Recorded at Northampton UK by G6KIZ
Currently there are 3 fully operational NOAA APT weather satellites in operation NOAA 15 NOAA 18 and the latest NOAA 19 which was launched on the 6th February 2009.
NOAA 17 developed a serious fault in February 2010. The fault resulted in badly degraded images which then impacted composites built using them. For this reason I took the decision to cease recording of NOAA 17 images entirely however release 2.10.7 of WXtoImg provided the option of excluding specific satellites from composite images so this option was used instead. From May 8 2010 most NOAA 17 passes produced good images with only the occasional poor one but I don’t recall seeing a good one lately so I am using the WXtoImg 2.10.11 option to exclude in from the web pages. The NOAA POES status page should carry the latest information.
All the satellites are in approximately circular polar orbits at around 850km altitude and transmit 10w RF in the 137-138MHz band which makes them relatively easy to receive with a simple antenna. The main problem with reception in the UK is the staggeringly stupid decision to allow text pagers to operate in the same band. The authorities would doubtless argue that any problems are the fault of the APT receiver but low cost equipment cannot realistically be expected to cope with the intermodulation interference caused but a powerful nearby transmitter operating a few KHz away from the satellite frequency. The result is that pager interference will be seen on most of the pictures here as short dark lines where a pager signal wiped out the satellite. The demodulated signal is processed through a normal PC soundcard and the two greyscale images at different infrared wavelengths combined to produced the false colour images displayed below.
The MCIR-precip composite images give a good idea of where there is likely to be rain by use of bright false colouring. Looking at two images recorded a few hours apart can usually show the probable path the rain will follow. Note though that the colours are only an indication of possible rain not that rain is actually reaching the ground.
Pager tower causing the interference bars
This tower is less than a mile away and operates just 60Khz above the nearest satellite frequency – avoiding the interference is
impossible difficult. I changed the impossible to difficult following some feedback from Michael Gill G6HOM who tells me that he constructed a stripline filter which successfully removed pager interference back in the ’80s or ’90s. I think I’ll have to see if there is anything amongst the junk stalls at the next amateur rally I attend which would allow me to give this a try without breaking the bank.
View Larger Map
I noticed that sometimes my map overlay was becoming seriously wrong. Investigating the problem I realised that a clock error of just a second or two could account for it. By default my Windows 7 resets the PC clock to an internet time server every 7 days. I now have amended my registry using regedit to set the clock more frequently and will watch to see how things go. The registry key involved is…
Right click on ‘SpecialPollInterval’ in the right hand column and select Modify>Decimal. The decimal number is in seconds. I have set mine to 10800 (3 hours) which is probably a massive overkill but costs me nothing.
I noticed another overlay error today. On checking I found updating the time using the default time.windows.com had a timeout. I overtyped the timeserver to use europe.pool.ntp.org instead which will hopefully be more reliable. This PC isn’t all that old but I’m wondering if it needs a new CMOS battery already and will change it if I remember next time I take the lid off the case.
Paul Glover has pointed me to Dimension 4 which he has started using successfully and seems to do pretty much what I have done with the above. I’ll leave mine as-is until such time as I see another problem and then will probably give this a go.
Paul Glover’s images
These images donated by Paul Glover of Worthing illustrate just what can be achieved with fairly modest amateur equipment when there is no local pager tower intermodulation interference.
Feel free to download any images for your own purposes – they can make attractive desktop wallpapers for instance.
During the second half of April 2013 I have not had any decent passes of NOAA 18. I’m not sure quite why and as I’ve been away from home most of the time haven’t been able to investigate properly. I’m hoping it will be possible for me to fix this as following the demise of NOAA 17 there are only 3 APT satellites left and I don’t think there are plans for further launches. Now NOAA 18 passes are poor quality. It looks like the radio is either off tune or failing to change channel. Another possibility is that the antenna was damaged in the recent very high winds.
Well having taken a look it seems that the R2ZX radio was playing up. I power cycled it and it seems to change channel OK now. I have had a similar problem before and put the radio on a time switch to turn it off and on once a day. It was still on that timeswitch but the buttons on it must have been touched as it was no longer on the auto setting so hadn’t been power cycling.
Weather satellite images recorded at Northampton, United Kingdom
Latitude: 52.226, Longitude: -0.905 Software: WXtoImg version 2.11.2 beta Receiver: R2ZX Antenna: Bill Sykes and Bob Cobey QFH
Next Scheduled Satellite Pass - NOAA 18
Start of Pass : 29 Aug 16:31 GMT Daylight Time
Time Available : 29 Aug 16:44 GMT Daylight Time
Click on any thumbnail image below to see it at full size
Next Scheduled Satellite Passes over Northampton, United Kingdom
* local time is GMT Daylight Time.
What was the best thing before sliced bread?
Since converting DigitalHam to use WordPress I have added some old email conversations as comments.