Amateur Radio Station for 10 GHz EME and Radioastronomy

0. Introduction

The aim of this contribution is to describe the design, the construction and the evaluation of a radio station with a frequency of 10 GHz which is capable of Earth-Moon-Earth communication (EME) and which can be used for Radio Astronomy also.

The problems can be structured into the areas

1. The mount
2. The antenna
3. The electronic part
4. The evaluation of the station

Since the signals from the moon are very weak at this high frequency you have to examine all the details very carefully and to fight for every fraction of a Dezibel (dB).

Beeing engaged with amateur radio for 50 years and with astronomy for more than 10 years we started with an existing equipment. The evaluation showed that the existing equipment was not very well suited for this task. We will explain the pros and cons for each piece of equipment in detail in the following.

1.The Mount

We started with an astronomical mount ALT5-ADN which is capable of an instrumental load of 50 kg - see figure 1. Due to some restrictions for a fixed installation we decided to operate the equipment in a "portable" way.

Fig.1 Polar mount ALT5-ADN

1.1 The initial construction

With a weight of the dish and the electronics of about 25 kg you have to counterbalance the declination axis in this configuration with about 17 kg (see the lower right part of the picture). This gives you an instrumental load of 42 kg which is near the limit of the mount. This instrumental load has to be counterbalanced in the right ascension  axis, as well (see the left part of the picture).

1.2 The Pros and Cons

The Pros: it works! The accuracy of the mount is about 20 arcseconds! It can be recommended for frequencies of 10 GHz and above when we have very narrow beam angles of < 0,5 degrees and the equipment is not to heavy. A good polar alignment provided it runs well for a long time without a lot of care from your side. If you have a small controller for the mount you even dont need a computer. It may be controlled by a computer with a program like "The Sky 6", of course.

The Cons: the total weight of the equipment is about 120 kg - not very portable. If the moon passes the meridian you have to perform a meridian flip (rotate both axes by 180 °). So you cant put the equipment on a roof for remote operation. The polarization changes continuously if you use LP (Linear Polarization) - you have to use CP (Circular Polarization). The mount is very sensitive about changes of the load.

1.3 The final construction

As we aimed for a solid dish of 2,4 m diameter which weights about 60 kg we decided to change to an AZ/EL-Mount from SPID (see figure 2).

Fig. 2 Mount for antenna loads up to 100 kg

A counterweigt for the EL-axis is not really necessary but releaves the gear. The accuracy of this equipment is 360 arcsec (0,1°) with suitable encoders.
It can be operated remotely on a roof and can be controlled by a computer.
The LP orientation remains fixed when you move the antenna. The total weight of the equipment is about 60 kg - half of the weight of the polar mount.

This contribution will be continued for the chapters 2, 3 and 4.

Jochem
DK2FT