Re: LF: Problem with generator to VLF transmitter

[Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>]

Hi Marcin,

Am 02.12.2012 21:42, schrieb Marcin:

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?

You can generate the 8.97 kHz signal in SpecLab and use a reference signal to compensate the soundcard drift. See the circuit of my first PA to see how the drive stage is made: http://www.iup.uni-heidelberg.de/schaefer_vlf/12V_300W_VLF_PA.pdf
This is easily done and you have most of the circuit already working.

For what do you need to vary the duty cicle from 5...45% ? Is this to adjust the TX power? Or do you want a quasi-linear mode PA? For normal power adjustments i suggest to use simple taps on the secondary winding of the PA output transformer.

An alternative may be DF6NM's outphasing program which he will describe for you :-)

73 and please keep us informed about the progress. There is some growing interest in the 33km band again, also here in DL :-)

73, GL, Stefan/DK7FC

PS: That was a short answer, sri.