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Orbital Weather Satellite APT Image Reception

Posted: Mon Oct 09, 2017 7:49 am
by RSP2user
Key Words: Weather Satellite, NOAA, WEFAX
Weather Satellite Reception 1 of 3
This is a 3 part post due to the limitations for loading images into this bulletin board.

APT weather satellite image reception is very straight forward and easy to do from almost anywhere on Earth. Currently, as of 2017, there are still a handful of orbital weather satellites transmitting the APT or Automatic Picture Transmission format. As a minimum, you will need an antenna, a radio receiver capable of receiving FM frequencies from 137.1 to 137.9125 MHz having a bandwidth of 30kHz to 50kHz, such as the RSP2, a personal computer with a reasonably fast microprocessor, and image decoding software. To gain a much better range for receiving images, an 18dB low noise preamplifier is required. Without the 18dB preamplifier, you can get good APT reception for about 40 to 60 degrees of an overhead satellite pass when applying the antenna below and the RSP2. With the preamplifier, you can potentially receive images within a few degrees of horizon-to-horizon. With the configuration described below using a backfire quadrifilar helix antenna and applying an 18dB 0.6dB noise figure or better low noise preamplifier mounted at the antenna, you can use the RSP2 to obtain some very nice APT weather satellite images, such as those shown in the following examples:

NOAA 19 64E Chan A.jpg
NOAA 19 64E Chan A.jpg (153.32 KiB) Viewed 12499 times
NOAA 19 59W.jpg
NOAA 19 59W.jpg (157.98 KiB) Viewed 12499 times


A very effective antenna for receiving the right hand circular polarized APT signal from orbital weather satellites is the backfire quadrifilar helix.

QFH Antenna.JPG
QFH Antenna.JPG (38.77 KiB) Viewed 12499 times

What you will need:

1) 25ft (7.62 m) of 6 awg bare copper wire. This can usually be found at a reasonable cost in the electrical wiring section of many hardware stores. It is important that it is coiled, but not tightly, in its packaging and that it is without kinks that cannot be easily straightened. If it comes in a coiled form, this is helpful in forming the antenna elements.
2) Long clear acrylic tube 1 inch (2.54 cm) diameter by 1 m or approximately 3 ft long (the length does not have to be exact as long as it at least 30 inches (76.2 cm). The diameter is critical as the antenna center tube will additionally be used to form the balun. The wall thickness of the tube should be 0.125 inches (0.3175 cm).
3) Short clear acrylic tube 0.625 inch (1.5875 cm) diameter having a length of at least three inches. This smaller tube will be cut to form an internal washer/support in the larger tube. Alternatively a thick plastic washer of some type can be applied as long as it fits snugly inside the larger tube described in 2) above and is around 0.25 inch (0.635 cm) thick. Ensure that the washer is not metallic or made of any substance that can interfere with RF.
4) 5 ft (1.524 m) of 18 awg enamel coated magnet wire.
5) 3.5 ft (1.0668 m) of RG-8x or RG 58U coaxial cable.
6) Chair leg end cap to fit a 1 inch or 2.54 cm diameter tube. These are typically available from hardware stores.
7) Soldering iron or propane torch and solder capable of soldering 6 awg copper wire.
8) Heavy duty industrial glue, such as 3M Scotch-Weld™ DP-420.
9) Two part 5-minute epoxy.
10) Permanent marker.
11) Measuring tape.
12) Pliers for bending the 6 awg copper wire into the required element form.
13) Saw for cutting the acrylic tubing.
14) Good quality, non-metallic, outdoor enamel paint.

Continued in Weather Satellite Reception 2 of 3.

Orbital Weather Satellite APT Image Reception

Posted: Mon Oct 09, 2017 7:58 am
by RSP2user
Key Words: Weather Satellite, NOAA, WEFAX
Weather Satellite Reception 2 of 3
This is a 3 part post due to the limitations for loading images into this bulletin board.

Continued from post 1 of 3.


Read the following information carefully and be clear on the construction, before starting. First review the antenna images and figures below to get a good idea of how to form the antenna. Your exact construction of the antenna will depend on tools and materials that you have available. The antenna elements are made from the continuous piece of 6 awg copper wire by bending it at the required bend points to form the elements. You will need to use a permanent marker to first mark where the bends in the wire will be. Do not start bending the 6 awg wire yet, just mark it. You will need to cut notches in the top of the long acrylic tube and drill all of the holes needed to form the antenna and balun. Review the corresponding sections below. You will then need to cut two 0.25 inch (0.625 cm) lengths of the 0.625 inch (1.5875 cm) diameter tube to form thick acrylic washers. These thick acrylic washers will be used to support the 6 awg copper wire at the top of the tube.

