User Guide

About EME Observer

EME Observer is a web application that provides an interactive map of 10 GHz Earth-Moon-Earth (EME) stations and enables seamless, single-click sked planning. It delivers high-resolution lunar ephemeris data and displays key signal path characteristics, such as libration rate, Doppler spread, and polarization offset, along with station profiles and statistical summaries.

Key features include:

• Station locations with details on power, antennas, QRZ.com links, personal websites, email addresses and station images (if available)
• One-click 10 GHz EME planner with visualizations of common moon windows and path characteristics
• Moon footprint and sublunar point plotting
• Moon distance, declination, and extra path loss—available daily and in 30-minute intervals
• Moon azimuth, elevation, topocentric libration rate, and Doppler spread at 10.368 GHz for both your and DX locations
• Relative libration rate, Doppler width (DXWidth), and spatial polarization offset (Dpol) between your and DX locations
• Accurate moonrise and moonset times for both local and DX stations
• Tabular station view with technical and contact details, including multi-field search
• Summary statistics covering power levels, antenna sizes, and DXCC distribution

EME Observer was originally developed for personal use—tailored to the pace of my lifestyle and portable 10 GHz EME operation, which I enjoy most. It is platform-independent and works equally well on desktop or mobile, making it easy to plan EME activity on the move. EME Observer is NOT a link budjet calculator. It will not tell you whether a QSO is possible but understanding the data it presents can significantly improve your chances.

Data and Accuracy

EME Observer performs astronomical calculations using the Astronomy Engine, built on the VSOP87 and NOVAS C 3.1 models. In certain areas, an optimized version of the Meeus algorithm is used to improve performance without noticeable reduction in precision.

All computations have been thoroughly validated against the Skyfield Python library, using the DE421 ephemeris from NASA Jet Propulsion Laboratory. EME Observer achieves positional accuracy within 1 arcminute (0.017°), fully meeting the precision needs of 10 GHz EME planning and analysis.

Doppler spread calculations are based on methods described by (J. Taylor K1JT, 2010), and spatial polarization offset (Dpol) follows the WSJT-X algorithm.

Station data is contributed by the community. To add or update a station, use this form. Please only add stations that have TX capability and achieved at least one 10GHz EME QSO.

Quick Start

EME Observer offers three display modes: Map View, Table View, and Statistics View.

Map View

Map View is the default view in EME Observer. When the page loads, "My Locator" and "DX Locator" fields are empty, and the date and time are set to the current UTC time, rounded to the nearest 30 minutes. You can adjust the date using the date picker or its arrow buttons, and change the time by moving the time slider. The plotted moon footprint updates dynamically in 30-minute intervals as the time slider is adjusted by the user. The position of the moon icon represents the sublunar point—the location on Earth where the moon is directly overhead.

Control Panel

The Control Panel in EME Observer includes time and date controls, QTH locator input fields for both your station and the DX station, and buttons to switch between Table View and Statistics View. It also provides access to the station data submission form, a link to this guide, and a Hide Panel button, which minimizes both the control panel and charts to improve map navigation on smaller screens.

Daily Moon Data Chart

When the page loads and no QTH Locator has been entered by the user, the Moon Data Chart is the only chart displayed. It shows geocentric (Earth-centered) moon data that does not depend on any station location. This chart covers a period of 30 days, with the X-axis representing calendar dates and shows:

• Moon Distance
• Moon Declination
• Extra Path Loss (relative to the minimum path loss at perigee)

The vertical black bar on the chart represents the chosen date and acts as a time marker. You can change the date using the date picker or its arrow buttons.

Each curve and its corresponding Y-axis are color-coded, as are the numerical values shown above the chart for the current moon distance, declination, and extra path loss. These values update in 30-minute intervals as you move the time slider.

My Location Chart

The My Locator Chart becomes visible once the user enters a valid 6-character QTH locator in the My Locator field. This chart displays data specific to the user's location, including:

• Moon Elevation
• Moonrise and Moonset Times
• Topocentric Libration Rate
• Doppler Spread at 10.368 GHz (equivalent to "Width" in the Astronomical data window of WSJT-X)

The X-axis represents time in 30-minute intervals, and the black vertical line serves as a time marker that updates as the user moves the time slider.

