Tuesday, 8 August 2017


This blog is intended to show and describe my endeavor setting up, running and maintain a 70cm EME station.
I started by choosing design of antennas and my choice is a 25 element yagi from DG7YBN great designs and building amplifier and LNA.
The reason for this choice is the length of close to 6 m which is an easy available length of aluminum in Sweden and simulations shows a very clean and nice pattern and a direct 50 Ohms feed without any coaxial impedance transformer.
Like to build everything for my self and like the concept of isolated element through the boom so I went for 4 mm elements and plastic inserts from Theofils.

Amplifier was a KW of W6PQL design and some kit parts was ordered and assembled during spring and summer and for LNA I have a stock of ATF54143 and like the YU1AW design where the input is grounded and tuned.
Built 3 LNA's and the results are in the area of 0,34dB noise and 21dB gain which is fairly OK.
During summer 2016 I built 4 yagis and evaluated them and they behaves as simulated.
Measured some low sun noise but it was later found caused by interference from a local 70cm beacon.

Participated in the ARRL EME contest in 2016 using 2 of the DG7YBN yagis in both parts and managed 31 QSO in the contest and some 5 additional QSO's.
The setup was very temporary using a small speaker tripod only 8 meters from the house.
During the first part the weather was not good with high winds and a lot of rain detuning the antennas slightly.

The first part I started using an IC706 but realized quite quickly it was useless as the frequency drift at TX was huge even though I used a temperature stabilizing circuit for the reference oscillator.
Due to the drift at TX I could barely work HB9Q who was very strong and later after exchanging rig reported me on livecq as high as -9dB on JT.
Changed rig to an TS811E after the first night which was more or less absolutely stable after some 1 hour warm up time.
The first part I had no output power meter that could handle the power so I used some 400W or so to be safe.
In the second part I tried to increase output power but encountered some problems with the amplifier and could not use more then 700W or so.
But the amplifier had no cover and the antenna was mounted only 10 meters away from the station and I had some problems with feedback which is not really that strange.
Results was nevertheless very encouraging so I quickly decided to build 4 more antennas and use 8 of them, 4 wide and 2 high.
So this work is now on the way and everything is on track and the plan is to put the antennas up in less then a month from now.

Started by designing and building a 6 meter mast and rotators planned to use is a big RAK from alfaspid for azimutand an actuator homebuilt solution for elevation.
Horizontal boom for the antennas is a vårgårda mast with 200mm in side and 6m long.
Stacking distance for these antennas are 1,8 m side by side so I will use 5,4m of the horizontal boom.

All rotating will be controlled by a homebuilt interface based on the K3NG rotor interface.
It includes a complete stand alone system with GPS receiver to correct for time and position and real-time moon and sun tracking.
As I will use 4 antenna wide I need good resolution in azimuth direction and the RAK rotor only has 1 degree resolution so I modified it for a HH12 from DF1SR which is a 12 bit magnetic absolute encoder.
Will show more details later

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