APPENDIX B - Constructing a simple Power Divider & Phasing Harness
APPENDIX C - Xmit/Rcve Antenna and Preamp Coax Switching
After the ARRL published an article about my Texas MBA (Mighty Big Antenna) in The January 1989 issue of QST, I was deluged with requests for infor- mation by hams who wanted to try eme, but who had no idea of how to get started. I found that I was spending much of my time explaining eme requirements and procedures over and over. It occurred to me that some sort of written instruction containing all the basic requirements would be timely and time saving. This primer is the result.If you read and follow the instructions given here, you should be able to determine what station improvements you will need to make,and what operating procedures you will need to learned in order to start hearing signals, and making QSO's on two meter EME.
The first, and most important piece of equipment needed for eme work is an adequate antenna system. By adequate, I mean one that is properly designed, constructed, and phased (when using more than a single antenna) to yield the gain required for successful eme communications. My experience has shown that the minimum gain of an eme antenna should be no less than 13 db greater than a dipole. With this gain, you will be able to hear eme signals on occasion when pointing toward the rising or setting moon (if there is activity, of course). With 150 watts or more of power, and advanced scheduling, you may even be able to work some of the very large eme stations. To be capable of making routine QSO's you will need an antenna system with 20 dbd or more of gain. W5UN has worked a couple of stations who were using a single long boom antenna and running less than 50 watts, so it can be done. I made one such contact with W2RS who answered my CQ. At the time W2RS was running 50 watts into a single Cushcraft 32-19 antenna.
Many different types of antennas are being used for eme work. The most popular type among active EME'ers seems to be the long boom Yagi. By long boom, I mean boom lengths greater than 4 wavelengths (about 27 feet). Some of these are sold commercially, and include the KLM 17LBX, Cushcraft 42-18XL, M2 Enterprise 2M5wl, the F9FT Yagi, and the K5GW Yagi. All of these are being used today by stations who are sucessfully making eme contacts. Other stations, such as VE7BQH are using collinear arrays. One station, VK5MC even uses a fixed rhombic antenna with great success. Which ever antenna is used, the key to success is that it be working at its peak performance level. That means that care must be taken with construction, feeding, and phasing.
If you find a commercial antenna too costly, you may want to consider building your own. A long boom quagi, with the necessary gain for eme work, can be home brewed inexpensively. This is an updated design of the quagi antenna first used by W5UN (I had 16 of them in a phased array). If you build and properly install four of these quagi's, you will be able to make routine eme qso's with 500 watts or more of power delivered to the antenna system.
It is very possible that you will hear eme signals from the larger stations if you have a circularly polarized antenna (such as those commonly used for satellite work). However, most such antennas lack sufficient gain to get your signal to the moon and back with enough strength for others to hear, unless you are running very high power (probably 1000 watts are more into the circularly polarized antenna would be required for you to be heard). Such antennas should not be considered for eme work.
RECEIVERS & PREAMPS
For serious eme work, your receiver's front end noise figure should be kept below 2 db. Typical commercial grade 2 meter multi-mode rigs have front end noise figures that are worse than 5 or 6 db; not so good!. If your receiver's front end is not so hot, do not despair, a good low noise preamplifier between your antenna and your receiver will correct this deficiency. A good preamp is relatively easy to built. A preamp that works best is one using a GaAsFET device (such as the MGF1402). The preamp should be mounted as close to the antenna as possible, so that feedline losses will not degrade the receiving system noise figure (feedline loss between antenna and preamp is directly added as noise). Many of the solid state "brick" amplifiers have preamps installed in them. While these preamps are usually not the best performers, they are often good enough to let you hear the larger eme stations when eme conditions are good.
Preamplifiers that use bipolar (emitter-base-collector) transistors should be avoided. Even though some such preamps can yield noise figures less than 1 db, they are highly susceptible to intermodulation problems, and can cause "birdies" to appear all over the 2 meter band when used in locations where there is a lot of transmitted rf in the VHF bands. These preamps may work ok if you happen to live on a south sea island where there is no other RF signals, otherwise, avoid them.
