VE7TIL 2m EME Station
Last update: February 22, 2007
A couple of years ago Steve, VE7SL planted the seed in my mind to get on 2m EME. With the seed planted I went about gathering the parts to build a basic yet effective EME system. What follows is a brief description of what I came up with.
The station consists of the following major subcomponents:
· Azimuth control was done using an old AR-40 type rotor, which was rebuilt.
· Elevation control was done using an old satellite dish actuator arm also restored and a piece of 1 ½” nominal AL pipe with a piece of 1 ½” O.D. tubing inserted thought the pipe to provide a hinge that required no machining. Grease nipples where installed to allow for periodic lubrication.
The following are some details of the construction of the station.
The images below depict the element mounting method I used to construct my variant of the DK7ZB 3.3m boom narrow bandwidth 2m yagi.
I used common marine electrical enclosures to support the driven elements. Note: If you assemble a stacked array, be careful of how the driven elements are phased! I spent days trying to understand why I could not be heard by anyone and my SWR was normal! The elements should all be the same.
Early successful attempts where conducted with a single 7 element DK7ZB yagi. I was only successful with the largest EME stations such as W5UN, KB8RQ and RU1AA. I worked W5UN with 50W and a single 7-element DK7ZB yagi.
However, I soon realized that I needed much more gain but what can 3dB really do?
I experimented with the above 2x7 array for a couple of months in what turned out to be the worst winter in living memory here in Vancouver, BC. Normally we get a lot of rain and not much else. This year we had high winds and heavy snow! Of course the snow caused chaos to the array! The 2x7 system worked very well and allowed me to work fairly small stations and 58 initials in 3 months… It planted a seed in my mind that a very portable and effective EME system could be made from a crossed pair of 7 element DK7ZBs as often what failed me during QSO attempts was Faraday lock out… A switchless combiner as described by SM5BSZ may be the answer for phasing…
Be careful not to place the balun cable too close to the boom or the following will certainly occur at EME power levels!!
The H-frame was first to be placed on the small 20’ tower…
Prior to using anything on the air I wanted to understand the requirements of JT65 and ensure my equipment and systems where up to the task. Here are the test reports for the various components I tested. Early in my experiments I used a separate TX and RX but the principles in the following remain the same if you choose to do these tests on your station equipment…
Once I completed the station, I of course pointed my antenna at the moon and tried to work as much DX as possible! But there are many days in the month when the moon is in a very uncooperative position in the sky… This led me to test the RX system by attempting to use the Sun as a noise source.
The Yellow circles indicate noise the correlated to snow fall during these tests. The Red circles indicate the Sun and Sagittarius A, AKA the center of our galaxy! The time of year I did this test happened to be when the Sun and Sagittarius where together in the sky. The Blue circle is me up the band on 2m FM.
About a month later I ran the same test using the completed 4x7 array and was able to distinguish both the Sun and Sagittarius A as distinct objects in the sky. Sagittarius being the early bigger hump and the Sun the smaller later one…
The next task was to explore the local noise field here in urban Vancouver, BC. I sweep 360 degrees at 0 degrees elevation and produced the following plot of the noise all around me.
What came as a surprise was the noise peaks corresponded to large objects on my horizon, namely mountains and large buildings on the East side of the plot. The really big peaks are my house and a couple of neighbours to my SW, W and NW.
I then asked Steve, VE7SL to provide a weak signal from his QTH in CN88 and plotted the following:
Interestingly the plot of Steve’s signal shows a correlation between the known locations of the large objects on my horizon and peaks in his signal. The reverse is true when the antenna passes through the nearby houses blocking the path to Steve’s QTH which is on a bearing of about 200 degrees.