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HF Weather Fax FAQ

HF Weather Fax

To use this app, you need to feed the audio output from a your radio into the device. You can do this via one of several ways:

  • Set the device near the radio's speaker to pick up the audio. While easy to do, this is not ideal, as background noise can interfere with the audio, causing garbled decodes.
  • Plug headphones into the radio, and set one earphone near the mic. I find that with good quality headphones, this can work extremely well.
  • Use the microphone input jack of your device, by obtaining an appopriate cable and connecting the radio's line level output to the microphone input.
  • With the Camera Connection Kit, you can plug a USB sound input device into the iPad, and use a patch cable between it and the radio's audio output. This is by far the best solution.
You can use the volume indicator in the upper right corner to verify that audio is getting into your device, and that the volume level is appropriate.

If you are running iOS 7 or later, be sure to give the app permission to use the microphone. If you denied permission, you can always give it again by following these steps:

  • Open Settings app and go to "Privacy"
  • Select "Microphone" to get a list of all apps that have requested access to the microphone, and to control which apps have access to the microphone

If you're looking for a radio to use with the app, there are many different types to choose from. Take a look at our listing of radios to use with your app, to see several, along with some suggestions on how to choose a radio.

Tune your radio in USB mode to the weather fax frequency, making note of the fact that you usually need to tune about 1.9 kHz lower in frequency than the listed carrier frequency in a schedule. Fine tune your radio for proper reception of black and white picture elements.

When first using the app, it is normal for the received image to be slightly slanted, due to slight timing variations between devices. This can be corrected by the timing adjustment value, which is located at the top of the screen between the - and + buttons.

The default value is zero. If the received image is slanting to the right, the timing adjustment must be increased. Press the + button a few times.

If the received image is slanting to the left, the timing adjustment must be decreased. Press the - button a few times.

Now wait several seconds, and see if new picture information for the fax is no longer slanted. (previously received picture information will not be changed) Continue to make adjustments as necessary.

The timing adjustment value will be automatically saved and used each time you run the app, so typically you only need to go through this procedure once.

Tapping on the Stop button will stop reception, the button title will then change to Start, tapping it again will start reception.

Tapping the next button to the right will toggle Auto save mode on and off. When set to Auto, the stop tone of a fax will be used to save the received image. You can also tap on the Save button to manually save an image. You can access saved images on your computer via iTunes:

  • Go to iTunes, and select your device from the DEVICES list at the left
  • Tap the Apps tab
  • Under File Sharing, select HF FAX from the list of Apps
  • All of the image files will be under HF FAX Documents. You can transfer these files to your computer.

Tapping on the View Saved button will bring up a list of the saved images. Tap the name of the image of interest, and it will be displayed. You can then delete the image, if you wish.

Tapping on the Schedules button will bring up a copy of the NWS/NOAA weather fax schedule. You can tap on Download Latest to get a copy of the current schedule. You can also tap on Default Schedule to erase any downloaded copy, and revert back to the default copy that comes with the app.

Note that proper reception of fax images and detection of the start and stop tones requires good quality reception. Weak signals, noise and other interference can make it difficult or impossible to properly decode and display a fax image.

The start tones sent at the very beginning of a fax image transmission are also used to align the left and right sides of the fax image. If they are not properly received, the image will not be centered. Typically you will see a black bar running down the middle of the screen somewhere when this happens. This will also happen if you tune in a fax transmission after it has started, since the start tones will not have been decoded.

The solution is to get a better quality received signal on your radio, as well as make sure the audio from the radio is getting into your iPad/iPhone without distortion. Often plugging headphones/earphones into the radio, and placing them next to the microphone of your iPhone/iPad will help.

Here are some details on directly connecting an audio line source to your iPad/iPhone/iPod Touch

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Last modified November 25, 2014