The 50 MHz amateur radio band may be known as the Magic Band, but it is probably one of the more difficult and challenging ham bands for sending signals to the moon and back (Earth-Moon-Earth communications). This is in comparison to the fact that 6m stations in many parts of the world do have occasional access to ionospheric propagation that makes it possible for contacts over long distances between relatively very small stations. On EME, however, signals are usually erratic, unpredictable, and very weak, and relatively large, high power stations are required in order to achieve success. Despite the difficulty in completing a contact this way, EME at least presents a way that CAN be used to complete contacts when ionospheric propagation is not available option between the two 6m stations.
The information presented on this page is basically to assist 6m stations in making their first successful contacts on this particular band. People interested in further information about more serious EME operations and techniques are invited to visit my web page of Tips for 2m EME. With the correct equipment and planning, the success of a "moonbounce" contact on the Magic Band can be greatly increased.
Also, please see the information on the new JT65 mode . This makes it possible gain an additional 10-16 dB compared to CW, thereby GREATLY enhancing the chance of successfully completing a 6m EME contact!
1. BASIC SYSTEM REQUIREMENTS - The nice thing about EME communications is that the gain at one larger station can compensate for lower gain at the station at the other end of the path. I completed my first 6m EME contact using a 30' (9m) long 7 element yagi, 20' (6m) above the ground, along with 1500 watts from a homebrew 8877 amplifier. With the current W7GJ G.L.E.A.P. array, it is possible to complete contacts with stations only using only a single good yagi (such as a 7 element 6M7JHV, with 11 dbd gain) pointed at the horizon (therefore developing added ground gain) and running 1 Kw output. Of course, if a station has more antenna gain and more power output, or both stations can see the moon on the horizon at the same time (combining the ground gain from both stations), the chances for success are increased. If you can hear your own echoes at some point while the moon is near your horizon, then I should be able to make a contact with you.
2. THE HORIZON - A MIXED BLESSING - Most 6m operators use simple yagis that are always pointed at the horizon. This is good because it results in "ground gain" (see section below), and makes even a single yagi perform like a much larger antenna pointed skyward. However, you need to be aware of local obstructions (such as buildings or mountains) and noise sources (such as cities, high power TV transmitters, etc.), and avoid times of month when the moon is in that direction when it is near the horizon. However, please remember - when a single yagi antenna is pointed at the horizon, there are higher ground gain lobes that can usually be used to "look above" many local obstructions! I have completed with many single yagi stations while the moon was up around 15 degrees for them - right in front of their second ground gain lobe!
The direction of moonrise and moonset move over the course of the month, due to the fact that the moon's orbit is tilted with respect to the Earth's equator. Often, therefore, over the course of the month, a time can be found when the moon is located in a "preferred" direction.
Because 6m it is the lowest frequency VHF band, it is also subject to the most "interference" by the ionosphere, which can adversely affect (refract, scatter, absorb, rotate, etc. etc.) the signals on their way out to the moon as well as on their return. These effects are increased when the antenna is pointed at the horizon, since the signals have to go through more ionosphere that is "in the way" of the moon. 6m signals can also be the subject of tropospheric "bending", which can prevent signals directed at the horizon from taking straight off into space. Success is enhanced by avoiding times when horizon aimed antennas might encounter the various factors that are likely to interfere with signals traveling to the moon and back.
3. PREAMPLIFIER - Most stations do not use a tower mounted preamplifier on 6m EME, unless they have long feedlines. However, it is very important to make sure that the receiver is as sensitive as possible. In order to make sure that the system noise figure is as low as possible, it is suggested that a low noise GaAs FET preamplifier be used ahead of the receiver. Many stations think that their transceivers and systems are already working great, since they hear signals 30 db over S9 during an F2 opening. And, many common 6m transceivers are designed especially to be able to accomodate such very loud signals. However, when trying to copy a weak CW signal off the moon that may only briefly barely come up to the noise level, it is essential to make sure the receiver system is as sensitive as possible.
