LF: Software-based VLF Receiver

[DL4YHF@aol.com]

Hello group,

Because of the coming test transmissions on 16kHz and 17.2kHz, I did a few 
tests with 'direct reception' of LF signals up to 20 kHz using only the PC, a 
soundcard, a piece of software and a few metres of wire. The results are 
good, and may be useful for some of you. 

The basic concept:
- soundcard running at 44100 Hz sample rate
- input signal is converted to 650Hz audio with an image-rejecting mixer
  (phase method, using a Hilbert transformer)
- output from the mixer (650Hz) filtered with IIR or FIR filter,
 100Hz bandwidth or less
- output from the filter passed to soundcard output (in real-time).


You need a PC with at least 166MHz, Spectrum Lab V1.65 beta5 (new).

The problem is that not all soundcards are suited for this "full duplex" 
operation (or, to be precise, the control program does not allow the proper 
settings). I did a few tests on some PC's, on two it worked immediately and 
one (a notebook) had kind of a 'feedback' problem.


More info can be found here:
  http://www.qsl.net/dl4yhf/vlf_rcvr.html  .

The 'special pre-release' of Spectrum Lab V1.65 beta5 can be loaded from:
  http://members.aol.com/dl4yhfhamsoft/spectr_i.zip

I am very interested in the 16kHz transmission from GBR, hope it's going to 
work. Thanks for passing the info about GBR, Mike. 

User feedback welcome. Good luck, cu on 136kHz,
   73's Wolf (DL4YHF, DF0WD).