W7GJ

CHECKLIST & TIPS FOR SUCCESSFUL

50 MHZ EME CONTACTS USING JT44 MODE

(as provided in WSJT version 3.8.1)

INTRODUCTION

• Why EME on 6m?

• Independent of high Geomagnetic Latitude, which makes TE, F2  infrequent/impossible
• Declining Solar Cycle  further reduces chances for inonospheric propagation
• Makes up for unfavorable Geographic Location which does not provide effective Es links to ionospheric propagation, or has poor horizon
• Provides another avenue for working new DXCC countries, and also for DX stations to complete WAS
• The technical and operating challenge!

• 6m EME Characteristics Rapid Faraday Rotation (typically 10-15 minutes)

• Short Signal Peaks
• VERY weak signals
• Unpredictable Conditions  (even when  best  times of the month  are selected for activity)

• New Developments Make it Possible

• New Generation of Computer-Optimized 6m Antennas for  higher gain
• Amplifiers Beginning to Include 6m (Yaesu,  Icom,  Acom, etc.) so it  is easier to  run  1 kw on  6m
• JT44 Mode >10 dB over CW
• 6m now available in most of Europe (but many countries still have restrictive power/ERP limits)
• Japan (JT44 and EME permitted as of January 12, 2004)

STATION REQUIRMENTS

·         

• Station EME Calculator (provides a way to assess your system and determine who you can sked)

o        Found on JT44 “ECHO MODE” screen

o        If you can detect your own ECHO MODE echoes louder than “-33 dB”, during an optimum time of month, I should be able to complete with you.

• Antennas

o        14dBd seems to be a good target size for a “real” EME antenna

§         This size can work similarly-sized stations (provided each has 1000w)

§         Additional Ground Gain (while pointing on the horizon) counts toward 14 dBd gain figure

o        Examples of minimum sized (approximately 13-14 dBd) 6m EME antennas include:

§         M-Squared 6M7JHV yagi (31’ long) aimed on the horizon (with ground gain)

§         M-Squared 6M11JKV yagi (69’ long) aimed skyward (no ground gain)

o        Examples of the next larger class of antennas (approximately 15 to 15.5 dBd) are:

§         One M-Squared 6M7NAN yagi (41’ long) aimed on the horizon (with ground gain)

§         Two M-Squared 6M9KHW yagi (49.5’ long) aimed skyward (no ground gain)

§         Four M-Squared 6M5X yagi (18’ long) aimed skyward (no ground gain)

o        Recommend putting up largest single yagi possible, as high as possible (unless building a fully steerable 4 yagi array)

o        Low Loss Feedline

• Low Noise External Preamplifier

o        Useful at quiet times of month

o        Overcomes high receiver noise figure

o        Usually used in the shack (unless transmission line loss exceeds 1 dB)

• ·          Practice (absolutely essential to practice locally with other stations before trying JT44 on EME)

SCHEDULING

• Consider Time of Month to Minimize “Degradation”.  This varies according to:

o        Distance to the moon

o        Sky Temperature behind the moon

• Frequencies mutually agreed to in advance to avoid birdies and QRM (usually above 50.200)
• Avoid Interfering Factors (strongest when pointed on the horizon)

o        Tropo Ducting

o        F2 (watch time of day)

o        High K index

o        High A index

• Ground Gain

o        Single Beams Usually Have Two (at least) Good Ground Gain Lobes

§         Elevation and number of ground gain lobes depends on height of antenna above ground
§         Examples: http://www.bigskyspaces.com/w7gj/Groundgainlobes.htm

 o        Upper Lobe(s) Actually Often Better

§         Avoids local obstructions
§         Beams through less atmosphere
§         Provides additional chances to complete contact

o         Multiple Common Window Times

JT44 SETUP

• Computer Required

o         Speed of at least 150 MHz recommended

o         Computer interface required for PTT and sound card audio lines

• Accurate Computer Timing Essential

o        Internet (such as Dimension 4)

o        GPS

•   Receiver

o        Flat Audio 1200-1800 Hz

o        Widest USB IF Filters

o        No “tone control” or audio filtering

o        AGC OFF if possible

•   Audio Level

o        JT44 Should Register Zero dB

o        Adjust With Receiver Volume Control and/or Computer Sound Card Recording Level

• Birdies/Multiple Stations

o        Big Spectrum (WSJT version 3.8.1 and later)

o        SPECTRAN (provides sensitive real time display, but usually requires second computer)

