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How To Get Started On EME

Moonbounce is "the ultimate long path DX". It's exciting and allows you to literally work the world on VHF and UHF. It's not as difficult as you may think. Here's how to get started on this most exciting mode. You can participate even with a single long yagi pointed at the horizon, so don't worry if you can't elevate your antenna to track the moon!

What you need
The Nature of EME
EME Operating Techniques
When and where to listen
Scheduling and Information Resources
Links to some interesting info on EME equipment and other stuff
Some examples of 2 meter EME Signals
EME Frequently Asked Questions

Earth and the moon

Earth and the moon as seen by the Galileo spacecraft (NASA)

Not too long ago, EME may have been beyond the reach of many hams. Not any more! There are thousands of active stations working EME on all bands from 50 MHz to 10 GHz. It really doesn't take a lot to get started. For example, W2RS has worked 37 stations on 2 meter EME with a single 3.2 wavelength yagi (CushCraft 3219), a brick amp putting out less than 200 watts, and a good preamp. With a single yagi system and high power, it's possible to work a lot more! The discussion that follows is slanted toward 2 meters... other bands are similar, but have their own requirements for equipment, slight variations in conditions, operating techniques, etc.

 What you need

To participate in EME, you will need an antenna with at least 12 dBd gain, at least 150 watts, and a good low noise preamplifier. Of course, more is better. You do not have to elevate the antenna to get started in EME. All of those contacts made by W2RS were at moonrise and moonset with the antenna aimed at the horizon. In fact, there is good reason for small stations not to elevate... see below. It helps to have the preamplifier mounted at or near the antenna, but is not absolutely necessary. With modern GaAsFET devices, really good preamplifiers abound.

A few comments on getting the most out of what you have. Using the best feedline you can is only common sense, so I won't say much about it... but use a good feedline. Don't cut corners with the antenna. Take the time to get all the elements perfectly aligned, and if you have stacked antennas, get all the booms lined up properly too. EME is very weak signal work and little things do make a difference. A little extra effort will pay off. If you're choosing an antenna or building an array for EME, give some thought to the pattern as well as the gain. Side and rear lobes often pick up noise and this can seriously detract from your ability to hear weak signals off the moon.

Filtering is an area that is best left to the individual. Some people listen with an SSB bandwidth filter and do very well. Others like to have a narrow IF filter and/or outboard AF filtering. DSP filters are also common and some swear by them. The bottom line with filtering is experiment. Find what works for you.

 The Nature of EME

EME signals fade in and out for a number of reasons. Sometimes you hear nothing for long periods of time, other times you will be amazed what you can hear. Don't become discouraged if it takes several attempts to hear your first signals, make your first contact, or to work a particular station.

The polarization of EME signals is constantly changing. Except for a few stations who can rotate or electrically switch the polarization of their antennas, this causes very deep QSB that can last from several minutes to several hours or even days. There is also such a thing as true one way propagation on EME, largely due to polarization shifting, so don't become discouraged if you experience this. Just keep trying.

The moon follows many cycles. The distance between the Earth and the moon is not constant. It varies, and generally there will be a perigee (moon closest to Earth) and an apogee (moon fartherst from Earth) each month. Path loss to the moon and back is roughly 2 dB less at perigee than at apogee. This can make a very noticeable difference for small stations. Also, the sky behind the moon can be very noisy at certain times. All planets, stars, etc. emit noise across the radio spectrum, and most EME systems are sensitive enough to hear this noise. Sky noise is generally at its worst when the moon is crossing the galactic plane (moon appears in the milky way), which occurs twice each month. Practically all software intended for EME use includes this data. You can download Z-Track from this site, but there are several other eqaully good programs available. On 2 meters, sky noise varies between a low of about 175 degrees Kelvin (rare) to over 3000 degrees Kelvin. The lower the better, and if it's much over 400 the smaller stations are in big trouble!

Signals also tend to exhibit a rapid, almost fluttery fading known as libration fading. This is caused by the irregular surface of the moon, which "rocks back and forth" slightly as viewed from Earth. Libration can cause signals to go goth above and below the average level. Libration peaks, which can last up to a couple of seconds at 2 meters, can actually help the small station make contacts they would not be able to otherwise.

Another phenomenon not specifically relating to the moon which should be mentioned is ground gain. Simply put, reflections from the ground in front of an antenna cause peaks and nulls at certain elevation angles when the antenna is pointed at the horizon. The peaks can theoretically be 6 dB over the gain of the antenna alone over perfectly conductiong, flat ground. In practice, it is somewhat less than that but can still make the difference between working a station and not working a station. That is why I said for small stations aiming at the horizon may actually be an advantage, assuming one does not have a marked increase in noise on the horizon. How high you can work the moon without elevating the antenna, and at what elevation angle the  peaks occur, depends on several factors, including the height of the antenna. Generally, 15 degrees or so is the upper limit and it may be much lower in some cases. Ground gain does not work as well with really high antennas as it does with lower ones.

