Experiments with receiving images from Satellites
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The first item I needed to receive weather maps from the weather satelites in the 137 to 138 MHz band was a suitable antenna. Web searches provided me with a lot of examples, some of witch were quite complex, others looked too simple to be of any use. After reading a few articles I decided to make a crossed dipole antenn for 137 MHZ.
CROSSED DIPOLE ANTENNA FOR SATELLITE RECEPTION
A simple antenna for receiving satellite images from the 137 MHz band is the crossed dipole or turnstile antenna, it can be constructed at home without to many problems. Bear in mind this antenna is for 137 MHz, if you want to make one to monitor the packet transmissions from the international space station on 145.800 MHz, you will have to scale it accordingly, the driven elements now become about 48.5 cm, instead of 51.5 cm. The phasing (50 ohm cable ) could be left out if the antenna is just for receiving, or the cable length to the TCVR is short.
1) Make the matching loop out of 50 ohm coax and the phasing loop out of 75 ohm coax - see fig 3 for details.
2) Arrange the two loops and the 75 ohm cable to connect to your receiver as shown in fig 4 - connect together using plastic tie clips.
3) Drill four holes in a plastic box. The box can be about 4" x 3" to take the 4 antenna elements. I used 13 mm diameter aluminium tubing. Make sure that the elements sit flush with the bottom or inside of the box. Also drill a hole in the top centre of the box to take the screw to hold the box to the supporting pole - a 3/4" or 1" piece of dowel about 3 - 4 feet long will do as the support. see fig 5 / fig 2 for details.
4) Drill a hole about 3/4" from the end of each antenna element to take a self tapping screw to hold the solder lug - put the 4 antenna elements through the holes in the plastic box, the ends resting up against the supporting pole Now araldite the aluminium tubes into place ( any other epoxy glue will also do ) be quite liberal with the araldite - but don't get it onto the solder lugs. see fig 6
5) Now solder the cables fig4 to the relevant solder lugs on the elements fig 6.tape the loops and the connecting cable to the supporting pole. Seal the ends of the coax cable with more araldite. Put a suitable connector on the end of the lead to your receiver - mount the antenna on a mast outside or even in the house loft space.
My first experiment used a old Ham Radio Action project as the receiver. This must date back fourty years at least and it was not satisfactory. I then found two DVBt dongles I experimented with several years ago and these were much more stable and easier to tune. I am still experimenting with software.
Power injector for DVBt dongle
The antenna is quite a distance away from the shack so I have added an old television booster on the cable on it's way from the shed on the block to the shack. To supply 12 Volt power to this device I have used a power injector. The one that came with the booster was not to my likeing so I made one in a small dicast box and included an ON/OFF switch. I have made one with PAL connectors for the dongle and another with BNC connectors in case I wish to use it with other equipment.
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Written by and Copyright, Phil. Storr © Last updated 6th June 2020