Assembling an HRPT System
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June 2003 Remotelmaging Group Journal lssue 73 Assembling an HRPT System Cheaplg By Gerald lhninger Some excellent articles on the subject of home-made HRPT systems have been published in the RIG journal in the last few years. In the year 2000, when I started with HRPT, my target was a very cheap system which would be useful for beginners without much electronic skill. This system should include simple kits and cheap ready-built equipment without the need for test equipment. Additionally, I wanted to have the best performance I could obtain while using only a single PC for both dish tracking and data recording. Not possible, you would think! Then let me tell you how I achieved this at a cost of only 450 euro (other than 1O0O euro for an antenna rotator). My first operational HRPT system was made using rny 7.2 m Meteosat dish but this proved too big when there was a strong wind. So I bought an 87 x 72 cm offset dish at my local electronic shop for only 25 euro and this now became my starting point. Next I considered the performance and decided that I required noise-free images down to 5'. Using rny Satlink software, I calculated that I required a low-noise-amplifier with 0.6 dB noise figure and an HRPT receiver with 3 MHz bandwidth plus a digital decoder with a 'bit integration and dump'function. A11 that remained now was to look for cheap HRPI parts to achieve this performance. HRFT System Parts For the offset dish I used a circular helical feed because of the circularly polarised satellite signal and tried some designs which I found on the Internet. I bought a stove-pipe cap to use as a reflector, 1.5 metres of 6 rnrn2 earthing wire, an N-plug as connection to the low-noise-amplifier and some screws, all for about 15 euro. I wound the earthing wire counterclockwise around a 50 mm diameter former until I had 8 turns. The helix sprang out to about 58 mm when winding was complete and I then carefully stretched it until the turns were spaced 20 mm apart. Finally, I cut off the first half turn and the last half turn to produce a7-twrn helix, drilled a hole 29 rnrn to one side of the centre of the reflector, mounted the N-plug and soldered the helix to the 46 The offsetdish The helical feed
Transcript of Assembling an HRPT System
June 2003 Remote lmaging Group Journal lssue 73
Assembling an HRPT System CheaplgBy Gerald lhninger
Some excellent articles on the subject of home-made HRPT systems havebeen published in the RIG journal in the last few years. In the year 2000,when I started with HRPT, my target was a very cheap system which wouldbe useful for beginners without much electronic skill. This system shouldinclude simple kits and cheap ready-built equipment without the need fortest equipment. Additionally, I wanted to have the best performance I couldobtain while using only a single PC for both dish tracking and data recording.
Not possible, you would think! Then let me tell you how I achieved this at acost of only 450 euro (other than 1O0O euro for an antenna rotator).
My first operational HRPT system was made usingrny 7.2 m Meteosat dish but this proved too bigwhen there was a strong wind. So I bought an87 x 72 cm offset dish at my local electronic shopfor only 25 euro and this now became my startingpoint. Next I considered the performance anddecided that I required noise-free images down to5'. Using rny Satlink software, I calculated that Irequired a low-noise-amplifier with 0.6 dB noisefigure and an HRPT receiver with 3 MHzbandwidth plus a digital decoder with a 'bit
integration and dump'function. A11 that remained now was to look for cheapHRPI parts to achieve this performance.
HRFT System Parts
For the offset dish I used a circular helical feedbecause of the circularly polarised satellite signal andtried some designs which I found on the Internet. Ibought a stove-pipe cap to use as a reflector, 1.5metres of 6 rnrn2 earthing wire, an N-plug asconnection to the low-noise-amplif ier and somescrews, all for about 15 euro. I wound the earthingwire counterclockwise around a 50 mm diameterformer until I had 8 turns. The helix sprang out toabout 58 mm when winding was complete and I thencarefully stretched it until the turns were spaced 20mm apart. Finally, I cut off the first half turn and thelast half turn to produce a7-twrn helix, drilled a hole29 rnrn to one side of the centre of the reflector,mounted the N-plug and soldered the helix to the
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The offset dish
The helical feed
lssue 73 Remote lmaging Group Journal June 2003
N-plug. A T-rod in the middle of the reflector gave the helix good stability.The offset dish was then mounted and turned by 90' with the helical feed tothe right or left side of the dish.
The next step was to find the low-noise-amplifier. Either you use the SamElsdon LNA design which is available as a kit, with the ready-built RIGdownconverter, or you can look for a much simpler design which iscompletely ready-built.
I have tried both and for the second option found asupplier in Italy called Nuoua Elettronica who offer acombination low-noise-amplifier and downconverterwith 0.6 dB noise figure and about 50 dB gain. Powersupply of 15 V comes via the co-ax from the receiver.The cost of this ready-built downconverter (TV97O) is83 euro, but you do have to protect it against rain(e.g. use a waterproof box). For best performance itshould be directly connected behind the reflector ofthe helical feed.
