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NOAA-N Prime Launched!

NOAA-N' will be the last in the series of TIROS ATN, Advance TIROS-N. NOAA-N' has a planned launch date of Friday, 6th February 2009 at 2:22 AM PST from Vandenberg Air Force Base, California, United States by a Delta II launch vehicle. Once in orbit, it will be called NOAA-19. Read more >>

All images courtesy NOAA and NASA .

APTDecoder, The NOAA POES Weather Satellite Decoder

APTDecoder is a free software for recording and decoding signals transmitted by NOAA POES APT enabled weather satellites. It is run on a NT-based version of Windows. A minimum of 128 MB of RAM is recommended. More RAM is needed if you use background images as templates. We recommend 512 MB and to be safe 1 GB of RAM and a P4 computer.

APT: Automatic Picture Transmission. A method of broadcasting cloud pictures from satellites.

APT data are transmitted continuously as an analogue signal using amplitude modulation of a 2400 Hz carrier. A new line of data is transmitted each half second containing a line of image data from two AVHRR channels together with supporting information. As each image frame is received, synchronisation patterns show up as vertical black lines to the left of each image while telemetry data are shown as grey scale wedges carrying calibration and other information. Any two of the Advanced Very High Resolution Radiometer (AVHRR) channels can be chosen by the NOAA ground station for dissemination. A visible channel is used to provide visible APT imagery during daylight, and one IR channel is used constantly (day and night). A second IR channel can be scheduled to replace the visible channel during the night-time portion of the orbit. To receive APT you need a PC, 137 MHz receiver and a dedicated right hand polarized (RHCP) antenna.

For more information see NOAA KLM USER'S GUIDE Section 4.2 (http://www2.ncdc.noaa.gov/docs/klm/html/c4/sec4-2.htm).

The general idea of this software is What You Receive Is What You Get, WYRIWYG. It does not modify your received image before you say so.

APTDecoder can create four grayscale- and colour enhanced images. Coloured images are created based on an colour lookup table (CLUT). A CLUT editor is also included. It renders the raw image (fully decoded) while recording signals transmmitted from the satellite or while processing an audio file.

It can track multiple satellites, displays satellites on a map, predict passes and footprint overlaps on a given date. Orbital elements can be downloaded and updated from a user specified url or local file.

APTDecoder has radio control support for R2FX, RIG-RX2, EMGO and ICOM PCR1000/1500/2500.

It has an advance HTML/RSS 2.0 logging system. It automatically maintains the log after the pass is recorded and uploads it to the user specified server. Logs are overwritten every day. An RSS feed reader is built-in.

An example image captured over my station and decoded with APTDecoder. This image was transmitted by the latest launched satellite, NOAA 18 (N), on 137.9125 MHz. It was launched from Vandenberg Air Force Base, Calif. at 6:22:01.566 a.m. EDT Friday, May 20 2005. Read more at NOAA N Mission home. It was recorded on Tuesday, May 31 2005 at 09:44:05-09:55:29 UTC, maximum elevation was 35° and moving north.

The image to the right is poes-weather latest received APT image at Vasa Finland.

APTDecoder is free software: It is derived from the work by Thierry Leconte, F4DWV and can be found at http://atpdec.sourceforge.net/. Mapping is done with the open source Geographic Translator (GEOTRANS) and satellite tracking and orbital prediction program PREDICT written under the Linux system by John A. Magliacane, KD2BD. Images are generated with the ImageMagick software suite.

It is delivered with source code, you can redistribute it and/or modify it under the terms of the GNU General Public License.

Receiver for the 137 MHz band

You will need a receiver that can receive from the 137 MHz band and a right-hand circulary polarized antenna.

The EMGO APT receiver by Ing. Miroslav Gola, OK2UGS. I bought one in 2004 as already assembled and tuned product. At the time it was not computer controllable and I had to use the Scan Mode to receive 24/7. I upgraded the chip in 2007 so I could control it with APTDecoder via the serial port.

This receiver is a very popular APT receiver and in my opinion one of the best.

The R2FX receiver by Holger Eckart, DF2FQ. This receiver is delivered as a plug and play product and fully computer controllable. I bought one in 2005.

If you don't yet have an APT receiver I would recommend you to purchase the R2FX. The R2FX is already boxed and has got very advance features you can control via your computer. The EMGO is not boxed, some bigger and not "that" stable for 24/7 reception. But all in all, it does a good job. I have also tried the ICOM-PCR1000 and it works but you will not get as good images as with the above ones.

If poes-weather would choose the APT receiver for you it would be, of cource, the R2FX receiver. This is the ultimate APT receiver.

Antenna for the 137 MHz band

The most important is the antenna. A popular cheap antenna is the Turnstile. A homebrew helix is what most of APT stations use but if you are not the Do It Yourself (DIY) one, it will be the most expensive part after the PC and will most likely not perform as good as you expected.

If you are the DIY one, then let me introduce you the Double Cross Antenna (DCA) developed by Jerry Martes using The Cross Concept ©. The Cross Concept is two crossed dipoles fed in phase spaced 1/4 wave length apart, The Simple Cross Antenna. The DC is two simple cross antennas connected togeather. The other pair is fed 1/4 wave later. This antenna is very sensitive toward the horizon and is the ultimate APT antenna when receiving low elevation satellite passes. The image to your right is a NOAA 18 1.7 max elevation pass received using a Double Cross antenna made of 8 mm aluminium pipes. The antenna weight is less than 500 grams and cost less than 15 eur ($20).

Jerry Martes Double Cross Antenna article in the QST magazine February 2008 and Jerry & Patrik GEO article in December.

Double Cross Antenna - A NOAA Satellite Downlink Antenna by Gerald Martes, KD6JDJ

Signal Plotter and Double Cross Antenna by Jerry Martes & Patrik Tast

Double Cross Antenna Kit for the 137 MHz band

Read also document Double Cross Antenna For Beginner (2.8 MB DOC). Browse through more DCA construction images and documents in folder jerry at the User Files section.

If you are using a Quad Helix Antenna read this document QHA (26 kB Doc)

The image below to the left is the ideal Right Hand Circulary Polarized Elevation Plot of the Double Cross antenna generated with the EZNEC antenna software. To the left is the real anenna plot of NOAA 12 recorded portable with APTDecoder software and R2FX receiver.

NOAA 12 maximum elevation 84° on Sunday, 22 July 2007.

Double Cross Antenna (DCA) build instructions

Fred E. Piering has documented his DCA build carefully with a general partlist (available from US Lowres, Home Depot), assembly hints and SWR measurements of the antenna.

DCA Assembly Hints.pdf

For my latest DC I used 8 mm aluminium tubes as dipoles and spaced each dipole 500 mm. I used 20 mm electrical PVC tubes for the "arms" and 3 mm plexi-glass as the center to fasten the arms. The dipoles are from tip to tip 1000 mm. I cut the tubes to 500 mm (eight pieces) and join them with some non electrical conductors, I used PVC.

Phasing harness: Let us call one pair of the simple crosses for the Nort/South (N/S) and the second East/West (E/W). I cut 360 mm of RG58U for the N/S dipoles and 720 mm for the E/W dipoles, 1/4 wave longer in coax. I connected them as shown in the sketch and tilted each dipole to the right (as seen from the top) about 30 degrees so it will form a box.

I bet you will have a lot of fun with The Double Cross APT Antenna and The Cross Concept).