Because the moon moves in relation to Earth, there is a slight doppler shift on EME signals. At moonrise, a 2m EME signal may be shifted up in frequency by as much as 350 Hz. The doppler slowly comes down, reaching zero when the moon is passing your longitude (due south or due north azimuth heading), then starts to shift in a negative direction, going as much as 350 Hz down by moonset. Always tune slightly with the RIT when looking for  a station on random. AF9Y, Mike, has written a program which can help you find the exact fequency of a station even when you can't yet hear the signal. It's called FFTDSP and is quite useful.

Because the round trip distance is nearly half a million miles, it takes over 2 seconds for a signal to travel from Earth to the moon and back to Earth again. Well equipped stations can actually hear their own signals echoed back from the moon when conditions are favorable.

 EME Operating Techniques

EME is weak signal work and almost all contacts are made with CW. Some of the well equipped stations occasionally try SSB just for fun, but it's the exception not the rule. As for CW speed, most operators are comfortable somewhere between 10 to 20 WPM. Fast CW tends to be difficult to copy when signals are very weak, and too slow CW gets chopped up by libration fading, so there has to be a compormise somewhere. Good clean sending is an advantage, and many operators recommend increasing the length of the dits (increase the weight) slightly to make them stand out more. A dit lengh of 1.2 times normal seems to work well here.

Random operation (calling CQ or answering CQ's) is common, but for very small stations better success will be had on prearranged schedules. Schedules are generally run for 30 minutes, but may vary. Random operation is at the low end of the band (144.000 to 144.045) with schedules taking place above that all the way to 144.170.

Because signals are weak and not always out of the noise, almost all contacts are made with accurately timed transmit and receive sequencing. One minute sequencing is common on random, and two minutes is the norm for skeds (on 2m), athough some operators prefer 2 minutes on random as well. For skeds, the convention is that the easternmost station will transmit the first 2 minutes at the top of each hour. Please note this means the period :30 to :32 is a western sequence, so skeds starting on the half hour will be the westernmost station transmitting first. It just follows right around, like so: The :00 to :02 period is eastern, :02 to :04 is western, :04 to :06 is eastern.... etc. On random, it makes little difference which sequence a CQ'ing station uses.

Setting your frequency correctly is very important. For schedules, set your transmit frequency to the prearranged schedule frequency and then do not move it. Let your schedule partner find you. During receive you should be tuning +/- 500 Hz or so with your RIT, second VFO, or whatever. What to do if you find your schedule partner more than a few hundred Hz off frequency is a dilemma. It is best not to move early in the schedule, as he may have already located your signal. Sometimes it is worth moving late in a schedule if you are not receiving reports from the other station but this is a gamble. If calling a station on random, try to set your transmit frequency so that you hear your echoes on top of his echoes. This is easy if you can hear your own echoes. If not, do the best you can by looking at the calculated doppler shift of your own echoes and setting your transmit frequency accordingly.

Long ago, the so-called TMOR signal reporting system was used on EME. T meant traces of signal heard, M partial calls, O full calls, and R full calls plus report had been copied. These days the T and M are seldom used... most operators wait until they have copied complete calls before sending any report at all. For a valid contact, complete calls, signal report and acknowledgement must be received by both stations.

There are some rules, at least for scheduled contacts, on what should be sent during what part of a sequence. If transmitting calls only, you obviously just keep repeating the calls over and over: AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG. Putting a "de" between calls is not needed. If you are sending calls and a report, send the calls for the first 1.5 minutes and the report only for the last 30 seconds: AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG O O O O O. Once complete calls and report have been received, it comes down to acknowlegement and sending a report back. This is done with "Roger O's", for the entire 2 minute sequence: RO RO RO RO RO RO RO RO. And final rogers by sending R's for the entire 2 minutes: R R R R R R R R R R R R. Most operators also finish up with 73 or TNX 73 if time allows.

Having said all that, here is a sample QSO between AA8FG and N1BUG, arranged for 0900 utc, from the N1BUG perspective. Transmit sequences are in red, while receive sequences are in blue.

0900-02   AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG

0902-04

0904-06   AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG

0906-08          BUG                A       AA8F

0908-10   AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG

0910-12          8FG N1BUG AA8FG N1BUG AA8

0912-14   AA8FG N1BUG AA8FG N1BUG AA8FG N1BUG O O O O O O O O O O O O O O

0914-16           RO RO       O       RO RO RO RO RO RO RO

0916-18   R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

0918-20   73 73 73 73 TNX 73

Sometimes it's a lot easier; sometimes NOT; but you get the idea.

On random, it is generally best to give your call more than the other station's call, since he may be struggling to figure out who is calling. Here is a typical random QSO.

