What is WSPR: The Ham Radio Tool That Maps Where Your Signal Goes

Every ham has wondered where their signal really goes once it leaves the antenna. WSPR, short for "Weak Signal Propagation Reporter," is a digital mode that answers that question using tiny low power beacons and a worldwide network of listeners. It turns your normal HF rig into a propagation test tool so you can see, in hard data, how far your station reaches on different bands, times of day, and antennas.

On the air, a WSPR transmission looks like a whisper. It typically runs at one or two watts, occupies only a tiny slice of spectrum, and lasts just under two minutes. Inside that transmission is your callsign, grid square, and transmit power in dBm. Because the mode uses heavy error correction and very narrow decoding, stations can often copy you when your signal is 20 to 30 dB below the noise floor.

Each time you transmit, any WSPR-capable receiver that decodes you uploads a "spot" to a central database such as WSPRnet. After a few cycles you get dots on a map showing where you were heard, at what signal to noise ratio, and at what time. Leave it running for an hour and you suddenly have a propagation picture that would have taken days of QSOs to collect manually.

What exactly is WSPR doing on the air?

WSPR is part of the WSJT-X family of digital modes. Like FT8, it trades speed and readability for extreme weak signal performance. A single WSPR message is 162 symbols long and takes 110.6 seconds to send. All stations start transmitting on even UTC minutes, which means everyone is synchronized when they decode. The payload is small: your callsign, four character Maidenhead grid, and transmit power. That’s it. No long exchanges, no macros, just a steady beacon.

How WSPR turns your rig into a propagation probe

You don’t need a special "WSPR radio" to get started. Most hams run WSPR from WSJT-X on a computer, connected to the same HF rig they use for FT8 or PSK. Once you set the band and power level, you simply let it beacon every couple of minutes while the software logs both your transmissions and anything you hear from others. The result is an automatic, shared propagation experiment with thousands of stations worldwide.

• Step 1: Install WSJT-X, set your callsign and grid, choose the WSPR mode, sync your computer clock, and pick a WSPR frequency that fits your local band plan.
• Step 2: Set your radio to a low, safe power level, verify your antenna and SWR look reasonable, then let the station beacon for 15 to 30 minutes on a single band.
• Step 3: Check sites like WSPRnet or other mapping tools to see where your signal was heard, compare bands, and repeat the test with different antennas or power levels.

How WSPR compares to normal on-air activity

It’s tempting to think of WSPR as "just another digital mode," but it behaves very differently from common modes like FT8. There’s no back and forth exchange, so you never get a classic signal report from another operator. Instead, you get a statistical picture of where you could be making contacts if you switched to a conversational mode. WSPR is closer to a scientific instrument than a social mode, which is why it pairs nicely with more traditional operating on HF.

• Compared to FT8, WSPR is much slower but dramatically more sensitive. You trade rapid QSOs for the ability to see paths that are barely hanging on, especially at night or on the low bands.
• Compared to traditional beacons, WSPR is more flexible. Any station can beacon on many bands without dedicated hardware, and reports are automatically collected into online maps.
• Compared to simply calling CQ, WSPR removes the human factor. You’ll see where your signal reaches even when nobody happens to be tuning the dial or answering calls.

Understanding your station’s performance from WSPR maps

Once you start looking at WSPR spots, patterns jump out quickly. On 40 meters you might see strong regional coverage in the evening with a few long hops at sunrise. On 20 meters the same station could be hopping across the ocean all afternoon, then go quiet at local midnight. Because each spot includes SNR, you can see when a band is barely open versus wide open, and how that lines up with grayline, solar conditions, and your local noise floor.

These maps are also great for antenna comparisons. Run WSPR for half an hour on your dipole, then half an hour on a vertical, at the same power on the same band. If one pattern shows stronger DX but weaker local coverage, you’ve just confirmed the tradeoffs you might have guessed at from theory or modeling. Pair that with the antenna ideas over on the Antennas page and you can iterate on your station with real data instead of guesswork.

Practical WSPR tips for everyday hams

Because WSPR is slow and mostly automatic, it’s easy to either overuse it or forget to use it when it would really help. A little planning makes it a powerful tool instead of just background noise. Treat each WSPR session as a mini experiment with one clear question, like "Does my new 20 meter vertical beat the old wire on long path?" or "What band gives me the best coverage into the next state for emergency work?"

1. Pick one variable at a time. Keep power, band, and time of day the same while you change antennas or locations. Run enough cycles to get several dozen spots before you decide what "better" looks like.
2. Stay legal and courteous. Use the proper WSPR frequency segment for your region, respect band plans, and verify that your rig is actually transmitting the power level you claim in the software.
3. Try receive-only experiments. A small SDR tied to a simple wire can run WSPR receive 24/7, building a long term picture of your local noise and band openings. The SDR section has ideas for low cost setups.