As an example, my IC706 transceiver (my first 6m rig) seemed to hear loud stations fine during Es openings. However, I noticed that switching in a low noise GaAsFET preamplifier ahead of it on receive made an UNBELIEVABLE DIFFERENCE with weak signals! With the preamp (with over 20 db gain) added, the background (no signal present) noise on the IC706 S-meter just barely began to move, indicating that the noise figure of the receiver was now set by the preamp. And that it had been REALLY insensitive before!!!
Remember - EME is the ultimate test of your station! This is NOT like waiting for an S-9 signal to pop out of the noise during an F2 opening!. ANY receiver can hear an S-9 signal. You will need to make sure your receiver is at the peak of its sensitivity in order to hear an EME signal that is down at the noise level.
Very effective and economical preamplifiers can be obtained from Hamtronics. You would want either the LNY-50 or LNK-50 (the unit installed in a case with BNC connectors). PLease note that either of these preamps MUST be installed in the RECEIVE line only! They DO NOT include automatic RF switching! Some other preamps available from other manufacturers include RF relays built into them so you can simply install them between your low power transceiver and antenna without blowing up the preamp, but these units are NOT that type (which is why these are much less expensive). If you already have some sort of coaxial relay to switch your antenna between your receiver and transmitter, you should be OK with either of the LNK or LNY Hamtronics preamps. It you have an amplifier, it must also have some sort of built in coaxial relay, and perhaps you can connect the preamplifier in the receive line at that point. I always also like to add a relay to either ground the preamp input or connect it to a 50 ohm resistor when you are not at the station, or you are in the XMIT mode- this provides additional protection for the preamp.
For either of the above preamps, you will also have to provide a separate small 12 VDC power supply, such as one of the low current "wall transformer" units that simply plugs into an electrical outlet. It is very important to make sure that your 12 VDC power supply is completely separate from the power supply that is powering your XMTR or TRANSCEIVER, since often there are large voltage spikes on that DC power supply line when the XMTR is keyed, or when the rig is turned on. Any such transients can (and will) quickly blow out your preamp. Your preamp is protected from this if it is on its own inexpensive power source.
4. GROUND GAIN - USE IT TO ADVANTAGE! If you are located on level ground, have a horizontally polarized antenna, and have a flat, clear horizon, you will probably enjoy a certain amount of "ground gain". This comes from additive reflections when the moon is near the horizon, and can amount to as much as an extra 6 db in signal strength. Often on 6m, stations only have small antennas that are fixed on the horizon, and they will need whatever ground gain can be developed at their location.
Such ground gain depends on the height of the antenna above the ground, the ground conductivity, and the terrain around the antenna. The best ground gain would be realized by having a tall tower on a small island surrounded by salt water. Typically, though, we all have some amount of ground gain. This is usually what makes it possible for a station to make a contact on 6m EME.
The ground effect creates various vertical lobes in a single yagi pointed at the horizon. The number of ground gain lobes and their elevation depends on how high the antenna is above ground( in terms of wavelengths). This comparison is shown here. As you can see from this comparison, my single 21m long yagi, 21m above the ground, my main lobe is around 4 degrees, and I have a second lobe up around 11.5 degrees (which is still with about 1.5 db of the main lobe in gain). Both of these lobes are substantially higher than the "free space gain" (approximately 14 dbd) for that antenna when it is pointed up toward the sky. I have heard echoes and made contacts off BOTH of those lobes. Using the main lobe of course is preferred because it has the most forward gain. However, when there are other factors involved that can adversely affect the main lobe (see Point #2 above), the higher lobe(s) may still get through.
As an example, I used to run moonbounce tests with the late W8ZH on his moonset. His antenna was the same as my single yagi (charted above), but since antenna was on a 150' (46m) tower with a clear shot as far as you could see with a telescope, he had more (and lower) lobes. Unlike my antenna (with basically two lobes providing extra ground gain), his had 5 lobes all with greater than the antenna free space gain - and 3 of them were under 10 degrees elevation. My point is that W8ZH was always good copy off the moon on 6m - but when his moon was below 10 degree in elevation, I never heard him at all! While the higher lobes made it through, the local tropospheric conditions always "captured" the signals from his lower lobes.
