Reading reception reports
A reception report tells you three things: how well you were heard, by whom, and where. What it does not do is tell you any of that in a way that survives naive comparison — a −8 dB report from one station and a +2 dB from another may well mean your signal was identical, and the difference sat entirely at their end.
What SNR actually measures
Signal-to-noise ratio is exactly what it sounds like: how far your signal stands above the background noise, expressed in decibels. Every 3 dB is a doubling, so the difference between −6 and 0 dB is a factor of four in power, not a small nudge.
Negative numbers surprise people. They should not: a negative SNR means the signal is weaker than the noise in the measurement bandwidth, and modern digital modes decode comfortably down there because they concentrate their energy into a narrow slice the noise is spread across.
What it means for a picture
Analogue SSTV degrades in direct proportion to SNR, which makes it unusually informative to look at:
| Roughly | What arrives |
|---|---|
| +10 dB and up | Clean picture, colours true, callsign banner crisp. |
| 0 to +10 dB | Visible speckle, perfectly readable, quite normal. |
| Around 0 dB | Heavy noise, subject recognisable, text marginal. |
| Below 0 dB | Fragments. You can tell someone transmitted; not much else. |
A digital picture mode behaves nothing like this — it holds perfect quality until it crosses its threshold and then delivers nothing. That cliff is the central trade discussed in analogue versus digital.
RSV, not RST
SSTV has its own report format. Where a voice contact exchanges RST — readability, strength, tone — a picture contact exchanges RSV:
- Readability, 1 to 5.
- Strength, 1 to 9.
- Video quality, 1 to 5 — replacing tone, which means nothing here.
595 is a clean picture from a strong station. 335 is a picture you can just about make out.
Why distance is a bad measure
The instinct is to read a long-distance report as a good signal and a short-distance failure as a bad one. On HF that instinct is close to backwards.
Your transmission leaves in two forms. The ground wave follows the earth and fades out within tens of kilometres. The sky wave goes up, refracts off the ionosphere and returns hundreds or thousands of kilometres away.
Between where the ground wave dies and where the sky wave lands there is a ring that receives neither. That is the skip zone, and it is why the station in the next county hears nothing while a station in another country copies you at 595. Nothing is wrong with your signal. The geometry simply excluded them.
The skip zone moves with frequency, time of day and ionospheric conditions, which is why the same two stations can work each other easily one week and not at all the next.
Comparing reports honestly
- Compare the same receiver over time. One station’s reports across several weeks tell you something real about your station. Two different stations on the same day tell you mostly about them.
- Local noise dominates. An urban receiver may sit ten or more decibels above a rural one before anyone transmits. Their −5 dB and a rural +5 dB can describe the same signal arriving.
- Antennas are not symmetric. A directional antenna pointed elsewhere will report you poorly regardless of how well you are getting out.
- Consistent damage is yours. If every report shows the same banding or distortion irrespective of distance, the problem is in your shack — start with levels and ALC.
Where these come from
On the Open Signal network, a report is filed automatically by the receiving station when it copies a picture: callsign, grid square, SNR, distance and the band it happened on. Nobody has to remember to send anything, which means the reports accumulate for marginal contacts as well as good ones.
Those records accumulate into something more useful than any single report: a picture of which paths actually work, from real measurements rather than propagation predictions.
Reception reports — FAQ
What does SNR in dB mean on a reception report?
It is the ratio between your signal and the background noise, measured in decibels within a reference bandwidth. Higher is better, and negative numbers are entirely normal — a digital mode can decode a signal well below the noise floor, which is what a negative SNR describes.
Why did a station 2000 km away copy me when one 50 km away did not?
The skip zone. On HF your signal leaves as a ground wave that dies within tens of kilometres, and as a sky wave that returns to earth hundreds or thousands of kilometres out. Between the two there is a ring where neither reaches — so the distant station hears you perfectly and your neighbour hears nothing.
What is an RSV report?
The SSTV equivalent of RST. Readability 1–5, Strength 1–9, and V for video quality 1–5 in place of tone. A picture that arrived clean and complete from a strong station is 595.
Why do two stations the same distance away report different SNRs?
Because SNR describes their receiving conditions as much as your transmission. Local electrical noise, antenna, and how much of the band's noise their receiver is listening to all move the number. Compare reports from the same station over time rather than between different stations.
More about Open Signal
Reports that file themselves
Every picture Open Signal copies generates a reception report with callsign, grid, SNR and distance — and every report on your own transmissions comes back to your operator page.