My APT Receiving Station

Having an interest in Space, Meteorology, Amateur Radio, Electronics & Computers this appeared the ideal hobby/project to bring all these tasks together with one common aim of receiving images directly from space satellites in real time.

After reading articles in Short Wave Magazine, which initially fuelled my interest, I joined RIG (Remote Imaging Group) whereby I gained further interest and knowledge then purchased the kit of components to build the excellent RX2 Wxsat. 

RX2 Receiver

This took around a week to build, spending an hour or so each evening. The trickiest part was ensuring the correct capacitors were fitted correctly and making a suitable case, which looked both pleasant and functional, hopefully not looking to amateurish. The setting up and testing was fairly straight forward with the use of a digital multi-meter, plus tuning in the receiver to the now familiar ‘Tick-Tock’ sound of an overhead satellite. The initial times of the overhead satellite passes were taken from the satellite prediction chart published in RIG. At this point the antenna was a rubber duck taken from a handheld scanner.

The Antenna

The signals from the NOAA APT weather satellites are transmitted with right-hand circular polarisation. Therefore I needed to have a proper antenna so I purchased a crossed dipole (or turnstile antenna), designed and tuned specifically for the 137 MHz band. This was positioned at about a height of around 4 metres attached to the rear of my garage. The coaxial cable was RG58 terminating onto a BNC connector.

The PC Decoding Software

The PC is an old Pentium 2, but perfectly suitable for remote imaging. My choice of software at the time was Wxsat, it is probably the simplest entry-level soundcard program. Wxsat can decode images in real-time. The program can simultaneously save the image as a bitmap and store the raw data as a WAV file for future decoding and manipulation as the signal is being received.

PC Tracking Software

If you wish to know exactly when your chosen APT satellite is going to appear above your horizon, you require the assistance of a satellite tracking program. My choice was to use and still is the excellent Footprint software. Footprint is a freeware program that is easy to approach for a beginner and provides all the basic facilities needed for predicting satellite passes over your location. 

The initial Results

Right from the outset the first results were encouraging, as is always when venturing into something new, one wants to achieve results just like those coloured images in magazines. Due to the antenna not being very high the overall pass barely covered the UK, even though the quality of the image was acceptable.

A couple of years on 

I am now a member of GEO (Group for Earth Observation) and I continue to still use the same RX2 receiver, however this is now connected to a home-made Quadrifilar Helix (QFH) antenna, the antenna is made using coax radials fitted around a support of wooden doweling and plastic piping. The design was based on an article by radio amateur W3KH, and modified slightly to meet my own construction ideas. To further increase the signal gain I have also attached a masthead pre-amp available from GEO. The height of the antenna now reaches around 30ft by the use of a telescopic aluminium mast, attached to the rear of the garage.

The software used to capture the initial data/images is still Wxsat, however I further process the images with the superb Wxtoimg software or SatSignal.

I continue to use Footprint satellite tracking software even though its fairly basic it does more than what one requires. I have also used Wxtrack, but always return to Footprint.

The results now are just like those in other magazines, the span of image is from North Africa to the Arctic Circle with no drop-out’s. Further examples of my images are on the following page APT Images. Much to my delight some of my images have also been published in RIG and GEO over the past years.