Any preamp placed ahead of the receiver (preferably as close to the antenna as possible) must be protected from "burnout" when transmitting by some type of protective relay switching circuit. See Appendix C for circuit diagram and construction details for a suitable circuit.
COAX FEED & PHASING
Although feedline losses can be overcome on receiving by installing a preamp at the antenna, these losses will still reduce the power leaving the amplifier before it reaches the antenna. Power reaching the antenna is what counts in EME work. For example, 100 feet of regular RG8 coax will have nearly 3 db of loss on 2 meters. That means if you start with 100 watts output from your amplifier, only 50 watts will show up at your antenna. Use the shortest length of high quality, low loss coax that you can afford. Try to keep losses to less than 1 db. As a rule of thumb, Belden 9913 is ok for lengths up to 50 feet long. 1/2 inch hard-line is ok up to 75 feet. 3/4 inch hardline will work to 175 feet. RG58 coax is totally unacceptable, and should not be used at all.
Be careful about installing and using coaxial connectors. Losses can be accentuated and swr problems can result from poorly installed connectors Connectors often act as a point of entry for water condensation. Be sure to properly seal any connectors that are installed outdoors. Better yet, avoid installing any outdoor connectors, if possible.
If you are going to use more than one antenna (two, four, or more Yagi's are typical installations for obtaining higher gain in eme work) you will need to construct a phasing harness from coaxial (or open wire type feed) cable. This can be another source of possible losses if not carefully constructed. A well constructed coax phasing-harness with power divider is shown in Appendix B for a 4-Yagi antenna array. Notice that no connectors are used for the harness. Be sure to seal all the soldered connections. This can be done by wrapping open connections using vinyl tape, and then overcoating the tape with PVC pipe cement. Better yet, use non-contaminating Silicon Rubber Sealer (available from GE or DOW Corning). Do not use the commonly available sealer that is found at hardware or variety stores. This type develops acetic acid while curing, which causes copper to corrode.
The minimun power that should be considered for two meter eme is about 150 watts. Some commercially available solid state brick amplifiers can produce this. The output of two such brick amplifiers could be combined to double the power output. This can be tricky, so if you plan to try this, get the proper information on how to do it. For the more serious eme effort, power of 500 watts output or more is recommended. Commercial amplifiers are available that will give power outputs of 1KW and more. Many eme operators build their own power amplifiers. The 2 meter W6PO 8877 amplifier has been built by many, and performs with exceptional results. This is the amplifier used by W5UN. Information on how to construct the 8877 kW amplifier is shown in Appendix D. The ARRL handbook is a good reference for home construction of other amplifiers. Kits are also available at times. Check the classified advertisement section of QST or other ham magazines for kit suppliers or for used amplifiers.
As I said before, you do not need high power to listen for eme signals. Listening is a good place to start your eme experience. Let me emphasize again that you may be able to make a contact with the larger moonbounce stations, even if you are running modest power (100 watts output, or so). Many have done this judging by the great number of small stations that I have worked from W5UN.
EME operation on 2 meters is primarily done on cw. Signals are very weak echos reflected from the moon's surface. Signals are usually at the noise level, or even buried beneath the noise, ocasionally rising above the noise for brief periods. Hard listening and mental concentration is required to pull the signals out and identify what is being sent. Let me repeat for emphasis; To have the best chance to hear eme signals you need a receiver with a reasonably low noise front end. Most commercial receivers are not good enough, but a relatively low cost preamplifier can fix that. Your well designed antenna must be pointed at the moon. In most locations, ground gain can often give some signal enhancement when the rising or settig moon is below 12 degrees of elevation. This would be the best time for listening if you are using a small antenna. It is the only time to listen if you cannot elevate your antenna. Moderate eme activity often occurs on weekends when the moon is in a favorable sky position. Activity peaks when the moon is within common view of both Europe and North America. Random activity can be heard between 144.006 mhz and 144.035 mhz. Schedules are run between 144.030 mhz and 144.120 mhz. You must dig signals out from between the externally generated "birdies" that you will inevitibly hear in that portion of the band. Single sideband eme voice signals are sometimes (but rarely) heard around 144.115 mhz. W5UN usually operates cw on 144.028 mhz during favorable conditions My operation occurs mostly on weekends, when the moon is near perigee, and before moonset has occured in Europe. This occurs one (or two, at most) weekends per month. W5UN sometimes operates during mid-week also. When W5UN is active, you may hear me calling CQ or occasionally working another station.