2300-01   CQ C        8FG AA8FG AA8FG         CQ CQ AA8FG AA8

2301-02   AA8FG N1BUG N1BUG N1BUG AA8FG N1BUG N1BUG N1BUG N1BUG

2302-03   QRZ QRZ QRZ QRZ AA8FG AA8FG QR                Z QRZ AA8FG

2303-04   AA8FG N1BUG N1BUG N1BUG AA8FG N1BUG N1BUG N1BUG N1BUG

2304-05   N1BUG N1     N1BUG AA8FG N1BUG     UG AA8FG O O O O O O

2305-06   AA8FG N1BUG RO RO RO RO RO RO RO RO RO RO RO RO RO RO RO

2306-07   N1BUG AA8        R R R R R R       R R    R        R R R R R R R R R

2307-08   73 73 73 73 TNX 73 TNX 73 TNX 73 73 73 73 AA8FG N1BUG SK SK SK

 When and where to listen

If you want to try listening for EME signals, you really should get a moon tracking program that helps you identify the best times, or check into the EME Net (see following section) for advice on when to listen or to make a sked with a big station. If you can elevate the antennas, try listening when the moon is visible in Europe (if you live in North America) and the sky temperature is below 400 degrees K, and preferably when the moon is near perigee. There is usually more activity on weekends, and it helps if the moon is fairly well to the north (Declination positive, or above the equator). All of this information is given by the various moon tracking programs.

If you cannot elevate the antenna, try listening at your moonrise (assuming you live in North America). You can also try listening on moonset, but there will probably be less activity then.



Another way to spot the good weekends is to download the EME scheduling database and the program to view it. You can get these from AF9Y's web site. Once you get the program (SKD81a) and the latest data file (VHFSCHED.SKD),  you will be able to see when most stations are running skeds. Those will be the best times to listen or make a sked of your own. Under the Utilities menu, the program has an option to View skeds chronologically. Try that. By the way, you can also view the skeds from the VHFSCHED.SKD file by using Z-Track moon tracking and scheduling software.

 Scheduling and Information Resources

The 432 and Above EME Net meets Saturday and Sunday on 14.345 at approximately 1600 utc, followed by the 2 Meter EME Net at approximtely 1700 utc. Note: times are one hour earlier when Daylight Savings Time is in effect.

There is an Internet mailing list for discussions about EME and scheduling. To subsribe, see http://www.nlsa.com/help/moon-net-help.html.

 

 Links to some interesting info on EME equipment and other stuff

LINKW5UN Home Page . Another "Getting Started in EME" tutorial. An inexpensive antenna and phasing lines for EME, a preamp, etc. Also a good place to start looking for a first EME QSO if you have a small station. Check out Dave's "Mighty Big Array" (which proves that everything really is bigger in Texas)!

LINK Equipment For VHF DX. Information on polarization switching and other stuff from SM5BSZ. Leif showed us all just how much can be gained from switchable polarization! Much of the stuff here is very advanced.

LINK VE3KH Amateur Radio Web Site. More info on X-yagi polarization switching and other goodies.

LINK EME, SETI, Radio Astronomy and DSP for Radio Amateurs. Lots of info on EME, etc.

LINK AF9Y EME and Weak Signal Page. Mike's FFTDSP program (check it out!) and more.

 

 Some examples of 2 meter EME Signals

Here are some recordings of actual EME signals.

AUDIO A typical 144 MHz EME singnal with no audio filtering. Very little QSB on this one. Can you identify the station? This signal isn't too strong, but most experienced EME'rs can easily copy it. If you can't, don't worry: it takes lots of practice.
Provided by AF9Y

AUDIO A 144 MHz EME signal with narrow filter. Notice the QSB. This is quite typical of EME signals.
Provided by VE7BQH

 EME Frequently Asked Questions

The following is based on actual questions I have received since I created this page. I will continually add new questions and answers, as they come in. Have one not on the list yet? Email it to me!

Antennas
Preamps
Miscellaneous

 Antennas
Q. I can't elevate my antenna off the horizon. Can I still work EME?
A. Yes! This just means you are limited to a 30 to 60 minute window when the moon is rising or setting. You can still work a lot of stations.

 Preamps
Q. What is a good preamp to use for EME?
A. Use a GaAsFET with a noise figure under 0.5 dB if at all possible. You can work the big stations with less, however.

Q. Should I mount the preamp at the antenna?
A. When you get serious about EME, Yes. This will significantly improve your station's ability to detect very weak signals. In the shack is OK to start or for very casual EME operating.

Q. Who sells good preamps?
A. Here are several sources to check out. These are not sorted in any particular order.
LNA Technology has preamps (including high level cavity types), power dividers, and other accessories.
Landwehr has some for 144 and 432 MHz bands. The link is to Qualitas Radio, a UK distributor.
DB6NT (Kuhne) makes some very low noise preamps for all bands, and many other items of interest.
RF Ham sells an excellent line of miComm preamps.
DownEast Microwave sells preamps and preamp kits for all bands. For EME, check their "ULNA" series.
Advanced Receiver Research.
Hamtronics if price is the main concern and you can live without the best noise figure (probably fine on 6m and OK on 2m).
G3WDG kits for 13 and 23 cm.
WD5AGO (contact him and ask...)

 Miscellaneous
Q. I can't hear my own echoes. Will anybody else hear me?
A. Yes. The stations with big antennas will hear you even if you can't hear your own echoes.

Q. I tried to work a station and he didn't hear me (or I didn't hear him). Does this mean my station isn't good enough to work EME?
A. No! EME conditions vary a lot. Even the big stations don't always hear each other so well. Just try again!

[....just a fancy line....]

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