I previously asked for the tone frequencies and received no answer.
So today I calculated them using this existing email.
Using this email and the quotations:
"at audio tone frequency 750 Hz and 127 polar code symbols at tone
frequencies 750 Hz + n*11.71875 Hz, where n is in the range 1-128"
"the 1512 Hz bandwidth of the SuperFox signal"
"the SuperFox signal (750 Hz - 2262 Hz audio) "
Is "and 127 polar code symbols" a typo?
A bit of arithmetic was used in a spreadsheet.
From the spreadsheet:
----------------------------------
SUPERFOX FREQUENCIES
Stated Bandwidth 1512 750 + 1512 = ~2262
Slot width 11.71875
Beginning of tones 750
End of tones ~2262
Try every n from 0 to 128
n*width Left Edge to Right Edge
0 0 750 to 761.71875
1 11.71875 761.71875 to 773.4375
2 23.4375 773.4375 to 785.15625
...
...
126 1476.5625 2226.5625 to 2238.28125
127 1488.28125 2238.28125 to 2250
128 1500 2250 to 2261.71875 ~2262
Uses n=128 tone slots
and slot 0 i.e. 750 Hz
-----------------------------------------------
On 7/23/2024 12:16 PM, Steven Franke via wsjt-devel wrote:
On Jul 23, 2024, at 10:41 AM, Black Michael via wsjt-devel
<wsjt-devel@lists.sourceforge.net> wrote:
Was looking at this example SuperFox transmission using Audacity
https://www.dropbox.com/scl/fi/stohwy3veidevmwr4j517/240605_181330.wav?rlkey=85h1c9riskq1mmbqzex9hpov3&dl=1
<https://www.dropbox.com/scl/fi/stohwy3veidevmwr4j517/240605_181330.wav?rlkey=85h1c9riskq1mmbqzex9hpov3&dl=1>
It looks like there is amplitude modulation going on which would seem
to be undesirable.
For example, analyzing this one section there is a 1697Hz signal. But
if the amplitude drops the SNR will drop too limiting the decoding
ability.
Is amplitude modulation part of the Q-ary polar code?
The SuperFox audio waveform produced by WSJT-X is a constant-envelope
Gaussian frequency shift keyed (GFSK) signal with bandwidth-time product
BT=8. The GFSK waveform includes 24 sync symbols at audio tone
frequency 750 Hz and 127 polar code symbols at tone frequencies 750 Hz +
n*11.71875 Hz, where n is in the range 1-128.
If the transmitter’s upper-sideband audio-to-RF frequency response is
flat over the bandwidth of the SuperFox signal (750 Hz - 2262 Hz audio)
then the transmitted signal will also have constant envelope. What you
are seeing in the example that you posted is the result of
frequency-selective fading, i.e. the propagation channel’s frequency
response is not flat over the 1512 Hz bandwidth of the SuperFox signal.
Most signals will exhibit this effect so some extent.
Steve K9AN
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