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442 lines
18 KiB
Plaintext
442 lines
18 KiB
Plaintext
_WSJT-X_ supports a number of features designed for use on the VHF and
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higher bands. These features include:
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- *FT4*, designed especially for contesting
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- *FT8*, designed for making fast QSOs with weak, fading signals
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- *JT4*, particularly useful for EME on the microwave bands
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- *JT9 fast modes*, useful for scatter propagation on VHF bands
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- *JT65*, widely used for EME on VHF and higher bands
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- *QRA64*, another mode for EME
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- *MSK144*, for meteor scatter
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- *ISCAT*, for aircraft scatter and other types of scatter propagation
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- *Echo* mode, for detecting and measuring your own lunar echoes
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- *Doppler tracking*, which becomes increasingly important for EME
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on bands above 1.2 GHz.
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[[VHF_SETUP]]
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=== VHF Setup
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To activate the VHF-and-up features:
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- On the *Settings | General* tab check *Enable VHF/UHF/Microwave
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features* and *Single decode*.
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- For EME, check *Decode after EME delay* to allow for extra path
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delay on received signals.
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- If you will use automatic Doppler tracking and your radio accepts
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frequency-setting commands while transmitting, check *Allow Tx
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frequency changes while transmitting*. Transceivers known to permit
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such changes include the IC-735, IC-756 Pro II, IC-910-H, FT-847,
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TS-590S, TS-590SG, TS-2000 (with Rev 9 or later firmware upgrade),
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Flex 1500 and 5000, HPSDR, Anan-10, Anan-100, and KX3. To gain full
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benefit of Doppler tracking your radio should allow frequency changes
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under CAT control in 1 Hz steps.
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NOTE: If your radio does not accept commands to change frequency
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while transmitting, Doppler tracking will be approximated with a
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single Tx frequency adjustment before a transmission starts, using a
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value computed for the middle of the Tx period.
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- On the *Radio* tab select *Split Operation* (use either *Rig* or
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*Fake It*; you may need to experiment with both options to find one
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that works best with your radio).
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- On the right side of the main window select *Tab 1* to present the
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traditional format for entering and choosing Tx messages.
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The main window will reconfigure itself as necessary to display
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controls supporting the features of each mode.
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- If you are using transverters, set appropriate frequency offsets on
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the *Settings | Frequencies* tab. Offset is defined as (transceiver
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dial reading) minus (on-the-air frequency). For example, when using a
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144 MHz radio at 10368 MHz, *Offset (MHz)* = (144 - 10368) =
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-10224.000. If the band is already in the table, you can edit the
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offset by double clicking on the offset field itself. Otherwise a new
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band can be added by right clicking in the table and selecting
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*Insert*.
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image::Add_station_info.png[align="center",alt="Station information"]
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- On the *View* menu, select *Astronomical data* to display a window
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with important information for tracking the Moon and performing
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automatic Doppler control. The right-hand portion of the window
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becomes visible when you check *Doppler tracking*.
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image::Astronomical_data.png[align="center",alt="Astronomical data"]
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Five different types of Doppler tracking are provided:
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- Select *Full Doppler to DX Grid* if you know your QSO partner's locator
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and he/she will not be using any Doppler control.
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- Select *Own Echo* to enable EME Doppler tracking of your receive
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frequency to your own echo frequency. Your Tx frequency will remain fixed
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and is set to the Sked frequency. This mode can be used when announcing
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your CQ call on a specific frequency and listening on your own echo
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frequency. It can also be used for echo testing with Echo mode.
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- Select *Constant frequency on Moon* to correct for your own one-way
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Doppler shift to or from the Moon. If your QSO partner does the same
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thing, both stations will have the required Doppler compensation.
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Moreover, anyone else using this option will hear both of you
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without the need for manual frequency changes.
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- Select *On Dx Echo* when your QSO partner is not using automated
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Doppler tracking, and announces his/her transmit frequency and listening
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on their own echo frequency. When clicked, this Doppler method will
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set your rig frequency on receive to correct for the mutual Doppler
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shift. On transmit, your rig frequency will be set so that your
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QSO partner will receive you on the same frequency as their own echo
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at the start of the QSO. As the QSO proceeds, your QSO partner will
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receive you on this starting frequency so that they do not have to
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retune their receiver as the Doppler changes. Sked frequency in this
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case is set to that announced by your QSO partner.
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- Select *Call DX* after tuning the radio manually to find a station,
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with the Doppler mode initially set to *None*. You may be tuning the band
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looking for random stations, or to a frequency where a station has been
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seen on an SDR display. It is usually necessary to hold down the Ctrl key
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while tuning the radio. From the moment *Call DX* is pressed, your
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transmit frequency is set so that your echo will fall on the same
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frequency you (and the DX station) are listening.
