Hello Bill, VLF
Am 31.01.2012 04:42, schrieb Bill de Carle:
I
wanted to duplicate what Stefan did using the GUI version: generate a
signal on 8970 Hz using 24000 s/s. It *seemed* to work OK but when I
examined the sound card output signal with Cool Edit, the frequency was
way low - about 8241 Hz instead of 8970.
Yesterday i noticed the same while i was running a SL window to the
same time to check the S/N.
A first RF test using WOLF on VLF was successful too. My ODX is 0.3 m
;-) I just checked if the VLF E probe works. The RF signal came from a
simple 50cm piece of wire connected to the soundcard output.
So I went back to the original command line programs. I found that
versions 0.51 and 0.61 apparently worked, generating 2,304,000 audio
samples (exactly 96 seconds at 24000 s/s) to a file called WOLFX.WAV.
Unfortunately the samplerate in the .wav file header was coded as 8000
s/s, which means if we played it back it would run for 288 seconds and
the audio carrier frequency would appear at 2990 Hz. So I went in and
manually changed the s/s field in the wav header to 24000 s/s. Then
the file worked OK. I was able to decode the message by mixing the
8970 Hz down to 800 Hz and decimating the sample rate to 8000 s/s.
Turning again to the GUI version, I asked it to encode a .wav file at
24000 s/s with a carrier freq of 8970 Hz. It reported version 0.62 and
everything OK. However, when I examined the WOLFX.WAV file so created,
its .wav header said the samplerate was 22050 s/s instead of 24000
s/s! That explains why the real-time GUI uutput seemed low in
frequency: 8970 * 22050 / 24000 = 8241.1875 Hz. The upshot is we need
to manually check the wav header and set the s/s field to 24000 instead
of whatever else it might say. And furthermore, don't trust the
real-time Tx soundcard output signal frequency with the GUI version,
especially when using odd-ball sample rates and high output frequencies
which may never have been tested.
OK, so i will do some tests with different sample rates. I think it
should be no problem to run it at 22050 S/s.
When the keying with an
Be aware that WOLF generates envelope-shaped audio, so it might be more
difficult to convert it to a clean square wave to drive a Tx,
especially near the phase transitions where the amplitude drops down to
zero.
I will see soon. Noticed that the FETs (2x IRFP064N) of my VLF 300W PA
were blown up. Cant't remember when that happend. Will repair that and
then do first local tests, again with a short piece of wire but a
higher output voltage. So i may cover 3m distance ;-)
Also i already switched a CD4070 XOR gate between the outputs of the
CD4013 which drives the ICL7667 to switch the FETs in this PA. BTW this
is the PA is used in my first VLF experiments (1...4th or so). But i
saw that it is not so easy to get the toggle signal from the RS232,
that was a miss up :-/ Then i actually read the manual a bit and found:
WOLF - a proposed new signal format for LF weak-signal work
Driving an "XOR gate" PSK transmitter
Starting with version 0.31, WOLF provides
three ways to drive a transmitter which has a logic input to control
the carrier phase. One method writes a wolfx.wav file which has a tone
present for ones and absent for zeros. You rectify the audio output,
filter it with a time constant of about a milliseconds, and use the
result to key your Tx. For instance:
C:\wolf>wolf -x "QUICK BROWN FOX" -k -e -r 8000.123 -f 3000
WOLF version 0.31
Wrote wolfx.wav, 768056 bytes, at 8000.125 samples/sec., 3000.000 Hz
With this "keyed" output format, selected
with the 'k' option, an output frequency of 3000 Hz was chosen to make
filtering easier. You can also adjust for sound card sampling rate
error, if needed.
...but personally i don't want to spend any time with these DOS
commands stuff / world. That is displeasing for me.
So the question is if i can use the WOLF gui program to get what i
want? Some things can be changed in the config file but don't know how
i can get the RS232 to generate the toggle signal for the phase shift
:-/
I'll focus on some local tests with the LOPT and build the PA drive
comparator circuit...
73, Stefan/DK7FC
73,
Bill VE2IQ
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