In this tutorial we are going learn how to send pictures over the radio using the DM-1801 radio and a mobile phone




Understanding Slow Scan Television

Unlike regular television where the picture updates every ~0.04 seconds, slow scan television (SSTV) will send a picture over several seconds. A common SSTV mode Robot36 takes 36 seconds to send a picture. Longer times usually result in a higher quality image. While a TV signal is 1.3MHz, an SSTV signal is typically less than 3KHz (0.003 MHz) which is why we have to send the image slower. The advantage of using a smaller bandwidth is that we can use conventional handheld radios to send pictures.

There are many SSTV implementations, called modes. The common ones are Scottie, Martin, Robot, and PD. The different modes are just different ways of converting the picture into a signal.

This activity works best when someone else is available to receive your transmissions.

Configuring your radio

  1. The first thing we are going to do is configure the radio for a simplex frequency. That is we are not going to use a repeater.
  2. Switch the radio to VFO mode by using the VFO/MR button (highlighted). The radio should be displaying two frequencies like pictured.

  3. Switch the radio to FM mode by pressing the "A/B" button (highlighted). The radio should now be displaying "FM" in the top left corner.

    Analog FM repeaters are much easier to configure and use than DMR (digital mobile radio) so we will be using analog FM in this example.

  4. Now we need to set the frequency of our radio.

    First make sure that receive frequency is selected. This is indicated by a < symbol next to either smaller RA or RB

    To switch between receive (RA) and transmit (TA) use the function key + up (for receive) or down (for transmit).

    The A or B refers to a memory bank, allowing you quickly switch between two configurations. It's fine to use either - if you wish to switch between them you can use the function button + A/B button to change

  5. With receive frequency selected, type in the frequency you wish to use. In Australia 433.775 is the 70cm SSTV calling frequency

    Downlink: 433.775
    Uplink: 433.775

    Type the frequency in with the number pad. The decimal point will be filled in automatically for you. You can either pad the number with 0's or hit menu key confirm if the number isn't long enough to fit.

    The transmit frequency will also adjust. We'll fix that up in the next step

  6. Now select the transmit frequency to adjust by pressing the function button + down

  7. Just like setting the receive frequency, set the transmit frequency. This will be the same as your receiving frequency : 433.7750MHz

  8. By default the radio is configured to transmit with 1 watts of power. Use the function + right arrow to adjust the power up to maximum - 5W. This will give us the best chance at a successful contact

Adjusting the levels

  1. Next up we need to connect your phone to your radio and adjust the audio levels. These don't need to be perfect as SSTV is very forgiving but we need to get them close enough.

    Connect the "APRS" cable to your phone and the other end to your radio. Phones actually follow two different standards for the headphone jack so a provided adapter is included. If the instructions don't work try adding or removing the adapter.

  2. On your phone open up a tone generator. I like to use this site.

    Set the volume on the site to 100%, then press the transmit key on your radio

    This will transmit from your phone over the radio. Look at the black bar at the top of the radio - you'l want to adjust your phones volume so that the black bar at around 75% across the screen, but if its lower thats ok. My phone can only go as far as 50%.

    Once done adjusting stop the tone generator

  3. Now open the Robot36 app. This app lets you receive SSTV images

    In the bottom right hand side is a meter - it'll look like a grey bar initially

    Press and hold the "function" button - the bottom button on the left hand side of the radio. This opens the squelch on the radio so that the application can hear noise

    While holding the "function" button down adjust the volume knob on the radio so that the bar in Robot36 is about 75%. The most my phone would go is 50% and this still ok.

  4. Next we are going to turn on VOX. VOX is voice operated transmit, or simply put when the radio hears a noise it'll transmit.

    With VOX on any noise the phone makes will be transmitted onto the radio.

    Press and hold the function button, then press the menu button. Then release the function button. This should put you into the channel details menu. Select VOX from this menu and use the right arrow button to turn it on. Exit the menu by pressing menu.

    Remember to turn VOX off after your done using SSTV otherwise your radio will transmit on loud noises

  5. Your radio should now be ready to send and receive SSTV. In the next steps we'll run through using the software.

Sending SSTV

  1. Open the SSTV Encoder App. By default you'll be presented with a test image.

  2. Click in the center of the image and it'll allow you to enter some text. Type in your callsign here and click the tick

    This will place your callsign on the image. You can tap and drag on the text to move it around the image

  3. Pressing the "image" icon (the left most icon in the tool bar) will let you replace the image with one from your phone

  4. Using the kebab menu (three vertical dots on the right) you can select the SSTV mode. Robot 36 is a good option to select to start with.

  5. When your ready to send your image select the play button. Your radio should start transmitting (red status led) and your image will start sending.

Receiving SSTV

  1. Open the Robot36 App.

  2. Robot36 app will automatically detect the SSTV mode and will automatically start receiving a picture as soon as it hears the SSTV tones. You can force a specific mode by using the kebab menu (three vertical dots). You can press the save icon to save the image to your gallery

  3. To exit the app press the pause button before closing it, otherwise it will continue to run in the background.