
Am 26.11.2011 19:14, schrieb Steinar Aanesland:
Stefan
You have probably mention this some place, but please repeat it me,
what kind of antenna are you using now ?
la5vna S
Den 26.11.2011 18:16, skrev Stefan Schäfer:
VLF,
Am 26.11.2011 17:55, schrieb Markus Vester:
Once more, Paul Nicholson is showing a good trace:
Wow, yes, very good!
Well, the system runs on the GPS locked system now since 17:00 UTC and
i'm running 780 mA on 8970.00000 Hz. Will go for dinner now and leave
the system running some hours. The WX looks quite useful, no rain, poor
wind and no fog! Maybe i will even run it overnight until tomorrow,
transmitting a streight carrier at 350 W RF. Can't do more
unfortunately, due to the cola-cap ;-)
Now as the signal is locked and non-drifting there may come up
something on the 6000-windows...
Maybe Paul or others can do some calculations, estimating the ERP? I
think it should be in the range of 200 uW. Up to 6 dB can be added in
further tests, i hope.
Markus, a S/N (better S and N ;-) ) plot on your side would be
interesting. My ERP should be constant now so we can observe the QSB,
caused by propagation...
A photo of the todays arrangement: http://dl.dropbox.com/u/19882028/VLF/DSC04268.JPG
73, GL, Stefan/DK7FC
... well done!
Markus
Sent: Saturday, November 26, 2011 4:33 PM
Subject: Re: VLF: 8970 Hz transmissions, soon again
here
Stefan,
around 15:00, your sig on 8970.008 was visible in
Nuernberg, peaking ~ 20 dB SNR in 0.48 mHz.
Viel Glück,
Markus (DF6NM)
Sent: Saturday, November 26, 2011 3:57 PM
Subject: Re: VLF: 8970 Hz transmissions, soon again
here
VLF,
I'm now running 350W into the system and get about 0.8 A antenna
current. Strong audible partial discharges occurr on a parallel fixed
plate capacitor, spaced by 3 cola bottles (0.33l ;-) ). At 550 mH i
have
25 kV rms on the antenna and coil which seems to be no problem at all.
The frequency is still a bit unstable since i took the DDS VFO which is
more comfortable to find the resonance. I will now try to slightly QRO
and then apply a fiber optic cable carrying the GPS locked frequency
coming from the PC/SpecLab, hopefully without to many phase glitches.
Currently i may have an offset of some 20...30 mHz and a slight drift
but it is a first successfully test :-)
73, Stefan/DK7FC
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