I noticed the same thing during 6m EME skeds with single yagi stations in Europe during early December, 2001. Signals were repeatedly copied and were building as the moon began dropping in front of their antennas and I was very encouraged that the contact was going to be completed easily as soon as the moon dropped a little closer to their horizon. However, I never heard them after the moon was below 8 degrees elevation for them. I attribute this not to tropo ducting, but F2 interference (since there was a region of high MUF just west of Europe at the time).
You also may be able to coordinate a time when the moon is in front of the main lobe at one station at the same time it is in front of the second lobe at another station. Although this condition does not last very long, and the chances are slim of conditions "properly lining up" for those precious few minutes, it is a proven way to make a 6m EME contact when the free space path calculations show that the antennas and/or power should be too small.
5. FINDING THE MOON - Even if you cannot elevate your antenna, and can only operate on moonrise and moonset, knowing where to point your antennas so they are aimed at the moon is very important. In 1973, I wrote a simple computer program to provide this information and there are now many version of this program for all kinds of small personal computers. If you have a small computer or know someone who does have access to one, you should have no problem locating a version of the program which will run on that computer and provide you the aiming information you will need. This DOS program, TRACKER, has been updated over the years, and also provides a number of options, including printout only when the moon is near the horizon and/or showing your moon position in addition to the position at another station at the same time. You are invited to download it and its associated program files free of charge from my download page.
6. CHOOSING OPERATING TIMES FOR BEST EME CNDX- Because the moon moves closer (perigee) and farther (apogee) from the Earth during the course of each month, there is about a 2 db difference in signals attributable to the distance alone. You will generally be more successful on moonbounce if you operate near perigee. Another consideration is the background sky noise. The sky behind the moon is not always quiet and, at times (particularly during the part of each month that the moon is further south in the sky), it can be extremely noisy. The quieter the sky behind the moon, the easier it will be to hear moonbounce signals. The quietest time is generally just after the moon passes through its most northerly declination for the month and is moving southward in the sky. Of course, if the moon is too close to the sun, it will also be too noisy to operate successfully and for that reason most stations avoid operating within one day of "new moon".
My old moon tracking program TRACKER (see above) shows approximate background sky temperature at 50 MHz, moon distance, and the db equivalent sum of their degrading effects. This makes it easy to select times of most when the chances for success are most likely.
7. FREQUENCY AND DOPPLER SHIFT -The usual convention on EME is to refer to the frequency where the CW signal will be ZERO BEAT. So, if you are using a transceiver, make sure that the frequency is properly set to provide a zero beat CW signal on the proper frequency (some transceivers automatically offset the transmitter frequency 400 to 600 hertz in the CW mode, from what is shown on the display). On JT65, simply set the USB frequency to the desired sked frequency.
Doppler shift is not that critical at 50 MHz, and I find that moon echoes from both stations are usually within about 150 Hz, provided the stations agree to transmit on the same frequency. 6m EME signals are very weak, and it can take quite a while to find and carefully tune them in so that they are on the correct frequency for avery narrow DSP audio filter. Once you begin to transmit, please do not change the transmit frequency! You should use a separate receiver or a transceiver's RIT CONTROL to tune around.
8. PATIENCE -In addition to the moon moving in front of various antenna lobes of an antenna that is pointed at the horizon, there also are many propagation factors involved (such as ionosphere absorption/refraction, faraday polarity rotation, scintillation and libration fading, auroral scattering, tropospheric ducting, etc.) that can cause the signals to appear or disappear. Basically, it all means that there are lots of reasons why a station may not hear you at the same time you hear him, or why you may not hear anything at all on a given day. Please do not become discouraged and give up! Conditions change, and your results can be entirely different later in the day or on another day.
It is not all unusual on 6m, for signals to peak up for only 10 seconds over a 15 minute period. For that reason, it is especially important to pay careful attention to transmit for the full period every sequence, and be ready and on frequency for the weak signal to suddenly - and briefly - appear.
