Job Geheniau's Radio Telescope
ABOUT
My name is Job Geheniau, 56 years old and I live in the Netherlands.
After throwing in the towel a few years ago regarding visual perception and recording, I have been pleasantly surprised with the possibilities of radio astronomy.
As a young student I was sometimes involved with the "illegal" 3-meter band, building transmitters and using them and I studied electrical engineering for a while. So I have some knowledge of things such as transmitters, receivers, antennas, etc. For example, in addition to radio astronomy, I started receiving weather satellites on the 2-meter band - 137 MHz (NOOA, MeteorM2 and Fengyun 3B) and the space station ISS with its ISS SSTV broadcasts with a self-built QFH antenna.
Then I started to try to receive Meteor Scatter (ionization traces) on the 2-meter and 6-meter band. 143 MHz and 50 MHz. For this I use two 4 elements Yagi Antennas. These capture the reflection of a meteor ionization trace from 2 well-known beacons, namely GRAVES (> 400 KW) in France and BRAMS/Dourbes in Belgium (150 Watt). I won't go into too much detail about that, but a nice extra is that it is possible to receive an EME (Earth, Moon, Earth) reflection from the GRAVES transmitter. GRAVES emits pulses of about 2 seconds and you can clearly see the pulses and the associated Doppler effect in the spectrum because the moon moves in the recorded time. In the Figure 6 you can see the moon reflective, some planes (oblique lines) and some small meteor ionization traces (vertical lines).
But after that, a long-awaited dream came true. The purchase of a 1.5-meter RF Hamdesign radio dish with rotator.
I started building that "small" radio telescope. My goal was to make everything work automatically, remotely and autonomously as much as possible (while I'm writing this article on vacation, I can view the status of the telescope online and start an observation via the laptop). I chose a 1.5-meter telescope from RF Hamdesign (a kit) because of the limited space on my roof. The receiver (Feed) is a so-called can feed with the 1420 MHz probe.
Since I am going to control everything remotely, I decided to add an Azimuth-Elevation rotator (SPX-02 from RF-Hamdesign). This rotor can track the object with an accuracy of 0.5 degrees. The more expensive one can track at 0.1 degrees. Then directly behind the feed (because the signal is extremely weak) the amplifiers and a bandpass filter must be placed. After a lot of experiments, I built the following construction:
A LNA (Low Noise Amplifier) from Mini Circuits (ZX60-P33ULN +), then a bandpass filter to filter out interference (1300-1700 MHz) and then a second LNA from Mini Circuits.
All this fed by a second bias-tee (which supplies the LNA's with voltage without disturbing the signal). The Mini Circuits LNA's operate on 3.3 volts so there is a second bias-tee with LM117 voltage regulator from + 5 Volt to +3.3 Volt.
Via a 15-meter Coax cable, the signal enters the laptop to a RTL-SDR or Airpsy Mini (a USB radio receiver).
Initially, I set up everything on the roof of my home in The Hague. It was a difficult job to walk with concrete blocks with a backpack over a roof edge of 12-meters high and 15-cm wide to reinforce the whole buildup for heavy winds. Unfortunately, it soon became apparent that the interference (RFI - Radio Frequency Interference) was so high that observations were impossible and I had to remove the whole construction again!
Fortunately, my parents (80 years old) were willing to give up a place on their barn in the Haarlemmermeer for my dish (my father continues to call it ‘Het Vergiet’ ‘The Colander’).
The entire radio telescope and software can be operated fully automatically via Teamviewer/Chrome Remote and a resettable Internet repeater via WiFi. The computer can also be reset remotely, with an autostart when the power is switched on. To be less troubled by ground radiation and to improve the sensitivity, I managed to increase the dish diameter to about 1.9-meters with pieces of mesh.