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- See <<ASTRODATA,Astronomical Data>> for details on the quantities
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displayed in this window.
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=== JT4
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JT4 is designed especially for EME on the microwave bands, 2.3 GHz and
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above.
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- Select *JT4* from the *Mode* menu. The central part of the main
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window will look something like this:
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image::VHF_controls.png[align="center",alt="VHF Controls"]
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- Select the desired *Submode*, which determines the spacing of
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transmitted tones. Wider spacings are used on the higher microwave
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bands to allow for larger Doppler spreads. For example, submode JT4F
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is generally used for EME on the 5.7 and 10 GHz bands.
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- For EME QSOs some operators use short-form JT4 messages consisting
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of a single tone. To activate automatic generation of these messages,
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check the box labeled *Sh*. This also enables the generation of a
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single tone at 1000Hz by selecting Tx6, to assist in finding signals
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initially. The box labeled *Tx6* toggles the Tx6 message from 1000Hz
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to 1250Hz to indicate to the other station that you are ready to
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receive messages.
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- Select *Deep* from the *Decode* menu. You may also choose to
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*Enable averaging* over successive transmissions and/or *Enable deep
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search* (correlation decoding).
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image::decode-menu.png[align="center",alt="Decode Menu"]
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The following screen shot shows one transmission from a 10 GHz EME
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QSO using submode JT4F.
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image::JT4F.png[align="center",alt="JT4F"]
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[[VHF_JT65]]
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=== JT65
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In many ways JT65 operation on VHF and higher bands is similar to HF
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usage, but a few important differences should be noted. Typical
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VHF/UHF operation involves only a single signal (or perhaps two or
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three) in the receiver passband. We recommend that you check *Single
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decode* on the *Settings -> General* tab, and do not check *Two pass
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decoding* on the *Advanced* tab. With VHF features enabled the JT65
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decoder will respond to special message formats often used for EME:
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the OOO signal report and two-tone shorthand messages for RO, RRR, and
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73. These messages are always enabled for reception; they will be
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automatically generated for transmission if you check the shorthand
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message box *Sh*. *Deep* on the *Decode* menu will be automatically
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selected. You may optionally include *Enable averaging*, *Enable Deep
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search*, and *Enable AP*.
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The following screen shot shows three transmissions from a 144 MHz EME
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QSO using submode JT65B and shorthand messages. Take note of the
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colored tick marks on the Wide Graph frequency scale. The green
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marker at 1220 Hz indicates the selected QSO frequency (the frequency
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of the JT65 Sync tone) and the *F Tol* range. A green tick at 1575 Hz
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marks the frequency of the highest JT65 data tone. Orange markers
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indicate the frequency of the upper tone of the two-tone signals for
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RO, RRR, and 73.
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image::JT65B.png[align="center",alt="JT65B"]
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=== QRA64
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QRA64 is designed for EME on VHF and higher bands; its
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operation is generally similar to JT4 and JT65. The following screen
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shot shows an example of a QRA64C transmission from DL7YC recorded at
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G3WDG over the EME path at 24 GHz. Doppler spread on the path was 78
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Hz, so although the signal is reasonably strong its tones are
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broadened enough to make them hard to see on the waterfall. The
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triangular red marker below the frequency scale shows that the decoder
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has achieved synchronization with a signal at approximately 967 Hz.
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image::QRA64.png[align="center",alt="QRA64"]
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The QRA64 decoder makes no use of a callsign database. Instead, it
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takes advantage of _a priori_ (AP) information such as one's own
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callsign and the encoded form of message word `CQ`. In normal usage,
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as a QSO progresses the available AP information increases to include
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the callsign of the station being worked and perhaps also his/her
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4-digit grid locator. The decoder always begins by attempting to
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decode the full message using no AP information. If this attempt
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fails, additional attempts are made using available AP information to
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provide initial hypotheses about the message content. At the end of
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each iteration the decoder computes the extrinsic probability of the
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most likely value for each of the message's 12 six-bit information
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symbols. A decode is declared only when the total probability for all
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12 symbols has converged to an unambiguous value very close to 1.
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For EME QSOs some operators use short-form QRA64 messages consisting
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of a single tone. To activate automatic generation of these messages,
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check the box labeled *Sh*. This also enables the generation of a
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single tone at 1000Hz by selecting Tx6, to assist in finding signals
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initially, as the QRA64 tones are often not visible on the waterfall.
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The box labeled *Tx6* switches the Tx6 message from 1000Hz to 1250Hz
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to indicate to the other station that you are ready to receive messages.
