Do you have a directional antenna, a 2m SSB transceiver with 50 W
output and a PC?
If your answer is YES then, believe it or not, you are capable of
making a QSO with EA6VQ (and other stations) using the Moon as a reflector.
Please continue reading this page and you will discover a new world of DX
communications, where you can work stations all around the world on 144 MHz.
Disclaimer: 2m EME communications can be addictive
and if you try them you are likely to get side effects, like losing interest
in other hobbies, in other bands and in other DX modes. If you don't want to take this risk you had better
leave this page right now.
EME with a single Yagi and 50 W?
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 sourceforge.
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:
Use 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 or
BktTimeSync programs 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.
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 or in LiveCQ
on 144 MHz,. 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.
If you have some doubt or you need any additional information don't
hesitate to send
me an E-Mail
A Romanian translation of this JT65B / WSJT tutorial, provided by YO6XK,
is available here.
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