QFH Dimensions.png
QFH Dimensions.png (60.52 KiB) Viewed 12500 times

Fig. 1 Dimensions:

Large Loop (Black)
D1 = 15.11 inches (38.38 cm)
H1 = 21.92 inches (55.67 cm)
Length of Vertically Wound Section of Half Large Loop = 32.31 inches (82.07 cm)
Perimeter of Entire Large Loop = 94.85 inches (240.92 cm)

Small Loop (Blue)
D2 = 14.16 inches (35.86 cm)
H2 = 20.53 inches (52.14 cm)
Length of Vertically Wound Section of Half Small Loop = 30.26 inches (76.87 cm)
Perimeter of Entire Small Loop = 88.84 inches (225.67 cm)

QFH Antenna Side View.JPG
QFH Antenna Side View.JPG (46.36 KiB) Viewed 12500 times

QFH Loop Connection Top.JPG
QFH Loop Connection Top.JPG (55.48 KiB) Viewed 12500 times

Drill the required holes and cut 4 notches into the long acrylic tube as shown (it helps to drill 4 holes; one at the bottom of each notch and then use a coping saw to cut down to each side of each hole). Make the holes for the 6 awg wire in the acrylic long tube just large enough to snugly fit the 6 awg wire through. With industrial glue, glue one acrylic washer inside the long tube so that its top edge is in line with the bottom of the 4 notches. The 6 awg copper wire will rest on this and be glued in place to it later. Let the glue for the washer dry overnight. Next form the balun using the 18 awg magnet wire. Drill 1/16 inch diameter holes to feed the 18 awg magnet wire through. The balun will be located at the top of the tube, just under the acrylic washer. Make the top two wires of the balun long enough to extend out of the top of the tube where they can be attached to the 6 awg wire later without melting the acrylic tube. At the bottom of the balun, you will need to drill a larger hole on each side so that you can temporarily pull the bottom wires of the balun through and the wires from the coaxial cable through and solder them. Once these are soldered, you will cover them with heat shrink tubing and carefully push them back to the inside of the acrylic tube. Fill these holes with 5-minute epoxy, once the soldering is completed. Glue the balun in place with 5-minute epoxy as a coating.

Next, form the elements. This will be done with the continuous piece of bare 6 awg copper wire. Mark the spots where the wire will be bent to form the elements. Do not start bending the wire yet. Just mark the wire. Next, carefully feed the wire through the bottom holes for the short loop in the acrylic form and straighten the 6 awg wire to form the bottom straight section of the small loop. Then start forming the first and second bends in the 6 awg wire starting from the center of the bottom of the small loop outwards. The concept is to form the elements as you go, not all at once. When forming the rounded portions, note the direction of the coiled wire that you are forming and use that to your advantage when making the sharp bends to form the elements. The sharp bends should have a radius of curvature of 0.2 inches (5 mm). If done correctly, the rounded coiled portions will nicely form the rounded portions of the helical-shaped elements. Be very careful not to put stress on the acrylic form, particularly at the notches, and do not use the acrylic form to try and bend the 6 awg copper wire as the acrylic form will break. Carefully form the remainder of the long and short loops, noting the 90 degree bend at the top. Also, to keep the bottom of the long and short loops in place, you can apply a small amount of 5-minute epoxy to hold them in place while working to form the loop elements. The ends should meet at the top at a 90 degree angle. Ensure that the length of each element is correct. Pull the copper ends to be soldered up above the acrylic tube form temporarily and carefully. Use a large soldering iron or propane torch to solder the two ends together at a 90 degree angle. Be very careful doing this. Pull the two balun wires at the top up through the acrylic form, temporarily lift the two 90 degree element corners up from the notched end and solder one of the top wires of the balun to each corner. Be sure to use a piece of sand paper to remove the enamel coating from the balun wire ends, before soldering. Make sure you get these balun wires soldered to the 6 awg wire correctly, before applying a lot of glue at the top to hold everything in place. Next, place the 6 awg wire down into the notched end of the acrylic tube and carefully tuck the balun wire back in. Use a small amount of 5-minute epoxy to glue to hold the 6 awg copper wire at the top of the acrylic form in place. Once that dries, apply an additional amount of industrial glue to the 6 awg wire at the top of the form and insert the second acrylic washer. Ensure that there is a sufficient amount of glue to strongly hold the top wires in place, once dry. After the industrial glue dries overnight, take the plastic chair leg cap, cut the length to suit you, and then apply a small amount of 5-minute epoxy onto the tube at the top and push the plastic chair leg end cap down onto the top of the acrylic tube, gluing it in place and forming a watertight seal. Be sure to fill any remaining holes or gaps, except for the bottom of the acrylic tube form, with a small amount of 5-minute epoxy to ensure a watertight seal.

