Echo SNR Measurement

Station Tab — location and frequency

In the Station tab at the top of the window, enter your Maidenhead grid locator (e.g. FN42) and verify that the latitude and longitude fields update automatically. Enter your operating frequency in MHz (e.g. 1296.100). If you use a transverter, enter the IF offset in the XV offset field so that CAT frequency commands are correct. Set your elevation above sea level in metres.

PTT Configuration

Select your PTT serial port from the PTT port drop-down and choose RTS or DTR to match your interface. If you will use CAT PTT instead, skip this field and configure the CAT tab (Step 4).

Set the Audio delay value. This is the time between the PTT signal going active and the first audio sample being transmitted. A value of 200 ms is a safe default; reduce it only if you have measured the actual delay on your PC. The delay cannot be zero — some intrinsic audio pipeline latency is always present.

Audio Devices

Click Audio Devices… and select your sound card input and output from the drop-down lists. If you have only one sound card, leave both set to System Default.

Set the Audio Rx/Tx frequency. This is the audio tone frequency used both for transmitting and for locating the echo in the received audio. The default of 1500 Hz works well for most stations and is the same default used by WSJT-X.

CAT Control (optional but recommended)

In the CAT Control tab, select your rig model, port, and baud rate, then click CAT Connect. Once connected, you can enable Doppler shift RX to have the program automatically command the radio to track the Doppler-shifted echo frequency (similar to WSJT-X's “Fake It” mode), and enable PTT via CAT to use the CAT connection for transmitter keying instead of the serial RTS/DTR line.

Icom radios require the correct CI-V address in hexadecimal.

Doppler Correction — Audio Tracking

Check the Moon information bar. The current Doppler shift and a suggested RIT setting are displayed there. For most stations the simplest approach is audio tracking:

• If the Doppler shift is within approximately ±750 Hz, enable Audio tracking in the Moon bar. The program will automatically adjust its echo analysis window to follow the Doppler-shifted echo without touching the radio frequency.
• If the Doppler is outside that range, use your radio's RIT to bring the echo into the ±750 Hz window, then enable audio tracking. The Transfer RIT button copies the program's recommended RIT value into the RIT entry box; you must also set the same value manually on your radio.

Set Audio Levels

Click Tune to transmit a continuous 1500 Hz tone without starting a measurement sequence. Adjust your PC output volume and radio drive until you reach the desired RF output. Start low and increase gradually. While tuning, watch the input level meter:

• Green — good level.
• Yellow — level is high; reduce PC microphone gain or radio RF gain.
• Red — clipping; reduce immediately.

Click Stop when done.

Start the Echo Sequence

Click Echo Start. The program will transmit the tone for a period calculated from the current moon distance, then switch to receive and listen for the echo. The cycle repeats automatically.

After the first echo, the four SNR readouts in the SNR panel update:

• Last echo — SNR of the most recent single echo.
• Running average — power-domain accumulation of all echoes since the last reset.
• SEM — standard error of the mean of individual echo SNRs.
• Perigee equiv — the running average corrected to what the SNR would be if the Moon were at perigee distance.

The averaged echo spectrum plot updates after each echo. Click Reset avg to restart the accumulation without stopping the sequence.

Stop and Review

Click Echo Stop to end the sequence. If Save audio was checked, each echo has been saved as a WAV file in a dated subdirectory. These files can be reprocessed at any time with the EME Batch SNR Analyser.