WHAT AND WHEN TO TRANSMIT
Most 2 meter eme operating by smaller equipped stations is based on pre-arranged schedules and use the two-minute xmit/rcve sequence interval. The two minute xmit/rcve sequence works as follows: If you are attempting to QSO a station that is east of you, that station is called the eastern station. Conversly, you will be west of him, so you will be the western station. The eastern station begins transmitting at the beginning of the hour, and will transmit for 2 minutes. You will be listening. Then at two minutes past the hour, you will begin transmitting, and the eastern station will be listening. This 2-minute sequence will continue until the schedule is completed, or schedule time runs out. Schedules do not necessarily need to begin at the top of the hour, but can begin at any time agreed to by the scheduling stations. However, the two-minute sequence timing intervals are referenced to the beginning of the hour to avoid confusion.
The only information required for a sucessful 2 meter eme qso is the reception of calls, O's, RO's, and R's by both parties. 73's are often sent, but are optional. Here is an example of a valid QSO: W4ZD in Florida and ZD8MB on Ascention Island have a one-hour schedule starting at 1000 Z. ZD8MB is the eastern station. During the first two Minutes ZD8MB will send calls over and over for the full two minutes (W4ZD de ZD8MB). W4ZD will begin transmitting at 1002 Z. If he heard calls he will send ZD8MB de W4ZD for the first 1-1/2 minutes and O's for the last 1/2 minute. If W4ZD did not hear both calls, he will send only calls for the full 2 minutes. This continues until either station has heard both calls and O. Once an O is heard, RO is sent in response for the full 2 minutes. Once RO's have been heard, by one of the stations, that station responds with R's for the full 2 minutes. The station copying RO's has received sufficient information for the qso. When the station transmitting RO's hears an R, he has received sufficient information, and the qso is essentially complete. Most stations, upon hearing R's will respond with 73's to let the other station know that R's have been received. Here is an example of how a qso might go during the entire schedule period.
|Time-UCT||First 1-1/2 Min.||Last 1/2 Min.||Comments|
|0000 - 0002||W4ZD de ZD8MB||W4ZD de ZD8MB||Initial transmission|
|0002 - 0004||ZD8MB de W4ZD||ZD8MB de W4ZD||Nothing hrd yet by W4ZD|
|>||0004 - 0006||W4ZD de ZD8MB||0 0 0 0 0||ZB8MB heard calls from ZD|
|1006 - 1008||ZDBMB de W4ZD||ZD8MB de W4ZD||W4ZD didn't hear calls|
|1008 - 1010||W4ZD de ZD8MB||0 0 0 0 0||ZD8MB still needs RO's|
|1010 - 1012||ZD8MB de W4ZD||ZD8MB de W4ZD||W4ZD got O's but not calls|
|1012 - 1014||W4ZD de ZD8MB||0 0 0 0 0||ZD8MB waiting for RO's|
|1014 - 1016||RO RO RO RO||RO RO RO RO||W4ZD got calls and O's|
|1016 - 1018||W4ZD de ZD8MB||0 0 0 0 0||ZD8MB didn't hr the RO's|
|1018 - 1020||RO RO RO RO||RO RO RO RO||W4ZD waiting for R's|
|1020 - 1022||R R R R R||R R R R R||ZD8MB heard the RO's|
|1022 - 1024||R R R R R||73 73 73||W4ZD completes the QSO|
A printed out time sequence schedule sheet is handy if you are new at this. I use one to help me remember who should be transmitting and who should be listening at any time during a schedule. This sheet is especially helpful in determining who should start transmitting first whenever a schedule is set up to start at some time other than at the beginning of the hour. Whenever I get confused about if I should be transmitting or receiving, a quick reference to the sheet will immediately clear it up.
