At 06:47 PM 1/29/2012, Stefan DK7FC wrote:
Hmmmmmmmmmmmm, so what about a WOLF VLF test? Can the program easily
be configured to transmit at 8970 Hz? I.e. does it generate a tone
at that frequency? Please confirm that no linear mode PA is needed.
Wolf 10, means 10 Hz bandwidth? Sorry for the basic questions, i
could read the manual but its like reading readme files ;-)
Starting with local tests should show the limits and chances.
DD7PC who is in 77 km to my fixed location gave a WOLF report today,
so maybe...
And if OK2BVG can reveive my DFCW-3 from the 300m kite, it may be
worth to spend some time for a WOLF.
I could ask Michael Oexner first. He is just 45 km distant...
Well, it doesn't require a linear PA as long as you can sufficiently
attenuate excessive sidebands by other means - it *is* BPSK so
inherently quite wide (the power spectrum falls off only as the
inverse square of frequency). Bandwidth-friendly versions shape the
waveform to reduce those pesky sidebands, and that would require a
linear PA, but I could send you a .wav file for 8970 Hz with a true
(unshaped) BPSK WOLF-coded test message in it - all you'd have to do
is play it in a loop. With your Q=1000 coil it might be possible to
de-Q it keep the sidebands reasonable while still allowing the
envelope to recover back to full amplitude within say 50 milliseconds
after each phase shift. Can your Tx handle abrupt phase shifts every
100 msec? We can arrange for the phase shifts to occur only at
zero-crossings of the 8970-Hz sinewave. Wolf 10 means sending 10
bits per second, i.e. the minimum time between 180-degree carrier
phase shifts is 100 msec. It might be easier to generate it with a
DDS instead of a sound card. Can your DDS do a 180-degree phase
shift on external command? If not we can make a DDS that will
generate a WOLF signal at 8970 Hz. One neat way to do it would be to
start with a squarewave at 17940 Hz then divide it by 2 with a 74HC74
flop. A microprocessor counts the clocks and gates out one toggle
pulse whenever a 180-degree phase shift is required, resulting in the
desired squarewave carrier waveform at 8970 to drive your Tx.
73,
Bill VE2IQ
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