Above image shows a weak Spectran trace of K7BV, approximately 10 dB above the background noise.  This clearly shows where the signal is, and where I can safely set the narrow JT44 “FREEZE” filter.  The corresponding signal did not decode in JT44.

o        ZAP Birdies (sacrifices some sensitivity)

• Select Standard Message Text Generation

o        Automatically Formats Messages for use with Averages

o        Permits use of FOLD Option by Receiving Station

• Select EME Reports

• Sync Levels

o        Sync 1 for Callsigns

o        Sync 0 for reports (carefully watch DT and DF for meaningful consistent values)

• Typical Example of Proper Setup

Note that this JT44 screen shows proper audio levels (as indicated by the indicator in the lower center of the screen and the green audio level signal lined up with the small “tick marks” on both sides of the JT44 signal window.  Also note that the “EME” messages box has been checked and the “Gen Std Msgs” button has been pushed to create the messages shown.

Note also the typical “DT” for the message received, showing it was indeed a signal delayed by the distance to the moon.

ACTUAL JT44 OPERATION

• Do not change receiver frequency (during receive sequence)
• Do not change transmitter frequency (during transmit sequence)
• Static Crashes and use of CLIP Function (sacrifices some sensitivity)
• FREEZE Filter/TOL settings (to filter out birdies and/or separate stations)

The above image shows set up of a very wide FREEZE filter with a TOL of 400 Hz.

 

The above image shows a relatively narrow FREEZE filter with a TOL of 100 Hz on a weak SYNC 1, -30 dB message.  Without the FREEZE filter, this message registered as a SYNC 0, -33 dB message, with no decode.  Note that the narrow FREEZE filter not only increased the SYNC level, but also permitted display of the signal reports in the character averages columns!

• Simple Messages (Usually stronger than -24 dB for decode)

• Message Averages (includes messages stronger than -30 dB)

o        Use FOLD Function (when trying to decode callsigns)

o        Clear Average Message Line (after callsigns are received)

o        Use FOLD Function (when trying to decode callsigns)

The above image shows a message that decoded, but apparently did not result by itself in clear callsigns.  However, when the message was folded by using the “FOLD” button (possible only when both halves of each message are identical), the callsigns are solid copy.

o        Use of DT and DF to SELECT/EXCLUDE individual messages

• Character Averages (averages last 4 pairs of characters of each message, and all 22 message characters for a single character average).  These are especially sensitive, and I recommend resetting the SYNC threshold to zero and watching each incoming message carefully for appropriate DT and DF, to see if a real signal has been received and generates special characters in the right hand columns.

The above image shows “OO O” in the character columns.  Although this is shown as a very weak SYNC 1, -30 dB message, the reports are very clearly shown in the character average columns.

 

o        Watch the two character average for two letter messages (such as OO, RO, RR ,73) in the last 8 or 10 spaces of each individual message

o        Watch the rightmost column for an R if message being sent is a string of (up to 22) R’s.

o        Also useful for CQ if put at the end of each message:

§         “W7GJ_W7GJ_W7GJCQCQCQCQ” (shows I am not calling another station and provides full opportunity to use the last 4 pairs of characters for average)

§         “W7GJ_CQCQCQW7GJ_CQCQCQ” (message also can be folded for best copy of callsign)

• Change Standard Transmitted Messages According to What You Have Copied

o        Do NOT simply mimic what you copied

o        XMIT the Next Message Below the Message Received

o        Contact is complete when one station receives final RRRR

• Essential to XMIT every sequence (since it is very unlikely that stations will copy each other at the same time)

REFERENCES

• W7GJ’s Pages (case sensitive)

o        JT44 Tips at http://www.bigskyspaces.com/w7gj/jt44.htm

o        6m EME Tips at http://www.bigskyspaces.com/w7gj/6memetips.htm

o        2m EME Tips at http://www.bigskyspaces.com/w7gj/emetips.htm

o        TRACKER, CALLSIGN.TXT file at http://www.bigskyspaces.com/w7gj/tracker.htm

• K1JT’s WSJT Home Page at http://pulsar.princeton.edu/~joe/K1JT/
• N0UK’s JT44 Schedule/Chat Page at http://www.chris.org/cgi-bin/jt44eme
• Hamtronics LNY-50 preamp at http:/www.hamtronics.com/

CONCLUSION

• Examples of single yagi success stories:

o        CY9DH DXpedition

o        ES8X DXpedition