Each curve on the chart is color-coded to match its corresponding Y-axis, and the current values for moon elevation, azimuth, libration rate, and full limb-to-limb Doppler spread are shown above the chart in matching colors for quick reference.

DX Location Chart

The DX Locator Chart appears when a valid 6-character QTH locator is entered for the DX station. It shares the same layout and visual style as the My Locator chart.

When both charts are visible, users can compare Moon visibility for their own station and the DX station, helping to identify overlapping Moon windows for potential QSOs. The DX locator can be entered manually, or automatically by clicking a station marker on the map and then selecting the green Sked button next to the station’s locator.

Sked Chart

The Sked Chart becomes visible when valid 6-character QTH locators are entered in both the My Locator and DX Locator fields. It displays key signal path metrics for the common Moon window (sked) between the two stations (computed as vectors): Relative Libration Rate (Rel LR), Relative Doppler Spread at 10.368 GHz (DX Width), and Spatial Polarization Offset (Dpol).

As with the other charts, each curve and its corresponding Y-axis are color-coded, as are the numerical values shown above the chart. These parameters are defined as follows:

• Rel LR – Relative libration rate between the two stations
• DX Width – Relative Doppler spread at 10.368 GHz (equivalent to DXWid in WSJT-X)
• Dpol – Spatial polarization offset in degrees (equivalent to Dpol in WSJT-X)

Station Map and Station Profiles

The map displays 10 GHz EME stations using four distinct marker types:

• Home station (active) – a fixed-location 10 GHz EME station
• Home station (not active) – not active but known to QRV in the past
• DXpedition – a portable station operating outside its home QTH locator
• Silent Key – a station formerly active, now marked in memoriam

Clicking a marker opens an info window with the station profile. This includes the callsign, operator name, and QTH locator, along with a green Sked button for one-click sked planning. Where available, you will also see details such as antenna size, transmit power, website link, station photo, and a dedicated QRZ button for direct access to the operator’s QRZ.com page. The blue Email button opens your default email client with the station’s address pre-filled, making it easy to arrange a sked.

Table View

You can access the Table View by clicking the Table View button in the Control Panel. This mode presents a detailed, sortable, and customizable table of 10 GHz EME stations. Each row includes essential station information such as the callsign, QTH locator, DXCC entity, antenna type, transmit power, and any available notes. If contact information is provided, Email, QRZ, and Website buttons will also appear, allowing easy access to external resources or direct communication.

The table supports full-text search across all columns, making it easy to filter stations by criteria such as DXCC prefix, power level, antenna size or type, and more. You can sort by any column or narrow results with targeted queries to quickly find stations of interest.

Statistics

The 10 GHz EME Statistics view can be accessed from the Control Panel. It currently displays dynamic charts showing the distribution of stations by antenna size, transmit power, and DXCC entities. These statistics are automatically updated whenever station data is added or modified.

Mobile experience

EME Observer features a responsive design optimized for mobile devices, presenting all essential data in a compact, touch-friendly layout. The screenshots below show the interface as displayed on an iPhone Pro. On smaller screens, vertical scrolling is enabled for charts, allowing users to explore data easily while key controls remain fixed for quick access. The control panel can be minimized using the Hide Panel button, making it easier to explore the map, Moon footprint, and station profiles. One-click sked planning functions identically to the desktop version.

Use on Bands Other Than 10 GHz

While EME Observer is primarily designed for planning 10 GHz EME QSOs, many of its metrics and tools are also valuable for planning and evaluating activity on other EME bands. These include the Moon footprint, Earth–Moon distance, additional path loss, lunar declination, elevation and azimuth charts, libration rate, moonrise and moonset times, and polarization offset.

Please note that Doppler spread is calculated specifically for 10.368 GHz and is not directly applicable to other frequencies. Additionally, the effects of lunar libration are frequency-dependent and vary both qualitatively and quantitatively with the operating band.

A note on Spatial Polarisation Offset (Dpol)

For certain EME path geometries, the plot of the Spatial Polarization Offset may exhibit abrupt transitions, with the Dpol value rapidly changing sign near ±90 degrees (see the center and bottom plots in the figure below). The Dpol values displayed by EME Observer are consistent with those reported by WSJT-X. When instantaneous values from WSJT-X or the VK3UM EME Planner are plotted, similar abrupt transitions can be observed. For more details, see this discussion.