| Receiving |
Open WSJT and from the menu select Mode and JT6M or press Shift+Control+F7.
If SpecJT is not open select View/Specjt or F10.
Now click the Monitor button - you are in receive mode. Reference is made here to
Ver.5.x.x WSJT and location in Europe. The following will apply to previous versions except for the differences such as Freeze which is not present on Ver.4
or earlier versions. |
| Make the following initial settings : S = -10, Clip = 0, Tol = 400, Zap, NB and
Freeze all unchecked. |
| The default setting for S is -10. S sets minimum increase in signal that will be accepted as
a ping. Set to -10 will give less "rubbish" decodes than -15 setting but you may not be able to decode weaker pings. Try different values and see the effect when
receiving some JT6M signals. |
| Tol sets the decoder tolerance (in Hz)
to frequency offsets. The default setting is 400 (Hz). This means that signals up to 400Hz from
receive frequency can be decoded. This is the DF value in the WSJT decode area - the DF value shown
in LA1TV screenshot below is -32 - this has produced a very good decode. |
Receive Level
Tune your receiver to 50.230MHz and if you can, set your receiver's AGC to OFF. When receiving, the object is to maintain a "green line" level equal to 0dB ±3dB
on rx with NO signal (JT6M) received. This is indicated on the status bar at the bottom of the WSJT window - RX noise: 0dB. See Freeze DF picture below (Rx noise: 2dB).
Set your receiver's AGC to OFF if this is facility is available. |
| Adjust the sound card input level such that
the Rx noise indicated in the status bar shows 0dB ±3dB. As you
adjust the input level notice the green line on Specjt move up and down as the input level varies.
After a couple of receive periods you should see something similar to the waterfall screenshot
below taken with S = -15. The green line is the receive audio level and the yellow line is the level
of the received sync tone (1076Hz). |
Waterfall area |
When a signal is received (either a ping or burst), a rise of both the green and yellow lines should be seen as
spikes with brighter colours.
The green box at the left below the waterfall shows the time when the mouse is placed over the waterfall, in this case at 20.5 seconds
from the start of the receive period displayed.
The figures to the right show the filename of the saved wav file. Mon_081004_143400 |
| Depending on how noisy your 6M environment is,
you may have to adjust your receiver's AF level and/or the sound cards input level (via Sound
card Audio Mixer) frequently to maintain as near to 0dB RX noise. If Rx noise is shown as in the
screenshot to the right, then the audio input level is very low, audio input is missing or you
are not in Monitor mode. |
Rx noise good |
| Now position your 6M antenna to a direction you may expect to hear some MS JT6M from (check 6M cluster spots to see
if anyone is spotted). The best way is to enlist the help of a known JT6M operator nearby to give you a test signal (preferably not on 50.230MHz) or ask on a chat room
such as ON4KST 4/6M chat. |
Rx noise - no signal |
Decoding
If you hear some pings/bursts, if it is not automatically decoded at the end of the receive
period, you can click in the waterfall area. You will be surprised what can be decoded, even if you
didn't hear anything ! As a bonus you can also click in the SpecJT waterfall area real time to
get instantaneous decodes where spectral indications appear. Running an external spectrograph such
as Spectran can also help identify weak signals that may not show on SpecJT. |
| JT6M attempts to decode both individual pings
and an “average message” based on the entire transmission,
or selected portions thereof. An average message is flagged with an asterisk at the right end of
the decoded text line. Clicking with the left mouse button decodes a 4-second block of data near
the mouse pointer. The right button uses a longer segment of 10 seconds. Drag the mouse with the
button down to select any desired region. Experiment for best decoding as necessary. |
| You will sometimes find that clicking on a smooth
green line, even where nothing was heard and nothing can be seen, causes call signs or other information
to pop up out of the noise. If you decode a call, double clicking on it in the decode area will
insert that call in to the
To radio box and if present in CALL3.txt, will display the Grid, Hot A/B El and AZ values.
Otherwise enter the call manually and click on Lookup. |
LA1TV QSO |
The decoded line in LA1TV QSO screenshot shows
-
093300 11.7 2.4 5 -32 CHE LA1TV G0CHE LA1TV G0CHE LA1TV
File ID : 093300 - time of start of receive period and part of "saved" wav file name, 00 = 1st rx period, 30 = 2nd rx period
T : 11.7 - time of start of decoded burst
Width : 2.4 - length of burst (in secs)
dB : 5 - max. signal level (in dB) above "green line"
DF : -32 - frequency difference (in Hz) from your receive (transmit) frequency (in this
case LA1TV is 32Hz lower) |
| When you receive a signal observe the decoded
signals DF value. The object is to reduce the DF value to as near as
possible to zero and thus reduce the Tol value. DF is the frequency offset that the JT6M decoder
estimates for the required decoded signal to an accuracy of ±
10Hz. How you reduce DF depends on a few factors. If you have not started transmitting in reply to
the signal (probably because you heard a CQ) then use your VFO to retune to reduce DF. If your are
on a sked (scheduled qso) then it is best to use your receivers RIT control. Should your QSO partners
signal be greater than 400Hz then retuning your VFO would be preferred. Large DF values are often found
when operating on 4M, caused by off tune transverters. When in a QSO, retuning the VFO may cause confusion
as your qso partner may have already heard you and made similar adjustments. |
| When the DF value is low, + or - 20hz say, decrease the value of Tol to reduce the probability of
false decoding - a figure of 50 is usual. However be aware that your qso partner's tx may drift and cause the DF value to increase or decrease. |
Freeze DF set to -85Hz |
Freeze
Another method that can be used is Freeze. Check the Freeze box and use the F11 or F12 function keys
to set the Freeze DF value to that of the desired decoded signal. This adjusts the Freeze value
in 5Hz steps. This method is effectively the same as using your receivers RIT control. Having now
reduced DF to near to zero, you should adjust Tol setting to a low value e.g. 100 or 50. This
will improve your decodes. WSJT will then ignore signals where the sync tone is outside the Tol
value. Remember to uncheck and reset Freeze value when starting new QSO. |
Ping Strength
You may also want to set the minimum Ping Strength, 'S', to -12 or more although this will
also give more garbage decodes. However a setting of -15 or more will allow decode of weaker pings/bursts. |
Clip
Clip sets a parameter that establishes the program's immunity to broadband noise pulses. Set Clip to a value greater than 0 if static crashes are
producing too many garbage decodes. |
File Saving
Every time WSJT decodes a signal, whether through auto decode at the end of a receive period
or forced decode due to clicking inside the waterfall display or pressing the decode button, the decoded text is saved to a text file - ALL.TXT. The decoded data is added
to file which over time can grow to a large file size (>1MB+). The ALL.TXT file is date stamped and is useful for reviewing decodes. This file can be erased at any
time via the menu File/Erase ALL TXT. With Ver.4.x.x., this file is called decoded.cum and can be opened with any text editor. To use this file you have to enable it
via menu File/Save Text in File DECODED.CUM. |
| WSJT also allows you to save the received period
in a .wav file format in sub folder RxWav which is created when WSJT is installed. WSJT gives
a number of options : None, Save decoded, Save if Auto On and Save all. These settings are accessed
via the menu Save. You also have the
option to delete these - File/Delete all *WAV files in RxWav. |
Zap
Check the Zap box to filter out birdies (narrowband signals of approximately constant amplitude)
before attempting to decode. |
NB
Check the NB box to blank short noise pulses from the received data before decoding. |
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