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Marcin,
happy to read about upcoming Dreamers band
activity! Just a few comments:
- 70 mH inductance seems too small for
the antenna capacitance. Using capacitors (4 nF) in parallel to the
antenna is unfortunately very inefficient, as only a small part
of the coil current will go to the antenna. This would decrease the
effective coil Q by a large factor (Cant+Cp)/8, ie about 8. It would
be better to use more turns of thinner wire to bring the inductance
up.
- according to the photo, the IGBT module seems to
be wired as a half-bridge, with the transistors internally connected
in series at C2E1. You would have to break up that connection to use
them in grounded emitter push-pull configuration.
- do you want to change the duty cycle to modulate
the output power? With both transistors off, the current will have to go through
the freewheeling diodes, which will probably have unwanted effects on
the voltage waveforms.
- SpecLab with samplerate correction is probably
the easiest choice for an 8.97 kHz sinusoidal signal generator. But with
some PC's there can be problems with sampling gaps or glitches on the
output. In my opinion, an optimal hardware solution is a programmable
Rubidium synthesizer, followed by a fixed divider eg /1024. Chinese second-hand
FE5680-A modules are available around 80 Euro on eBay.
- Stefan mentioned linear AM by outphasing. For
this you would need two half bridges with two independent drivers, which can be
driven by two channels from a stereo soundcard.
Wishing the best of luck,
73, Markus (DF6NM)
Sent: Sunday, December 02, 2012 9:42 PM
Subject: LF: Problem with generator to VLF
transmitter
Hi All!
We’re building an 8,970kHz VLF transmitter at SP2KDS club.
We almost have everything in place:
What we still need is a generator to feed the transmitter. Required
parameters are the following:
- 8,970kHz frequency
- regulating range +-0.05Hz
- adjusting duty cycle of 5 to 45%, at 5% for two
signals at the same time
- two signals shifted by 180 degrees
A friend of mine has promised to build it but it’s been over a year now and
nothing has happened.
Is there a software which would use a soundcard with the aforementioned
parameters?
73! Marcin SQ2BXI
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