PhosphorSSTV

PhosphorSSTV decodes Slow Scan Television (SSTV) signals in real time using your iPhone's microphone.

SSTV has been the amateur radio image transmission mode since the 1960s. From cold-war era picture transmissions to International Space Station passes, SSTV encodes images as audio tones between 1200–2300Hz. Each scanline is a sweep through frequency space, painting pictures one line at a time across the HF bands.

Hold your phone near a shortwave radio tuned to an SSTV signal — or play a recording — and watch the image build scanline by scanline on an authentic phosphor CRT display, just like the original SSTV monitors.

No internet connection required. No external hardware. No account. Just your iPhone and a radio.

TEN SSTV MODES

• Scottie S1, S2, DX — the most widely used SSTV modes on HF worldwide
• Martin M1, M2 — popular across European SSTV activity
• Robot 36, 72 — YCbCr colour modes, used by the ISS during special events
• Robot 8, 12, 24 BW — fast greyscale modes for text, diagrams, and low-bandwidth conditions

REAL-TIME DECODING

• Progressive scanline rendering — the image builds top to bottom, just like a real SSTV monitor
• VIS code detection automatically identifies the transmission mode
• Sync-aligned slant correction eliminates timing drift for straight, clean images
• Hilbert transform FM discriminator for accurate frequency-to-pixel conversion

SIGNAL ANALYSIS

• Live FFT spectrum display shows the full 0–4 kHz audio band
• Scrolling waterfall reveals the SSTV signal structure in real time
• SSTV band markers at 1200 Hz (sync), 1500 Hz (black), and 2300 Hz (white)
• Input gain control from 0.1× to 20×

IMAGE LOG

• Decoded images saved automatically with thumbnails
• Full metadata: mode, timestamp, duration, VIS detection status
• View full-size, share, or delete
• Swipe to delete, tap to view detail

AUTHENTIC CRT AESTHETIC

• Green and amber phosphor display themes
• Scanline overlay, vignette, and glow effects
• Monospaced terminal typography throughout
• The same retro aesthetic as our PhosphorRTTY and PhosphorCW apps

WHERE TO FIND SSTV

• 20m band: 14.230 MHz USB — primary worldwide SSTV frequency
• 80m band: 3.845 MHz LSB
• 40m band: 7.171 MHz LSB
• ISS: 145.800 MHz FM during special SSTV events
• Or search YouTube/archive.org for SSTV audio recordings to decode

PRIVACY

PhosphorSSTV makes zero network requests. No accounts, no tracking, no analytics, no ads. Microphone audio is processed entirely on-device and is never recorded or transmitted. See our full privacy policy on our support page.

ABOUT SSTV

Slow Scan Television was developed in the late 1950s as a way to transmit still images over voice-bandwidth radio channels. Unlike fast-scan television (broadcast TV), SSTV takes seconds to minutes per image, encoding pixel brightness as audio frequency. The 1200 Hz sync pulse marks each line boundary, black is 1500 Hz, and white is 2300 Hz. Every pixel in between is a precise frequency in that range. Amateur radio operators worldwide still use SSTV daily on the HF bands, and the International Space Station periodically transmits commemorative images that can be received with nothing more than a handheld radio.