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TIP: QRA64 attempts to find and decode only a single signal in the
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receiver passband. If many signals are present, you may be able to
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decode them by double-clicking on the lowest tone of each one in the
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waterfall.
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TIP: G3WDG has prepared a more detailed tutorial on using {QRA64_EME}.
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=== ISCAT
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ISCAT is a useful mode for signals that are weak but more or less
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steady in amplitude over several seconds or longer. Aircraft scatter
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at 10 GHz is a good example. ISCAT messages are free-format and may
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have any length from 1 to 28 characters. This protocol includes no
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error-correction facility.
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=== MSK144
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Meteor scatter QSOs can be made any time on the VHF bands at distances
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up to about 2100 km (1300 miles). Completing a QSO takes longer in
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the evening than in the morning, longer at higher frequencies, and
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longer at distances close to the upper limit. But with patience, 100
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W or more, and a single yagi it can usually be done. The
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following screen shot shows two 15-second reception intervals
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containing MSK144 signals from three different stations.
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image::MSK144.png[align="center",alt="MSK144"]
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Unlike other _WSJT-X_ modes, the MSK144 decoder operates in real time
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during the reception sequence. Decoded messages will appear on your
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screen almost as soon as you hear them.
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To configure _WSJT-X_ for MSK144 operation:
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- Select *MSK144* from the *Mode* menu.
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- Select *Fast* from the *Decode* menu.
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- Set the audio receiving frequency to *Rx 1500 Hz*.
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- Set frequency tolerance to *F Tol 100*.
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- Set the *T/R* sequence duration to 15 s.
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- To match decoding depth to your computer's capability, click
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*Monitor* (if it's not already green) to start a receiving sequence.
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Observe the percentage figure displayed on the _Receiving_ label in
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the Status Bar:
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image::Rx_pct_MSK144.png[align="center",alt="MSK144 Percent CPU"]
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- The displayed number (here 17%) indicates the fraction of available
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time being used for execution of the MSK144 real-time decoder. If
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this number is well below 100%, you may increase the decoding depth
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from *Fast* to *Normal* or *Deep*, and increase *F Tol* from 100 to
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200 Hz.
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NOTE: Most modern multi-core computers can easily handle the optimum
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parameters *Deep* and *F Tol 200*. Older and slower machines may not
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be able to keep up at these settings; at the *Fast* and *Normal*
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settings there will be a small loss in decoding capability (relative
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to *Deep*) for the weakest pings.
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- T/R sequences of 15 seconds or less requires selecting your
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transmitted messages very quickly. Check *Auto Seq* to have the
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computer make the necessary decisions automatically, based on the
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messages received.
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- For operation at 144 MHz or above you may find it helpful to use
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short-format *Sh* messages for Tx3, Tx4, and Tx5. These messages are
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20 ms long, compared with 72 ms for full-length MSK144 messages.
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Their information content is a 12-bit hash of the two callsigns,
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rather than the callsigns themselves, plus a 4-bit numerical report,
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acknowledgment (RRR), or sign-off (73). Only the intended recipient
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can decode short-messages. They will be displayed with the callsigns
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enclosed in <> angle brackets, as in the following model QSO
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CQ K1ABC FN42
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K1ABC W9XYZ EN37
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W9XYZ K1ABC +02
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<K1ABC W9XYZ> R+03
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<W9XYZ K1ABC> RRR
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<K1ABC W9XYZ> 73
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+
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NOTE: There is little or no advantage to using MSK144 *Sh*
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messages at 50 or 70 MHz. At these frequencies, most pings are long
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enough to support standard messages -- which have the advantage of
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being readable by anyone listening in.
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=== Echo Mode
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*Echo* mode allows you to make sensitive measurements of your own
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lunar echoes even when they are too weak to be heard. Select *Echo*
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from the *Mode* menu, aim your antenna at the moon, pick a clear
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frequency, and toggle click *Tx Enable*. _WSJT-X_ will then cycle
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through the following loop every 6 seconds:
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1. Transmit a 1500 Hz fixed tone for 2.3 s
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2. Wait about 0.2 s for start of the return echo
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3. Record the received signal for 2.3 s
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4. Analyze, average, and display the results
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5. Repeat from step 1
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To make a sequence of echo tests:
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- Select *Echo* from the *Mode* menu.
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- Check *Doppler tracking* and *Constant frequency on the Moon* on the
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Astronomical Data window.
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- Be sure that your rig control has been set up for _Split Operation_,
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using either *Rig* or *Fake It* on the *Settings | Radio* tab.
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- Click *Enable Tx* on the main window to start a sequence of 6-second
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cycles.
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- _WSJT-X_ calculates and compensates for Doppler shift automatically.