You might read in some of the early eme references where M's and T's are used. M was meant to let a station know that bits of a call was being copied, but not enough to respond with O's. T's were to be sent if something was heard in the noise, but no characters could be distinguished. M's and T's are no longer used by 2 meter eme operators. I have found that they can cause confusion rather than help, especially when both stations are having a difficult time hearing each other. As a general rule M's and T's should not be used.
ABOUT RANDOM QSO'S
Having said all the above about 2 minute sequences, you will find that a lot of random activity is conducted using one minute sequences. In fact, nearly all random QSO's made by W5UN are one minute sequence based. The reasoning here is that if stations are hearing each other well enough to copy random calls, then the additional time is not needed to get the required information passed.
Random activity is quite a challenge for the smaller equipped station. However, by answering the CQ's of larger stations who are often transmitting on the bottom 30 khz of 2 meters, it is possible to make QSO's this way. It is a known fact that the signal level of a scheduled station can be several db less than that of the weakest identifiable random calling station, and still be worked. One reason for this is that a listening operator will mentally fill in the missing parts of a very weak calling station because he knows what the call is already. A second reason is that when one knows that a certain station will be there calling on schedule, he will shift his ears (and brain) into a more focused filtering mode in order to dig that station out of the noise. For this reason, very small equipped stations are urged to make advanced schedules whenever possible. However, don't give up on answering random cq's, because you never know unless you try. It can be a very satisfying experience (or frustrating if you are never heard).
A good place to get information on the air about eme operation
is the 2 meter eme net. This net meets every Saturday and Sunday on 14.345
mhz. USB at 1600 UTC during summer daylight savings time, and 1700 UTC
at other times. VE7BQH normally chairs this net. You are welcome and encouraged
to check in. Schedules and eme operating information is exchanged on this
The EME Directory
The EME Directory is a database of known 2 meter eme stations which contains detailed information about those stations. This database is managed by WB5LBT, and is available from WB5LBT as well as from several internet on-line sites. Software that will display the EME Directory data includes PCF and SKYMOON, as well as some others I'm not crrently familiar with.
Tracking And Operating Aids
There are several computer programs available that will assist in your eme A basic moon tracking program called MoonBrat can be downloaded from this site. Advanced and more powerful tracking programs that are available include Skymoon, Nova4, and The VK3UN EME Planner. Take a look at the Skymoon page to see typical capabilities of Skymoon, as well as the other programs.
Besides performing as an excellent keyboard cw generation program, Cwkey4 is also a program that will track the moon, steer your antenna, and do logging chores.
Other helpful operating software
FFTDSP42 is operating software which does real time signal detection, and shows a visual trace of the signal on your computer's screen. This program, which does Fast Fourier Transformation of the signal, will not decipher what is being sent, but it will let you "see" a station's trace if the signal is in your receiver's audio bandpass. I can see traces of very weak signals even when I cannot hear the signal with my ear, much less hearing what they are sending. FFTDSP42 requires a compatable sound card, and is available from AF9Y.
DSP Blaster is a computer based software filter program that runs real-time. It including a very good noise reduction filter that seems to work well for eme signals. DSP Blaster does require a sound card from Creative Labs that uses a vibra sound chip. (no substitute sound card will work). Pentium type processors work best for full filtering capability. DSP Blaster is available from Brian Beasley, K6STI.
Sequence Scheduling Sheet
Use your browser's print-out capability to grab and print out the time sequence Sequence Scheduling Sheet. You will find it to be an invaluable aid for helping you to stay on the correct xmit/rcve sequence during your eme schedules. You will probably want to have a fresh, clean new copy for each and every schedule.
I hope that you have found this EME Primer to be of assistance to you. I look forward to working you on 2-meter eme soon.