The RG-8x or RG-58u coaxial cable should already be fed down the inside length of the acrylic tube. If you have not already done so, attach a connector to it. You can now connect up the backfire quadrifilar helix antenna for testing. If you do not yet have an 18 dB preamplifier, you can attach the antenna with appropriate connectors, directly to the RSP2 and still obtain a good APT image for approximately a 40 to 60 degree arc on a direct overhead pass of an orbital weather satellite. You can verify operation with SDRplay’s SDRuno software to check the signal level and/or apply the application software described below to check actual satellite imagery.

Once the antenna has been fully tested, paint it with a non-RF impacting, non-metallic outdoor enamel spray paint to weatherize it. When mounting the antenna permanently, ensure that you have a proper lightning protective ground line attached to the conductive shielding of the coaxial cable running back to the RSP2. Additionally, to obtain the best results, ensure that the antenna is mounted high enough to obtain a reasonable line of site to the horizon in each direction. With a slight widening of the end of the metal mounting mast tube, a standard antenna mast tube can be used and a few inches (5 cm to 7.5 cm) of the bottom of the long acrylic tube can be mounted inside of it with a single bolt holding it in place.

Continued in post 3 of 3.

Orbital Weather Satellite APT Image Reception

Posted: Mon Oct 09, 2017 8:04 am
by RSP2user
Key Words: Weather Satellite, NOAA, WEFAX
Weather Satellite Reception 3 of 3
This is a 3 part post due to the limitations for loading images into this bulletin board.

Continued from post 2 of 3.


The balun is formed using 18 awg enamel coated copper magnet wire wrapped around the long acrylic 1 inch (2.54 cm) diameter tube, just under where the top of the copper elements are seated. Drill three pairs of vertically spaced holes placed 0.297 inch (7.5 mm) apart at 90 degree intervals around the tube. Each of the three inductor coils are to be wrapped counter-clockwise two turns when looking down from the top of the tube. With the two holes for the center coil facing you, start wrapping the first coil for the balun from the top left hole and evenly space the windings, ending in the bottom left hole. Next wrap the center coil, winding it from the top center hole going between the windings of the first coil so that no overlap occurs and ending in the bottom center hole. Now wrap the third and final coil starting at top right hole and wrapping it between the existing coil windings so that no overlap occurs and finish in the bottom right hole. Connect the top of the center coil to the bottom of the left coil (first coil). Connect the bottom of the center coil to the top of the right coil (third coil).

Balun Diagram.JPG
Balun Diagram.JPG (17.36 KiB) Viewed 12479 times

Balun.jpg (31.23 KiB) Viewed 12479 times


The preamplifier applied in this example has 18 dB of gain with a 0.6 dB noise figure and runs off of the 5VDC Bias-T power feed through the coaxial cable from the RSP2. There are manufacturers of 18 dB preamplifiers on the Internet; however, you will need to either interface one of these with a separate power supply, or ensure that it will operate properly with the RSP2 Bias-T and assemble an appropriate power interface for it in order to draw power through the coaxial line. Check with the SDRplay team for the voltage and current drive specifications of the Bias-T connection on port B of the RSP2.


You will need software to decode the audio signal received from the orbiting satellite. WXtoIMG software is available for decoding images. With the RSP2, and a professional version of WXtoIMG, you can apply virtual serial port emulator (VSPE) software to set and control the frequency of the RSP2 automatically as each APT satellite passes. You will need audio loop back software to take the audio from the output of the RSP2 and loop it back to WXtoIMG without loss of audio signal integrity. LoopBeAudio was found to work well for this application. Without an audio loop back software package, such as LoopBeAudio, the SDRuno audio output will not be fed into the WXtoIMG audio input. When operating LoopBeAudio with SDRuno and WXtoIMG, good results can be obtained by setting the combination of SDRuno audio level and personal computer audio level to read a volume level of around 57 to 60 on WXtoIMG when you have a strong satellite signal and the satellite is passing close to overhead. The Orbitron software will allow you to determine when orbital weather satellites are going to pass over your location. With the Orbitron software, you can monitor multiple satellites at one time.

