Receive SSTV with no interface and no cables
Every guide to getting started with pictures on radio begins with a shopping list. It does not have to. If you own a radio that covers 14 MHz and a laptop, you can be decoding pictures in the next ten minutes with nothing between them but the air in the room — and no licence, because listening needs none.
Why this works at all
An SSTV signal, by the time it comes out of your radio, is just sound. The whole picture is encoded as a tone sweeping between roughly 1500 and 2300 Hz — comfortably inside the range of any microphone built for human speech.
The decoder does not care how the sound reached it. A cable is cleaner than a microphone, but the microphone genuinely works, and a picture decoded across a quiet room is indistinguishable from one decoded through copper.
Ten minutes, start to finish
- Tune the radio to 14.230 MHz USB and leave it. Upper sideband on every band, including 40 and 80 metres.
- Put the laptop next to the radio’s speaker. Not touching it — a foot away is fine and reduces the chance of the fan being the loudest thing in the recording.
- Set the radio’s volume to a normal listening level. Loud does not decode better; it distorts.
- Turn off every microphone enhancement in the operating system. This step is not optional — see below.
- Start the software, select the built-in microphone as input, and wait.
When a transmission starts, the decoder reads the VIS header, works out which of the six SSTV families is arriving, and paints the picture line by line as it comes in. You do not have to identify the mode yourself.
The step everyone skips
Modern operating systems assume any microphone input is a human voice on a call, and process it accordingly. Every one of those processes is hostile to SSTV:
- Noise suppression identifies a steady tone as background noise — which is exactly what an SSTV picture is — and removes it.
- Automatic gain control rides the level up and down through the transmission, which is precisely the distortion you are trying to avoid.
- Echo cancellation subtracts what it thinks is feedback, and takes parts of the picture with it.
On Windows these live under the microphone’s properties, usually on an “Enhancements” or “Signal Enhancement” tab. Disable all of them. On Linux the equivalents are usually in the PipeWire or PulseAudio configuration — there is more in SSTV on Linux.
What it actually costs you
Being honest about the compromises, because they are real:
- Room noise gets in. Conversation, traffic and a laptop fan all land in the same audio as the picture. Marginal signals that a cable would have decoded will fail.
- You cannot transmit. There is no PTT and no transmit audio path. This is a receive-only arrangement, which is the correct place to start anyway.
- Levels are awkward. You are setting them with a volume knob and the distance between two objects on a desk.
The cheap upgrade
Before buying an interface, try a 3.5 mm audio cable from the radio’s headphone or line-out socket to the laptop’s microphone or line-in socket. A few pounds, and it removes the room from the equation entirely.
It still gives you no PTT and no galvanic isolation, so it is a receive-only solution too — but it is a large jump in decode quality for almost nothing. When you want to transmit, that is the point to read sound-card interfaces properly.
Receiving without an interface — FAQ
Can I receive SSTV without any interface at all?
Yes. SSTV is ordinary audio in the 300–3000 Hz range, so a radio's speaker and a laptop's built-in microphone are enough to decode pictures. It is how a great many operators start, and it costs nothing.
Do I need a licence to receive SSTV?
No. In the UK, listening to amateur transmissions requires no licence. A licence is required to transmit, which is a different question and a different page. Receiving is open to anyone with a radio.
Why does my laptop microphone decode so badly?
Usually because the operating system is trying to help. Noise suppression, echo cancellation and automatic gain control are designed for speech on video calls, and all three actively destroy SSTV tones. Turn every audio enhancement off before blaming the radio.
When should I buy a proper interface?
When you want to transmit, or when room noise is costing you pictures you would otherwise have decoded. A 3.5 mm audio cable is the cheap intermediate step and fixes most of the quality problem; a proper isolated interface adds PTT keying and stops RF and ground loops causing trouble.
More about Open Signal
Receiving is free, permanently
The receive-only version of Open Signal costs nothing and always will. Listening is how the hobby starts, and nobody should be shut out of it by a licence fee.