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Add discussion of noise blanker in FST4 section of docs.

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Steven Franke 2021-02-19 09:16:27 -06:00
parent b194cc1a14
commit 954cf00b6c
2 changed files with 25 additions and 11 deletions
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35
doc/user_guide/en/tutorial-example5.adoc
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@ -1,15 +1,17 @@
Do not confuse FST4 with FT4, which has a very different purpose! Do not confuse FST4 with FT4, which has a very different purpose!
FST4 is designed primarily for making weak-signal 2-way QSOs on the FST4 is designed primarily for making weak-signal 2-way QSOs on the
LF and MF bands. T/R periods from 15s up to 1800s are LF and MF bands. T/R periods from 15 s up to 1800 s are
available. Longer T/R periods provide better sensitivity provided that the available. Longer T/R periods provide better sensitivity only if
combined effects of Tx and Rx frequency instability and channel Doppler spread Tx and Rx frequency instability and channel Doppler spread
yield a received signal that remains coherent over the duration of are small enough so that received signals
several transmitted symbols. Generally speaking, Rx and Tx frequency changes remain phase coherent over periods spanning several transmitted symbols.
Generally speaking, Rx and Tx frequency changes
during the transmission and channel Doppler spread should each be small compared during the transmission and channel Doppler spread should each be small compared
to the symbol keying rate shown for each T/R duration in Table 7 within section to the symbol keying rate shown for each T/R duration in Table 7 within section
<<PROTOCOL_OVERVIEW,Protocol Specifications>>. For example, the keying rate for the 1800s T/R period is 0.089 Baud, so <<PROTOCOL_OVERVIEW,Protocol Specifications>>. For example, the keying rate for
the 1800 s T/R period is 0.089 Baud, so
successful operation using this T/R length requires Tx and Rx frequency successful operation using this T/R length requires Tx and Rx frequency
stability better than 0.089 Hz over the duration of the 1800s transmission in stability better than 0.089 Hz over the duration of the 1800 s transmission in
addition to channel Doppler spread smaller than 0.089 Hz. addition to channel Doppler spread smaller than 0.089 Hz.
Operation with FST4 is similar to that with other _WSJT-X_ modes: most Operation with FST4 is similar to that with other _WSJT-X_ modes: most
@ -33,15 +35,26 @@ decoding process (and of course will be undecodable). By checking
further limit the decoding range to the setting of *F Tol* on further limit the decoding range to the setting of *F Tol* on
either side of *Rx Freq*. either side of *Rx Freq*.
.Open a Wave File: A noise blanker can be enabled by setting the *NB* percentage to a non-zero value.
This setting determines how many of the largest-amplitude samples will be
blanked (zeroed) before the data is submitted to the decoder. Most users find
that settings between 0% (no blanking) and 10% work best. If the noise
blanker percentage is set to -1%, then the decoder will try 0, 5, 10, 15, and 20 %
in succession. Similarly, a setting of -2% causes the decoder to loop over
blanking percentages 0, 2, 4, ... 20 %. To save time, the multiple blanking
percentages triggered by negative *NB* settings are tried only for signal
candidates located near (within +/- 20 Hz) of the *Rx* frequency setting.
.Open a sample Wave File:
- Select *FST4* on the *Mode* menu. Set *T/R* to 60 s and *Decode | Deep*. - Select *FST4* on the *Mode* menu. Set *T/R* to 60 s and *Decode | Deep*.
- Set up the Wide Graph display so that it has settings appropriate for the FST4-60 mode. - Set *NB* (noise blanker) to 0%.
- Set up the Wide Graph display with settings appropriate for the FST4-60 mode.
For example, try *Bins/Pixel* 2 and *N Avg* 4. Set the *Start* frequency and the width of For example, try *Bins/Pixel* 2 and *N Avg* 4. Set the *Start* frequency and the width of
the Wide Graph to cover the entire frequency range that you want to decode. For this the Wide Graph to include the frequency range that you want to decode. For this
example, make sure that *Start* is less than 1000 Hz and that the Wide Graph extends to above 1400 Hz. example, make sure that *Start* is less than 1000 Hz and that the Wide Graph extends to above 1400 Hz.
- Set *F Low* 1000, *F High* 1400. These settings define the decoder's frequency search range. - Set *F Low* 1000, *F High* 1400. These settings define the decoder's frequency search range.
- Open a sample Wave file using *File | Open* and select the file - Open a sample Wave file using *File | Open* and select the file
...\save\samples\FST4+FST4W\210115_0058.wav. When the file opens you should see something similar to the following screen shot: ...\save\samples\FST4+FST4W\210115_0058.wav. After _WSJT-X_ has processed the file you should see something similar to the following screen shot:
image::FST4-1.png[align="left"] image::FST4-1.png[align="left"]

1
doc/user_guide/en/tutorial-example6.adoc
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@ -20,6 +20,7 @@ scheduling behavior, you should select *Random* with this control.
.Open a Wave File: .Open a Wave File:
- Select *FST4W* on the *Mode* menu. Set *T/R* to 1800 s and *Decode | Deep*. - Select *FST4W* on the *Mode* menu. Set *T/R* to 1800 s and *Decode | Deep*.
- Set *NB* to 0%.
- Select appropriate wide graph settings. For example, try *Bins/Pixel* 1, - Select appropriate wide graph settings. For example, try *Bins/Pixel* 1,
*Start* 1200 Hz and *N Avg* 150. *Start* 1200 Hz and *N Avg* 150.
- Open a sample Wave file using *File | Open* and select the file - Open a sample Wave file using *File | Open* and select the file