WXtoIMG: Archived at: ... downloads/ Key information and guide:

In your first few attempts at capturing APT images, do this manually so that you can get a feel for how WXtoIMG works. When you are ready to automate the frequency control, then go to the Options>Recording Options setting of WXtoIMG and set the receiver type to Kenwood. The RSP2 emulates the Kenwood commend set. Set up VSPE for a single serial port (Device Type: Connector) and map both WXtoIMG and SDRuno to that port, Note that the serial port must be in the range of 1 to 8 and not otherwise used by the personal computer or its peripherals in order to operate. Once the serial port has been set up through VSPE and is active, then start SDRuno and from the RX Console select SETT>CAT and set the COM Device. Set RX MODE CTRL. Set the baud rate on both WXtoIMG and the SDRuno CAT tab to 57600. Select ENABLE & CONNECT on the SDRuno CAT tab. On the next recording pass of an active satellite under WXtoIMG, the WXtoIMG software will now control the frequency setting of SDRuno. You can now set up to completely automate the capturing of orbital weather satellite images. If you do not have the professional version of WXtoIMG, you will not be able to set the receiver type to Kenwood and automate the image reception using WXtoIMG.

For optimized operation using SDRuno, set the Sample Rate to 2.0 MHz, DEC 1. Set the IF Mode to Zero-IF, Set Input Level Display to Gain. When applying an 18 dB preamplifier, set the RF gain to 84.5 and set the IF gain to 40dB (IF AGC is off). Ensure that the bandwidth is set to WFM 60 kHz and then under AUX SP, reduce the bandwidth slightly to 50 kHz. Make sure NR is not selected and that NBOFF is selected. Set AGC on the RX Control panel to SLOW. Refer to the image below. To obtain a clean view of the signal waveform in the Main SP window, select Main SP>SETT>FFT and set the value to 32.

WXtoIMG and RSP2 with SDRuno.JPG
WXtoIMG and RSP2 with SDRuno.JPG (219.64 KiB) Viewed 12479 times

End of 3 part post.

Re: Orbital Weather Satellite APT Image Reception

Posted: Sun Nov 05, 2017 9:49 pm
by RSP2user
Below are additional images made using the setup described.

3 satellite pass composite image. In many instances, just two passes will cover the United States; however, a third pass was collected in order to obtain a better view of the hurricane just off the East coast.
NOAA 18 and 19  IR Compilation.jpg
NOAA 18 and 19 IR Compilation.jpg (211.12 KiB) Viewed 12105 times

Near-overhead pass with maximum reception duration (note that the image stretches from just below the arctic circle to just above the equator).
NOAA 19 86E IR.jpg
NOAA 19 86E IR.jpg (245.23 KiB) Viewed 12105 times

Re: Orbital Weather Satellite APT Image Reception

Posted: Sat Nov 11, 2017 9:18 pm
by RSP2user
NOAA_19_63E.jpg (161.55 KiB) Viewed 11692 times

Re: Orbital Weather Satellite APT Image Reception

Posted: Sun Nov 19, 2017 6:15 pm
by RSP2user
Related articles:

HRIT and LRIT Geostationary Weather Satellite Image Reception

HRIT and LRIT Low-Cost System

Orbital Satellite HRPT Image Reception

Re: Orbital Weather Satellite APT Image Reception

Posted: Sat Jan 27, 2018 8:07 pm
by RSP2user
NOAA 19 201801052139 HVCT APT with Precip.jpg
NOAA 19 201801052139 HVCT APT with Precip.jpg (182.15 KiB) Viewed 10067 times

Re: Orbital Weather Satellite APT Image Reception

Posted: Sat May 26, 2018 9:14 pm
by RSP2user
Here are some updated APT images, The increased maximum range was due to monitoring and adjusting gain in SDRuno at the beginning and end of the pass.

201804272152 APT BW NOAA 19 LR.jpg
201804272152 APT BW NOAA 19 LR.jpg (218.86 KiB) Viewed 7214 times

Here is another recent APT image:

201802102125 MSA 62E 2 N19 LR.jpg
201802102125 MSA 62E 2 N19 LR.jpg (210.68 KiB) Viewed 7214 times

Here is SDRuno in operation with WXtoImg:

NOAA19 pass SDRuno RSP2 LR.jpg
NOAA19 pass SDRuno RSP2 LR.jpg (218.88 KiB) Viewed 7210 times

Re: Orbital Weather Satellite APT Image Reception

Posted: Fri Dec 28, 2018 5:03 pm
by RSP2user
There is now a "WXtoIMG Restored" web site having the software and license information for WXtoIMG:

As an alternative to building a QFH antenna, there is a well-designed QFH antenna on the web store for Diamond Antenna. Refer to the Diamond DP-KE137.

The author of this post is not affiliated with the original WXtoIMG web site or the WXtoIMG Restored web site or Diamond Antenna or