Friday, March 31, 2017

W8TN's 2-M EME Project

My last post was about my grandsons digging the hole for my new tower.  Why do I need a new tower?  Well, I'm building a moonbounce (EME or Earth-Moon-Earth) station for 2-M and need a place to mount the antennas.  This project has been in the planning stages for over 3 years now.  About 14 months ago I started to get serious and placed the order for one antenna.  Delays in shipping that antenna led to me adding a second antenna to the order and the 2 antennas were received from England on July 5th last year.  I chose the InnovAntenna 13el 144MHz LFA yagis as about the longest I could reasonably put up at my QTH.  Each antenna has 16.12 dBi Gain at 144.100 MHz on an 8.003m (3.85 λ or 26.26 foot) boom.  Two of them spaced 4m apart horizontally should give 19.05 dBi (16.9 dBd) total gain. This amount of antenna gain coupled to a 1,000 watt amplifier should give me a modest moonbounce station using WSJT software.  I will, of course, be limited to a single polarity and thus subject to dealing with Faraday Rotation but I should be able to work dozens if not hundreds of stations off the moon.

Block Diagram of 2-M EME Station
One major reason for choosing the LFA (Loop Fed Array) antenna is that it has been specifically designed to reduce the amount of noise that is normally received off the back and sides of the antenna.  The tight, highly suppressed pattern and closed loop fed system ensure everything from rain static to man-made noise are heavily reduced.  This is pretty much an essential feature of an antenna that is trying to hear the super-weak signals being reflected back from the moon.  It has a really excellent G/T figure (-1.33dB @ 144.100MHz) showing it is hearing very little from the rear and sides of the antenna.

To the left you can see the current block diagram of my 2-M EME station.  It has evolved as this project has progressed.  Click on any photos to see a larger image.

I started out planning for an extremely simple configuration that would just allow me to make the occasional EME QSO.  But, as planning progressed, I kept adding features to make it the most efficient and productive station I could manage.  To that end, I added the EA4TX Antenna Controller that when connected to software on my computer will automatically keep the antennas always pointed at the moon without the need for me to manually adjust the rotors.  I then added the BG7TBL GPS Disciplined Oscillator that will take signals from the GPS satellites and produce a highly accurate 10 MHz reference signal for my Elecraft K3S to ensure it is precisely on frequency.  This is very important with WSJT signals so I felt this would be something that would remove the necessity of my needing to manually insure the frequency accuracy of the radio.

Everything else in the system was chosen to keep the signal losses as low as possible.  Toward that end the preamp will be located as near as possible to the antennas.  The preamp will be directly connected to the T/R relay with a right-angle, double-male N-connector.  All control lines will be shielded.  All computer lines will have ferrites installed on them.  Low loss cables will be used throughout the system including 7/8-inch Heliax for the TX feedline.  The antennas are mounted right outside the shack to keep feedline losses to a minimum.  Using just two antennas is not going to make me a Big Gun.  But, if I can make those two antennas and the rest of the station perform to their maximum ability, I will do well.

I then decided to add the FUNcube Dongle to the system to allow me to see all the stations which I am able to hear who are bouncing off the moon at any particular time without the need to tune around for them or set schedules to work them!  Unlike HF, you usually can not "hear" the signals from the moon but the computer can.  However, it needs for you to be pretty close to the frequency of the signal in order for the computer to decode it.  The FUNcube Dongle is a SDR (Software Defined Radio) just the size of a USB Thumb Drive.  It can listen to a range of frequencies and decode (using the MAP65 software) all the stations in that range of frequencies at once.  You can think of it as acting like the CW Skimmer of moonbounce.  On the right you can see an image of one of the output screens in MAP65 when I ran it and used a sample file for testing.  You can see that it shows the frequency of each station along with what they were transmitting.  I am so excited to give this a try on real live EME signals!

One other very important part of this 2-M EME station is a good low-noise preamp.  To take full advantage of that item it needs to be mounted as close to the antennas as possible.  I purchased a couple of these preamps from WA2ODO and on the left you can see the Noise Figure Meter printout from the best of these two preamps.  Putting such a low-noise preamp right at the antennas will help to keep the system noise figure as low as possible.

As I continue to progress with this project I will Post articles here on my Blog about various aspects of what I'm doing.  Hopefully, before long I will be able to post the images of my first EME QSO's in a LONG time.  I was on 2-M moonbounce back in the 1980's but only made about a half dozen QSO's with CW.  It was huge fun but I'm expecting this new incarnation to be an order of magnitude better!

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