EME with a single Yagi and 50 W? Some setup to Try
There is still some confusion about Moon Bounce operation and the station requirements for making a QSO in the VHF bands using the Moon as a reflector. Might be you have read in the past that only very large stations with four antenna arrays and Kw amplifiers (and skilled CW operators) were capable of working via EME (Earth-Moon-Earth). This was true till 2002, but nowadays thanks to the JT65B digital mode provided by the WSJT program, any station having an 2m. SSB transceiver capable of delivering 50 W and a directional antenna can make successful contacts via EME. And furthermore, no CW knowledge is required!
But, I can’t elevate the antenna to track the moon…
In order to make an EME QSO, the most important requirement is (obviously) that both stations can see the Moon simultaneously (what is called “to have a common window”). If you have a typical tropo/MS antenna you are likely not to be capable of elevating it, but YOU STILL CAN make EME contacts when the moon is near the horizon.
A single Yagi antenna pointing to the horizon normally allows to work EME till the Moon is up to 15 or 18 degrees above the horizon. If you have a clear take off towards your moonrise/moonset this means about 90+90 minutes (3 hours) of possible operation every day!
Do I need a good preamplifier?
A preamplifier with a low noise figure, mounted as close to the antenna as possible is always a very good help, but it’s not strictly necessary to make your first contacts. The larger EME stations are normally using a lot of power and somehow this will compensate your little reception. You can always get a preamplifier later, when you decide it’s time to improve your reception.
You are only 7 steps away from making your first MoonBounce QSO! Keep reading…
Step 1. Get the WSJT free program
WSJT is a digital communications program written by K1JT and specially intended for weak signal communications in the VHF&up bands. It provides different modes adapted to different modes of propagation and bands. For 2m MoonBounce you will use the JT65B mode. You can download it from K1JT’s WEB site.
Once you have downloaded the setup program you will have to install it your PC. If you are familiar with installing Windows applications this will be very easy, as you simply have to accept the default options offered by the setup program, however if you want you can also have a look at the WSJT setup procedure.
Step 2. Connect the PC to the radio.
If you have already worked some kind of digital communications (RTTY, Packet, PSK-31,etc) you will possibly be able to use the same interface for the WSJT program, and you could skip this step.
If you have never connected your PC to the transceiver then you will need some kind of interface to connect them. If you can afford it the best is to buy a commercial interface, such as the RigBlaster (available at West Mountain Radio).
If you want to build your own interface, you will need to make the serial port cable from your computer be able to key the PTT line of your transmitter. You also must isolate and attenuate the audio from the computer sound card (Line output / Speaker), so it can be connected to the transmitter MIC input. Information on how to do this can be found in many places, but here you have two simple designs.
And finally, you will have to split the audio output from your receiver, and run an audio line over to your computer sound card (Line input / Mic). This will permit your computer to also hear your receiver, and process the signals coming in.
Step 3. Automatically synchronize the PC Time.
WSJT modes (and specially the JT65x) require of a very accurate PC time in order to achieve good results. So accurate that in fact it’s not enough to update the PC time manually. It’s necessary to update it automatically according to some reliable source.
The most common way to do it is through Internet by using a Time Synchronization program, such as Dimension 4 or Automachron, and configuring them to synchronize the time every 5 minutes or so.
It is important that you select one of the time servers that will provide accurate and reliable time corrections to your computer from your particular location and internet connection. You can verify that the time has been properly set within a half second, by listening to WWV and watching the seconds display on the Dimension 4 program screen. If the time server you select doesn’t seem to match WWV, or there seem to be corrections >.1 second when you repeatedly manually set the time with Dimension 4 or Automachron, try selecting a different time server from the optional list provided.
However, if you don’t have an Internet connection in your radio shack then you still have other alternatives to achieve an accurate PC time synchronization:
se the time signals broadcasted in LW and MW and a program like Radio Clock that keeps the PC time synchronized simply connecting the speaker output of the receiver to the line input of the PC sound card.
Use a GPS receiver connected to the PC and the free GPS Utility program to update the PC time with the GPS time.
Step 4. Run WSJT for the first time and Configure it
Configuring the WSJT options properly is important in order to make successful QSO, so please read carefully the page on configuration.
Step 5. Rig setup
Make sure your transmitter is set to USB position and that the receiver is set to the widest filter width. If you have bandpass adjustment on your receiver, make sure it is set to pass tones from 1200 Hz – 1800 Hz (usually by turning the bandpass off). In general you could leave the noise blanker active, but make sure you turn the AGC off. If your rig has a Mic. compressor or speech. processor button you should also activate it, to insure that you are sending each of the tones at full power.
Step 6. Program operation
You should definitively read the operating manual provided with the program as it covers almost all details you need to know, however you could also find interesting to watch the following visual examples of real JT65B EME QSO.
Get on the air
Now you are ready for your first WSJT EME QSO. However here there are some additional suggestions for you:
- Always make your first attempts arranging a “sked” with some of the bigger stations (8 Yagis or more). Please contact me and I will be pleased to calculate the most favourable date and time for trying a 2m EME QSO with you.
- Scanning the band looking for signals is not a very good idea. Only stations with large arrays can detect the weak EME signals by ear. You had better look for the frequency of the stations calling CQ, in the DX-Cluster or in the JT65 EME chat or in the ON4KST EME chat,. Then you can try to detect their signal and answer to their CQ.
- Don’t expect to hear the signals on the speaker or headphones. Although you could eventually listen to the signals of the most powerful stations, that won’t be the rule in JT65B EME operation. You should pay attention to the SpecJT waterfall display and you will see signals that are too weak to be heard by the human ear, but that could be neatly decoded by the program.
- Don’t give up if you don’t succeed in you first EME attempts. There are many factors affecting the Earth-Moon-Earth path and some of them are unpredictable. Often you will have to try several times till succeeding in a QSO.
- Don’t give up if you don’t get an answer in the first minutes. EME conditions change very quickly, mainly due to polarization changes, and quite often you will need up to 30 minutes to complete a QSO. Continue transmitting all you periods so that your partner station will have to chance to copy you when signal improves.
- Don’t get obsessed trying to detect your own echo off the Moon. If you have a single Yagi and a few hundred watts it would be really surprising that you could detect them. Even when you can’t detect your own signal after the reflection off the moon many other stations with larger antennas will be able to detect it, and that is the really important thing in order to achieve a QSO.