Hi Stefan,
...But thus the internal C is high, so stray currents occur that increase the resistive
losses. Additionally the >proximity effect plays its role...
Do you mean circulating currents by 'stray currents' ?
Did you measure the self resonant frequency of your coil?
As long as you operate at half its self resonant frequency stray capacitance
won't hurt
regarding losses.
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.
Doubling a given inductance by a parallel C will quadruple losses at the same
frequency.
73
Clemens
DL4RAJ
----- Original Message -----
From: "Stefan Schäfer" <[email protected]>
To: <[email protected]>
Sent: Tuesday, March 02, 2010 9:09 PM
Subject: AW: LF: VLF TX experiments_short report
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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