W7GJ

CHECKLIST & TIPS FOR SUCCESSFUL
50 MHZ EME CONTACTS USING JT44 MODE

INTRODUCTION

Why EME on 6m?

Independent of high geomagnetic latitude, which makes TE, F2 infrequent and/or impossible
Declining solar cycle further reduces chances for ionospheric 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
Provides another way for DXCC countries to complete WAS
3/4 million kilometer path - the Ultimate DX!
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 6m EME viable

New generation of computer-optimized antennas for higher gain
Commercial HF amplifiers beginning to include the 6m band (Yaesu, Icom, Acom, etc..) so it is easier to run 1 kw on 6m
JT44 Mode offers more than 15 dB sensitivity compared to CW
6m now available in most of Europe (but many countries still have restrictive power/ERP limits)
Japanese hams (very active on 6m and in DXpeditioning) are permitted to operate 6m EME with JT44 beginning in January, 2004

STATION REQUIREMENTS

Station EME Calculator

Provides a way to assess your system and determine who you can run a sked with
Found on the JT44 "ECHO MODE" screen:

If you can detect your own ECHO MODE echoes louder than "-33 dB" during an optimum time of month, you should be able to complete with W7GJ

Antennas

14 dBd seems to be a good target size for a "real" EME antenna

This size antenna is capable of contacting other similarly sized stations (provided each has 1000w)
Additional ground gain (while pointing on the horizon) counts toward the 14 dBd gain figure
Most 6m stations only have antennas aimed at the horizon (which is fortunate, since small antennas NEED the extra 3-5 dB ground gain)

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

M-Squared 6M7JHV yagi (31' long boom) aimed on the horizon (with ground gain)
M-Squared 6M11JKV yagi (69' long boom) aimed skyward (without ground gain)

Examples of next larger class of antennas (approximately 15-15.5 dBd) are:

One M-Squared 6M7NAN yagi (41' long boom) aimed on the horizon (with ground gain)
Two M-Squared 6M9KHW yagis (49.5' long booms) aimed skyward (without ground gain)
Four M-Squared 6M5X yagis (18' long booms) aimed skyward (without ground gain)

Recommend putting up the largest single yagi possible, as high as possible (unless building a fully steerable 4 yagi array)
Low loss feedline is very important (and fortunately, the loss at 50 MHz is not very high)

Low Noise External Preamplifier

Useful at quiet times of month
Overcomes high receiver noise figure
Usually used in the shack (unless transmission line loss exceeds 1 dB)

Learning JT44

Many tricks to get the last few dB of sensitivity from the program
Computer does NOT simply do all the work for you - experienced operator involvement is required
Essential to practice locally with other stations before trying JT44 on an actual EME sked

SCHEDULING

Choose "Best Time of Month"

6m EME is challenging even under most optimum conditions
Minimize predictable "Degredation"

Distance to the moon
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 aimed on the horizon)

Tropo ducting
F2 (watch time of day and direction)
High K index
High A index

Ground Gain

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
Two examples for different height antennas

Upper Ground Gain Lobe(s) often better

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

Multiple Common Window Opportunities (even for horizon-only stations)

Changing moon declination throughout the month provides common horizon windows with many places on earth
Moonrise-Moonrise, Moonset-Moonset, Moonset-Moonrise., Moonrise-Moonset options
Adding Second Ground Gain Lobe further extends the number of common window possibilities

JT44 SETUP

Computer Required

Speed of at least 150 MHz recommended
Computer interface required for PTT and sound card audio lines (typical PSK interface is fine)

Accurate Computer Clock Timing Essential

Programs updating time automatically through the Internet (such as Dimension 4)
GPS units best for remote locations without Internet access

Receiver

Flat audio output between 1200 and 1800 Hz
Widest USB IF filters
Disable any "tone control" or audio filtering
AGC OFF (if possible)

Audio Level

JT44 screen should register zero dB
Adjust level with RCVR volume control and/or Windows computer sound card recording level control

Specify Station to be Called

Enter callsign in "TO RADIO" window on left side of the JT44 window

If callsign is included in the file "CALLSIGN.TXT", you can also press the "LOOKUP" button and see the station's grid locator

Select Proper Transmitting Sequence

Shown on the right hand side of the JT44 window
Agreed upon in advance

Select Standard Message Text Generation

Automatically formats messages for use with averages
Permits use of FOLD option by receiving station

