A site about the radio listening hobby and my activities therein - longwave, mediumwave, shortwave, FM, and television DXing. A site about the radio listening hobby in all its forms, or at least the forms that interest me.

I am also a licenced amateur radio operator, callsign VE3LXL. Information about my amateur radio station is found on my station website.

Monday, 3 January 2011

SSTV on 20 Metres

One of the many transmission modes that radio amateurs can use on the HF bands is slow-scan television (SSTV). SSTV lets one transmit pictures using a narrow bandwidth signal, one narrow enough to fit in the 3 kHz legal bandwidth limits on the HF bands. The tradeoff is that low bandwidth means slow transmission and low resolution. In fact, it can typically take between 30 and 120 seconds to send a single frame. There is also no audio. So SSTV doesn't allow for the transmission of video. Instead, it is more like a slow slideshow, with pictures in SSTV mixed with talk between them in standard SSB.

Anyone with a shortwave receiver that supports SSB and a computer with a soundcard can decode SSTV signals. I use free software called MMSSTV for this. MMSSTV also generates SSTV signals that can be sent to a radio transmitter, of interest if you're a radio amateur that wants to try out this mode.

Radio amateurs using SSTV tend to stick close to a small range of frequencies so they can find each other. On the 20 metre band they're usually found around 14230-14240 kHz.

Today I had MMSSTV running, monitoring 14230 kHz to see what would pop up. I caught two stations operating in SSTV:
  • WB5UXC, Pearlington MS at 2200-2220 UTC with a fair signal. He was in contact with KA0UNB (who wasn't visible to me) and with an N9 station. At 2219 he was calling CQ using a special CQ image.
  • XE1RK, Mexico City (D.F.), Mexico at 2221-2230 with a good signal. This station answered WB5UXC's CQ call and they swapped pictures and talked in SSB. Fairly clear picture.
It may just be a slow slideshow but I think it's great that amateurs can transmit a type of television signal on shortwave.

Note that SSTV is different from ATV (Amateur television), where amateurs transmit standard broadcast quality television signals. ATV allows for full video with audio, but is restricted to the UHF bands because of the wide bandwidth needed.

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