One of the hardest parts is obtaining a suitable HRPT receiver. Two designsare available as kits but of course these need some electronics constructionexperience as well as test equipment to adjust the receiver. There is,however, a good ready-built receiver that can be bought with your hardearned money, the LX. 1495, again from Nuoua Elettronica, for 2O7 euro.Nuoua Elettronica have their own bimonthly journal in ltaly.
After I had read the Italian article about this receiver, with some languagetroubles, I decided to buy one. Mr. Leonardo Righini, one of the companydirectors, helped me to order the receiver via credit card, and only one weeklater I had it in my possession. The first thing I did with it was to remove allPCB's and make a shielding layer inside its plastic box using a copper sprayand then connected this shield to earth.
Features of the LX.1495 Receiver
. tuneable from 135 - 155 MHz
. frequency LED display
. frequency steps: 1, 10 and 100 kHz
. 4 programmable frequency memories
. frequency and channel scan
. power supply via co-ax to the downconvertersignal meter and AFCBNC input, 2 outputs (decoder and/oroscilloscope)suitable for CHRPT
a
The TV970
The LX.1495 receiver
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IGerald subrni t ted th is l t larch 22.2043 | ' IOAA 16 image acquired wi th the HRPT systemdescr ibed in h is ar t ic le h lost of western Europe is enjoy ing c loud- f ree sk ies, whi le the snow-cappec ianges of the Fyrenees and Alps show up to advantage.
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lssue 73 Remote lmagang Group Journal June 2003
The Decoder
I decided to build the Rob Alblas digital decoder, which cost me about115 euro. This decoder is suitable for HRPT, CHRPT and HRI. Rob uses anEPROM for the decoder and he has also designed a test version with a 'bit
integration and dump' function to get less speckles in the image. Somepeople reported that although this test version produced fewer speckles itgave more bad lines (even at a high signal level) and that their images werenot useable.
But I wanted to give it a try to see this behaviour for myself. After the firstHRPT images with Rob's standard EPROM I changed to his test EPROM andwhat a miracle - it was running without any bad lines! I improved my systemperformance by up to 2 dB and feel that its performance almost matches thatof an analog decoder. But Rob Alblas, Gotz Romahn (who made somedecoder measurements) and I don't know why it is working so well with myNuoua Elettronica receiver. Then Bob Barnes used the 'bit integrator anddump' EPROM after some modifications of the Sam Elsdon receiver (see RIG721 and now it also is working without bad lines. It seems that the IF filtermodification was the reason for this success and I hope more people canverify this result.
Because of the non-inverted receiver output there was no change at thedecoder but I did have to build a simple comparator (LM311 and someresistors) with a low-pass-filter to feed the decoder input.
The -l[on Plus Utra is an antenna rotator system similar to the G5500 rotatorand costs about 950 euro. I have such a rotator and built the FodTrackrotator interface. This interface is really easy to build, cost me only 25 Euroand connects to the LPT2 port of the PC. Wrtrack is used to feed theFodTrack rotator interface with the required azimuth and elevation data.
System AdJustments
After I had built the decoder, comparator and low-pass-filter into the receiverbox and connected all the units together, I searched for the Meteosat-7 signalwith an APT receiver, adjusting the helical feed position (focal length) andazil:rutlr/elevation of the dish for the best signal. With the WxSat software Isaw a completely noise-free Meteosat-7 image.
Next I tracked a NOAA satellite and used its signal to adjust the decoder VCOtrimmer for the best signal lock. I did this with a low satellite pass (elevationabout 5" to 10"). Fina1ly, I started up my 4OO MHz PC, connected the decoderto LPT1 and the FodTrack interface to LPI2 and ran WxTrack (David Taylor),Wsat (Rob Alblas). I then recorded the first HRPT data with my new systemand got a brilliant image with the HRPT reader (David Taylor).
June 2003 Remote lmaging Group Journal lssue 73
Now I had noise-free images down to 5" with NOAA 77 and NOAA 16, about6" \Mith NOAA 12/14 and 15' with NOAA 15.
Summary
81 cm x72 cm offset dish 25 EuroHome-made hel ical feed 15 EuroReady-built LNA/downconverter - http://www.nuovaelettronica.it 83 EuroReady-bui l tHRPTreceiver-http: / /www.nuovaelettronica. i t 207EuroDecoder kit - htto://www.alblas.demon.nl/wsat 115 Euro
That totals around 450 Euro and only the helical feed, comparator anddecoder were home-made projects. If you want to use a rotator plus trackinginterface you need an extra budget of around 1OO0 Euro.
Have a look at my website
http tlm e m bers. s u rte u.aUgeral d _i h n i nge r
to see many details about my HRPT system and additional informationincluding the Nuoua Elettronica HRPT equipment.
CopA Deadline for RIG 74 is FridaA, JulA 25, 2003
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