SYNC Levels - Indicate reliability of the decoding

Act as a "Threshold" level for accumulating a received message into the lower Average Message window
Usually set to Sync 1 for weak callsigns
Lowest Sync 0 setting can be used for reports

Carefully watch DT and DF for consistent values
Watch for reports in character average columns

Typical Example of Proper Setup

JT44 screen shows proper audio levels (as indicated by the display in the lower center of the screen as well as the green audio input (lined up with the small "tick marks" on both sides of the JT44 signal window)
"EME" messages box has been checked
Station to be called (W1JJ in this case) is entered in the "To Radio" box
"Gen Std Msgs" button has been pushed to create the proper messages shown
Note also the typical "DT" for the message received, showing it was indeed a signal delayed by the path distance to the moon and back (should show approximately 3 second delay if both computer clocks are properly set)

ACTUAL JT44 OPERATION

Do not change receiver frequency (during receive sequence)
Do not change transmitter frequency (during transmit sequence)
Weak Birdies/Multiple Stations Can be Viewed (carrier birdies or JT44 sync tone) on slow waterfall displays

Big Spectrum (WSJT version 3.8.1 and later) provides summary of what has been processed during receiver period
SPECTRAN program provides sensitive spectral display, but requires second computer for real time monitoring:

Above image shows a weak SPECTRAN trace from K7BV, approximately 10 dB above the background noise. This clearly shows where the signal is, and where the narrow JT44 "FREEZE" filter safely can be set. The weak signal observed above did not decode in JT44.

Simple Messages

Usually stronger than -24 dB for reliable individual decode
Shown sequentially in the upper JT44 window

Message Average

Single line shown in the lower section of the main JT44 window

Averages all messages that exceed the SYNC threshold set by the user
Can accumulate an average of much weaker messages
Remember to press "CLEAR AVG" when you begin receiving a new (different) message, or the average line will just become increasingly garbled

CLIP function

Reduces effects from static crashes but sacrifices some sensitivity
Normally set at zero

ZAP function

Reduces effects from birdies but sacrifices some sensitivity
Normally set at zero

FREEZE filter

Used to filter out birdies and/or separate multiple stations
Filter width adjusted by changing the TOL setting
Increases JT44 sensitivity slightly
Must first make sure you know where station is. If signal is strong enough, a spike will be shown at the frequency of the SYNC signal, shown on the RED JT44 line
Set FREEZE filter by moving mouse to peak on RED line (until the units values under the graph turn red), click on the spike, and then check the FREEZE box. (above the date and time display near the bottom of the JT44 screen).

The above image shows use of a wide FREEZE filter with a TOL of 400 Hz.

Narrow FREEZE filter on K7BV
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 very weak "SYNC 0, -33 dB" , 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! The proper frequency to set the freeze filter was determined from previous transmissions, and also by watching the signal with SPECTRAN on a separate computer.

Watch DT and DF (values shown just to the left of each received message)

Keys to whether you should INCLUDE or EXCLUDE an individual message from the lower Average Message window
The lower you set the SYNC threshold, the closer you must watch DT and DF values to make sure you are decoding a "real" message
DT should indicate an appropriate delay by the trip to the moon and back (typically around 3 seconds)
DF should show consistent frequency difference (unless you have changed your receiver tuning)

FOLD function

Useful for decoding callsigns
Press FOLD button below moon position display window

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

Character Averages

Most sensitive display in JT44
Can be used very effectively to watch for one or two character messages (RO, RR, 73, SK, FB, CU or R)
Two columns to the right of individual messages averages odd and even characters of a message
The last single column to the right represents the average of all message characters

Reports from K7BV in the CHARACTER AVERAGE columns

The above image shows "OO O" in the character columns. Although this is shown as a very weak "SYNC 1, -30 dB" signal. the reports are very clearly shown in the character average columns (partly due to the fact that the SYNC was set to zero and a narrow FREEZE filter was being used). Please do not be confused by the DT (which should be around 3) displayed here (the transmitting station's computer clock was 4 seconds too fast)

REFERENCES

W7GJ's Pages

JT44 Tips and News
6m EME Tips
2m EME Tips
TRACKER, CALLSIGN.TXT, SPACE (for calculating clearance of any size fully steerable array) programs Download Page

K1JT's WSJT Home Page
N0UK's JT44 Schedule/Chat Page
Hamtronics (source of LNY-50 Preamp)

CONCLUSION

Examples of successful W7GJ contacts with single yagi DXpedition stations

CY9DH
ES8X

This page last updated on October 21, 2003