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As shown in the screen shot below, when proper Doppler corrections
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have been applied your return echo should always appear at the center
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of the plot area on the Echo Graph window.
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image::echo_144.png[align="center",alt="Echo 144 MHz"]
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=== Tips for EME
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Current conventions dictate that digital EME is usually done with
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JT65A on the 50 MHz band, JT65B on 144 and 432 MHz, and JT65C on 1296
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MHz. On higher microwave bands typical choices are JT65C or one of
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the wider QRA64 or JT4 submodes, depending on the expected amount of
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Doppler spread. JT4 and JT65 offer message *Averaging* -- the
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summation of subsequent transmissions that convey the same message --
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to enable decodes at signal-to-noise ratios several dB below the
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threshold for single transmissions. These modes also allow *Deep
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Search* decoding, in which the decoder hypothesizes messages
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containing known or previously decoded callsigns and tests them for
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reliability using a correlation algorithm. Finally, JT65 and QRA64
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offer _a priori_ (AP) decoding, which takes advantage of naturally
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accumulating information during a QSO. The following tutorial aims to
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familiarize you with these program features, all of which are of
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special interest for EME and other extreme weak-signal conditions.
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As a starting point, configure _WSJT-X_ as follows:
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.Settings | General:
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- *My Call* = W9XYZ
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- Check these boxes: *Enable VHF/UHF/Microwave features*, *Single
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decode*, *Decode after EME delay*
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.Settings | Advanced:
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- *Random erasure patterns* = 7, *Aggressive decoding level* = 0,
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*Two-pass decoding* = _unchecked_, *Waterfall spectra* = _Most sensitive_
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.Main window menus:
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- *View* = Message averaging
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- *Mode* = JT65
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- *Decode:* *Deep* selected, *Enable averaging* checked,
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*Enable deep search* unchecked, *Enable AP* checked
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.Main window:
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- *F Tol* = 500, *Rx* 1500 *Hz*, *Submode* = B, *Sync* = 0
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- *DX Call*, *DX Grid:* both empty
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.Wide Graph:
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- *Bins/Pixel* = 3, *N Avg* = 10
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- Adjust the width of the window so that the frequency range extends
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up to at least 2400 Hz.
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If you have not already done so, install the sample files available
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for <<DOWNLOAD_SAMPLES,download>>. Select *File | Open* and navigate
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to ...\save\samples\JT65\JT65B\000000_0001.wav.
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The waterfall should look something like the snapshot below. A barely
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visible vertical trace appears at 1300 Hz. This is the synchronizing
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tone of a simulated JT65B signal with SNR = -26 dB.
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image::EME_Deep_0.png[align="center",alt="EME_Deep_0"]
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The decoder recognizes the sync tone of a JT65 signal, but is unable
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to decode it, producing only this line in the _Single Period Decodes_
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panel:
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0001 -28 2.5 1300 #*
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Press *F6* repeatedly, to read subsequent files. When
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five files have been read your display should look like this:
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image::EME_Deep_1.png[align="center",alt="EME_Deep_1"]
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The message `CQ K1ABC FN42` appears in the _Average Decodes_ panel,
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flagged with the <<Decoded_Lines,end-of line label>> `f3`. The label
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means that decoding was accomplished with the Franke-Taylor
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algorithm, using the average of 3 transmissions.
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The _Message Averaging_ window now looks like this:
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image::EME_Deep_2.png[align="center",alt="EME_Deep_2"]
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The `$` symbols mark lines corresponding to transmissions used in the
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most recent attempt toward an average decode.
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Hit the *F6* key again to read the sixth file. You should now see the
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message `K1ABC G4XYZ IO91` displayed in the _Average Decodes_ panel,
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again with the `f3` label.
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Now pretend you are K1ABC (enter `K1ABC` and `FN42` as *My Call* and
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*My Grid* on the *Settings | General* tab). Click *Clear Avg* and
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double-click *Erase* to start with a fresh screen. Open the files
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000000_0002.wav and 000000_0004.wav. You should now see the message
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`K1ABC G4XYZ IO91` in the _Average Decodes_ panel. Its end-of-line
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flag `a22` indicates that this decode used *My Call* as _a priori_
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(AP) information of type 2 (see Table 1 in <<AP_Decoding,AP
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Decoding>>), and is based on the average of 2 transmissions.
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You might wish to experiment with other combinations of entries for
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*My Call*, *DX Call*, and *DX Grid*, and with toggling the various
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options of the *Decode* menu on and off. For best sensitivity, most
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users will want to use *Deep* decoding with *Enable averaging*,
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*Enable deep search*, and *Enable AP* all turned on.
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