Hi Alexander, LF,
Yes, i assumed the Q of the coil to be very high due to the big wire that is
used in it. But thus the internal C is high, so stray currents occur that
increase the resistive losses. Additionally the proximity effect plays its
role...
Q is low, just abt 38 and thus i get such a low voltage at a given power. But i
will build a own VLF coil soon, with the needed L so that no parallel C will be
required. This may take some days ;-)
The PA gives 130W at 13V now. I will increase the power soon.
Yesterday the wind was suitable and the sun was out :-) So i was on the hill
and did the first test. I even had an oscilloscope there to measure the antenna
voltage and current waveforms. Some photos of the arrangement will be shown on
my site at qrz.com in some days (sri, have forgotten cable between camera and
PC...)
I just had 1,6kVrms on the wire. That is 23dB less than calculated but it was a
first test. So, the ERP was just 1/200. Additionally i have forgotten a part of
the ground radial wich increased the earth resistance. Bernd/DF8ZR received in
a distance of abt 16km but got nothing. But i am not sure if his RX equipment
was really suitable. Ha said he wants to improve it. He also said that he can
receive the Alpha station but as we know from LF: You can excellent receive
DCF39 but get not even the strongest amateur stn if your RX is not optimised...
I received my own TX signal the the soundcard. Signal was 40dB above noise even
without connecting anything to the input and with the PC shielded by the car
housing. That says nothing, i know. Just that there seems to be a high E-Field
in the near or a coupling by the voltage supply... Anyway, i saw that the
signal was clean/stable and "exactly" on the frequency. Trying to receive the
5th harmonic at 45kHz showed no reception in my IC706 (starting at 30kHz :-( )
with a wire connected and the waveform looked perfectly on the scope...
In the next test it may be very useful to have some partable or mobile RX
stations in the region. Markus/DF6NM, what do you think about visiting me
there, or Marco/DD7PC? We could talk and laugh and eat and drink and test and
improve and measure. If we will be not successful we could talk and drink ;-)
That would definitely be the best method to try what is possible with a given
ERP on a given frequency...
It may need some time for the next test but i hope we can keep this VLF fire
burning;-) If Paul receives a signal that is generated by the soundcard, so
with some mW, in 180m, then my optimism is even increasing. But we always have
to be careful with the interpretation of the results and have to ask if it
possible that a galvanic/inductive coupling occured, so no radiation (e.g. by
the power supply cable. Just like the PC QRM can be fed into a sensitive active
E-Field antenna by a galvanic/inductive/capacitive coupling!). So, if the
signal in this example was generated by a battery fed notebook that stood on a
wooden chair in the garden: congrats!! :-)
73 es GL! Stefan/DK7FC
...now searching for a plastic tube with 40...60mm diameter and 1,2m length on
a building lot ;-) Any better ideas?
________________________________
Von: [email protected] im Auftrag von Alexander S. Yurkov
Gesendet: Di 02.03.2010 19:40
An: [email protected]
Betreff: Re: LF: VLF TX experiments_short report
On Mon, 1 Mar 2010, [iso-8859-1] Stefan Sch?fer wrote:
>
> What i wanted to use as the PA is a prototype of a SMPS that was designed to
> operate at abt 50kHz. At 9kHz the ferrite core was already driven in
> saturation. By varying the driving f i found, where the saturation occurs.
> Then i have known how many primary turns i have to spend at 9kHz. After
> applying the new windings everything was right. But the time i had was gone
> and the wind was already to strong. So i told Markus to inform you...
>
> Now playing/increasing with the number of output windings of the SMPS
> transformer i applied the output voltage by a ordinary loudspeaker cable
> to the primary air coil that is inductive coupled to the HV coil. I got
> 1,6kV rms by applying 60W at the 12V DC input, really not much :-( But
> anyway it will be suitable for a first test if a apply 6dB more power or
> so.
Dear Stefan 3.2 kV (6 dB of 1.6 kV) is too low voltage. Expectations was
20 kV before. Is it any typo?
Regards,
Alexander
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