Hi Bill and Jim,
Thanks for making some things clear. I didn't spend to much attention to
that mode so far. I won't use it on LF (ockay, never say never) but on
VLF it may be interesting for me. The reason is, as recently explained,
that stations can wait until a decode appears. If the signal level is
strong (due to low distance and/or a nice RX location), a first decode
appears after a short while and if its weaker, it takes a bit longer ;-)
...as if the bandwidth of a QRSS window becomes smaller and smaller with
time, instead of scrolling. Not so easy to explain at 2:30 AM ;-)
OK about the BW limiting issue. I think on VLF this is really no problem.
Am 30.01.2012 01:37, schrieb Bill de Carle:
With your Q=1000 coil it might be possible to de-Q it keep the
sidebands reasonable[...]
Well, on 8970 Hz my (loaded) antenna Q is 45. So the mentioned 40 Hz
bandwidth is no problem. The loaded Q of the 300m kite antenna on 8970
Hz is even just 30!
Can your Tx handle abrupt phase shifts every 100 msec?
Yes.
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?
With a XOR gate or so this can be done externally i think. Yes, i
squeezed it to generate DFCW from an external command so it will
generate WOLF as well. That would have the advantage to prevent phase
glitches that come from soundcards sometimes. And the drift+offset would
be low enough (< 50 mHz).
But that sounds to complex. Let me think a bit about it and do some
first trials. I've not even downloaded the software, just a first thought.
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.
Or a CD4013, yes, like i do on VLF all the time.
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.
I think the phase keying will be no problem for the PA. At least we can
simply test it. On VLF i'm running just a few 100W so i don't expect any
problems.
73, GN, Stefan/DK7FC
73,
Bill VE2IQ
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