Decoding SSTV with an SDR — or no radio at all
The cheapest way into pictures on radio is not a radio. A twenty-pound dongle will pull SSTV out of the air, and a public WebSDR will do it for nothing at all from a browser, using somebody else's antenna on the other side of the country. Neither needs a licence, because neither transmits.
Route one: no hardware whatsoever
Public WebSDR and KiwiSDR receivers are real radios with real antennas, connected to the internet and shared. You tune them through a web page, and the audio comes back to your browser.
For SSTV this is close to ideal for a first attempt, because it removes every variable except the decoder:
- Find a public receiver covering HF, ideally one in Europe for Region 1 activity.
- Tune to 14.230 MHz, USB.
- Route the browser’s audio into your decoder.
- Wait. Pictures appear exactly as they would from your own radio.
Cost: nothing. Equipment: a computer. It is also the fastest way to prove your decoder works before you start blaming your antenna.
The honest caveat: the audio has been through a compression stage designed for listening rather than for data, so marginal signals decode slightly worse than they would locally. Strong ones are indistinguishable.
Route two: your own dongle
An RTL-SDR is a repurposed television tuner that presents raw radio spectrum to a computer. They cost about twenty pounds and they are genuinely capable receivers.
The catch worth knowing before you buy: the standard dongles start somewhere around 24 MHz, which is above every HF band where SSTV lives. To receive 14.230 MHz you need one of:
- A dongle with direct sampling support for HF.
- An upconverter that shifts HF up into the dongle’s range.
- A receiver designed for HF from the outset — more money, considerably less fiddling.
A plain dongle with no modification does cover 145.800 MHz, which means it will receive the ISS perfectly well. For a lot of people that is the better first project anyway: a stronger signal, a known schedule, and a picture from a spacecraft at the end of it.
The audio routing problem
This is the only genuinely awkward part, and it is the same regardless of which decoder you use. SDR software produces audio; the decoder needs to consume it; the operating system does not connect applications to each other by default.
- Windows: install a virtual audio cable — a software device that appears as an output to one program and an input to another. Set the SDR to output to it and the decoder to listen to it.
- Linux: PipeWire can route one application’s output to another’s input directly. No extra software, though the routing UI takes a minute to find. See SSTV on Linux.
- The lazy option: play the SDR audio through your speakers and let the decoder listen on the microphone. It genuinely works — the same approach as receiving without an interface — and it costs you some quality.
Note the irony: a rig with a built-in USB codec avoids this entirely, because the radio already presents itself as a sound card. The SDR route is cheaper and involves more plumbing.
Settings that matter
- Mode: USB. On every HF band. Wrong sideband decodes as noise.
- Filter width: around 3 kHz. Narrower clips the top of the picture tones; much wider just adds noise.
- AGC: slow, or off. Fast AGC rides the level through the transmission and puts banding across the image.
- Noise reduction: off. It is designed to remove steady tones, which is precisely what your picture is made of.
Why this is the best way to start
Every barrier to amateur radio — the licence, the radio, the antenna, the space, the money — sits on the transmit side. None of it applies to receiving.
An afternoon with a WebSDR and a decoder tells you whether pictures over radio interest you at all, before you have spent anything or sat an exam. If they do, the transmit side is still there afterwards.
SSTV with an SDR — FAQ
Can I decode SSTV without owning a radio?
Yes. Public WebSDR and KiwiSDR receivers let you tune someone else's radio through a browser, from anywhere. Point one at 14.230 MHz USB, route the browser audio into a decoder, and you have pictures with no hardware at all.
Will a cheap RTL-SDR receive HF SSTV?
Not on its own — the common RTL-SDR dongles start around 24 MHz, above the HF bands. You need either a model with direct-sampling HF support, an upconverter, or a receiver designed for HF. Those same plain dongles do cover 145.800 MHz, so they work for the ISS.
How do I get audio from the SDR into the decoder?
On Windows, a virtual audio cable — a software device that presents an application's output as another application's input. On Linux, PipeWire can route between applications directly. This is the one genuinely fiddly step, and it is the same step whichever decoder you use.
Is the picture quality worse through an SDR?
Not inherently. A decent SDR with a decent antenna decodes as well as a conventional receiver. What costs you quality is the audio routing — resampling, or a browser stream that has been compressed for bandwidth rather than fidelity.
More about Open Signal
Free to receive, whatever you receive with
Open Signal's RX version costs nothing permanently and does not care where the audio came from — a transceiver, a dongle or a browser tab. Point it at the sound and it decodes.