At the time of preparing this page, most images have been obtained using my old hardware configuration: a RIG RX1 or RX2 together with the IF1 interface feeding into the bi-directional parallel interface in a 16 MHz AT286 computer. This latter is networked to other computers which are more suited for data workup, though the same software [JVFAX Ver. 7.0] is used in each.
By today's standards, this is a very old hardware package indeed, and during coming months, it's due to be superceeded by a more up to date system using faster & more modern software packages- JVComm32, SatSignal, WXSat and WxtoImg. They all have their virtues, and the jury is still out on which one I'll eventually settle upon (indeed, others may well come along to change all that.)
To begin with, I thought I'd go right back to the beginning and show one of my early images, in fact the very first one that I archived. It dates from 12th. August, 1995 and shows a morning pass, southbound, from NOAA 12. It was producing fine imagery in those days (as it still is, long past its design lifetime):
A perfectly straight picture can be obtained if the software package gets its timing data from the satellite signal itself. The later guise of JVFAX does just that by extracting a synchronising signal from the 2400 Hz subcarrier; the data is input through the parallel interface and each line is not started until the sync pulse is received from the interface. This completely gets round the Doppler shift problem, and can also be emulated in more recent packages where the decoding software derives its synchronisation from the digitised data (via the sound card) directly. Sometime one can decode synchronously or asynchronously, according to choice.
Some other problems are evident - dropouts or uneven areas of signal. These are due to deficiencies in the receiving antenna which was a 2 metre vertical intended for amateur VHF communications. In an ideal world, the receiving antenna would have an equal response in all directions from horizon to horizon. In practice, few antennas manage to come close to that, and many fall far short of the mark. A 2 metre vertical is pretty unsuitable in this case for several reasons - it's the wrong length to start with and has the wrong orientation, where horizontal would have been a bit better. The length means the impedance matching will be incorect but also that the response in different directions will vary significantly. This means that whilst a good signal will be received in some directions as the satellite passes over, in others it will fall away or even disappear - this is the cause of the dark bars at intervals. In these places the receiver AGC tries to compensate with a resulting increase in noise. There is also some computer noise from direct pick-up by the antenna as it was not far away - generally these should be as far away from each other as possible, as a precaution.
So much for that, lets look at a recent image - NOAA 17 from its morning pass on 21st. January, 2003.
The rest of this page consists of a couple of galleries which I've compiled from the archives, together with a selected picture - this is intended to be one of the more interesting pictures that I've had during the past week or so. So do come back regularly to have a look, and of course, I'd always value feedback.