NOAA APT weather satellite images
Recorded at Northampton UK by G6KIZ
R2ZX receiver
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.
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Map overlay
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…
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\TimeProviders\NtpClient (SpecialPollInterval)
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 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’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.
Problems
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 15 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 2.10.11 Receiver: R2ZX Antenna: Bill Sykes and Bob Cobey QFH
Next Scheduled Satellite Pass - NOAA 15
Start of Pass : 21 May 07:26 GMT Daylight Time
Time Available : 21 May 07:38 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. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Is it true that cannibals don’t eat clowns because they taste funny?
Since converting DigitalHam to use WordPress I have added some old email conversations as comments.
Hi
I too am having problems with pager breakthrough on 18 mostly. I have looked and found a very strong pager data transmission on 137.975 MHz NFM. This i belive is coming from the nearby BT tower at Ozleworth in Gloucestershire, around 5 miles from myself. I wondered if you have found any solutions to the problem.
I am using a timestep Proscan 4.1 along with a home brew QHF antenna, the program is WXtoimg.
I was looking at the small Helical Resonator Notch Filter, but fear that the closeness of the transmitter and the subsequent losses through the filter would just reduce the receive signal of the satellite and not clear the full interference.
I would be interested in your findings, and share if possible how to reduce the problem.
Regards
Phil Daniels G1USW
Phil,
As near as I can tell my local pager tower transmits on 137.970MHz but it could well be 137.975MHz.
Someone contacted me and said they’d had some success using a stripline filter but they are difficult to construct and like you I’m not 100% convinced of success.
One idea I’ve toyed with trying in my own case is using a simple horizontal dipole. The tower I have problems with is more or less due east so a horizontal dipole arranged with the tower in its null would have maximum pickup on a north south axis which is of course the path that the NOAA satellites take. Horizontal only would lose 3dB against circular but the satellite signal strength is high enough for that to not really matter. I could also afford to lower the dipole below rooftop height and gain some additional screening that way. The question is how deep would the dipole null and cross polarisation with the pager transmissions (which I’m assuming are vertically polarised) be and could I produce a good enough balun so that pickup on the coax didn’t just nullify any advantage. I did a very rough and ready check using a dipole on a handheld scanner and it wasn’t very encouraging but will probably try again later.
Mark G6KIZ
I somehow lost a weeks worth of images. Not sure what caused it but all I did to get it going again was shut down WXtoImg and restart it.
Thanks to Paul Glover for drawing my attention to the problem.
Another days worth of images lost fixed by restarting WXtoImg. I’ll need to try to find the time to monitor this process more carefully. It’s all very strange as it has run trouble free for several years until just recently. :(
I’m still having problems with WXtoImg stopping processing passes. I suspect it is caused by losing my internet connection which of course happens if I reboot the router for any reason or there is an actual service interruption. I’ll make an effort to restart WXtoImg whenever I do this myself or my ThinkBroadBand monitor shows there has been an outage. Unfortunately I’m bound to miss some still so I guess I’ll just need to monitor the process more carefully.