9. SEQUENCING & SCHEDULES -Make sure that you use the proper QSO procedures and transmitting sequences. On 50 MHz, unless otherwise specified, CW EME schedules use 1 minute transmit periods, with each station alternately transmitting for the full 1 minute sequences. Both stations must synchronize to WWV or some other standard before the schedule. The standard convention is that the more eastern station transmits during the "even" minutes (and the more western station transmits during the "odd" minutes). The "even" (or "first") minutes are defined by the number that is displayed for that minute on a digital clock. For example, even/first minutes would be 0600z-0601z, 0602z-0603z, etc.
On JT65 mode, one minute periods are also used. Here the sequence is selected by checking the or not checking the "TX FIRST" box on the JT65 screen.
Faraday Rotation on 6m typically takes around 12 minutes, so schedules are usually at least twice that long, in order to provide for at least one polarity peak for each station. It also can be very helpful, when scheduling with a single yagi fixed on the horizon, to run a schedule long enough to encompass two ground gain lobes.
10. EXCHANGES & REPORTS -Because of the relatively weak signals, CW previously was used exclusively for EME schedules with large stations on 50 MHz, and usually speeds between 13 wpm and 17 wpm usually seem to work best. Faster speeds cause the dots to get lost in the fast fading and/or narrow DSP audio filters, and slower speeds don't let both callsigns be received during a very short signal peak. For smaller 50 MHz stations, JT44 must be used. In order to have the JT44 program follow the standard EME exchanges described above, it is necessary to select the "EME MESSAGES" box, and also to press the "GENERATE STANDARD MESSAGES" button. More tips on using JT44 on 6m is on my JT44 web page. The system of exchanging reports, however, is basically the same as used on CW.
To make sure that you take advantage of the QSB signal peaks on CW, you should always send callsigns alternately, rather than repeating the same callsign. For example, a proper transmitting sequence during a schedule would be filled with "OZ4VV W7GJ OZ4VV W7GJ OZ4VV W7GJ", not "OZ4VV OZ4VV de W7GJ W7GJ W7GJ". If you are answering a CQ, best success is usually had by sending your call 3 or more times for every time you send the callsign of the station you are calling. When using JT44, make sure that you are using the automatically-generated "standard texts" messages for the callsigns, and that you use the "EME" reports - this makes it possible for the other station to use the JT44 "FOLD" option and gain some additional readability on your signal.
The only signal report usually used on 50 MHz is a letter "O". When a station hears both callsigns being sent, he responds by sending O's in between callsign sets. An example would be "OZ4VV W7GJ OOOO OZ4VV W7GJ OOOO OZ4VV W7GJ OOOO". Obviously, because signals can peak (and then disappear) so quickly, it is important to transmit all the information together in as short a period as possible. When using JT44, at least the last 8 characters of the message should be OOOOOOOO.
When a station copies both callsigns and O's, he would respond by sending a full sequence of "RORORO". When RO's are received, the other station responds by sending a full sequence of "RRRR". The contact is complete when final R's are received by one of the stations.
11. COMPUTER PROGRAMS TO COPY WEAK SIGNALS-
Because signals are always very weak, it is extremely helpful to use one
of the computer programs to assist in finding weak signals, so you can
be sure to be listening on the correct frequency when they do peak up loud
enough to copy. One example is AF9Y's FFTDSPprogram.
Another excellent program, which has a simple built-in audio filter,
is SPECTRAN by I2PHD and
IK2CZL. A fully developed (LINUX) program with excellent audio filtering
options, developed especially for EME, is LINRAD
by SM5BSZ. And, of course, the real secret to success in working
6m EME is to use the new digital mode, JT65.
If you follow the above guidelines, you will
be well on your way to a good start on 6 meter EME and discover that afar
northern geomagnetic latitude and/or a bad solar cycle is not necessarily
the end to working DX on the Magic Band. 73 and good DX!
This page last updated on August 15, 2003