mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-11-29 07:39:43 -05:00
61 lines
3.3 KiB
Plaintext
61 lines
3.3 KiB
Plaintext
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
|
|
LF and MF bands. T/R periods from 15 s up to 1800 s are
|
|
available. Longer T/R periods provide better sensitivity only if
|
|
Tx and Rx frequency instability and channel Doppler spread
|
|
are small enough so that received signals
|
|
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
|
|
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 1800 s T/R period is 0.089 Baud, so
|
|
successful operation using this T/R length requires Tx and Rx frequency
|
|
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.
|
|
|
|
Operation with FST4 is similar to that with other _WSJT-X_ modes: most
|
|
on-screen controls, auto-sequencing, and other features behave in
|
|
familiar ways. However, operating conventions on the 2200 and 630 m
|
|
bands have made some additional user controls desirable. Spin boxes
|
|
labeled *F Low* and *F High* set lower and upper frequency limits used
|
|
by the FST4 decoder, and these limits are marked by dark green
|
|
angle-bracket symbols *< >* on the Wide Graph frequency scale:
|
|
|
|
image::FST4_Decoding_Limits.png[align="center"]
|
|
|
|
{empty} +
|
|
|
|
image::FST4_center.png[align="center"]
|
|
|
|
It's best to keep the decoding range fairly small, since QRM and
|
|
transmissions in other modes or sequence lengths will slow down the
|
|
decoding process (and of course will be undecodable). By checking
|
|
*Single decode* on the *File | Settings | General* tab, you can
|
|
further limit the decoding range to the setting of *F Tol* on
|
|
either side of *Rx Freq*.
|
|
|
|
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*.
|
|
- 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
|
|
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.
|
|
- 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
|
|
...\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"]
|