VHF Logger

VHF Logger started as a small experiment: building a simple online QSO logger with the help of Claude Code. It began basic and has been growing steadily ever since — and still is. Today it covers a full contest log, ON4KST chat, a live aircraft display with a prediction of when aircraft scatter becomes usable, and a watchlist you can build yourself or generate automatically from the stations currently logged in on ON4KST. Each of these windows/features can be individually enabled or disabled in Settings.

1. First-time setup

When you open the logger for the first time, Settings opens automatically. Fill in these fields:

Station identification

Address (used in EDI submission)

Station equipment (used in EDI submission)

2. Logging a QSO

Form mode — step-by-step example

The following example logs a QSO between OZ7Z (your station, JO44VW) and G3YDY (JO01FQ) at 17:15 UTC on 144 MHz:

1. Dato — leave empty for today, or type 260101 for a specific date. Press Enter.
2. Tid — leave empty for current UTC, or type 1715. Press Enter.
3. Call — type G3YDY and press Enter. If G3YDY is in your locator database, the Loc field fills automatically on blur.
4. RST S — your report to G3YDY. Type 59 (or leave 59 as default) and press Enter.
5. RST R — G3YDY's report to you. Type 57 and press Enter.
6. Nr S / Nr R — serial numbers, if enabled in Settings. Nr S is pre-filled from the running counter (editable). Nr R is required when serials are enabled — the QSO cannot be saved without it.
7. Loc — type JO01FQ and press Enter. The distance (720 km) is calculated and the QSO is saved.

Editing a logged QSO

Each QSO row has two buttons on the right:

QSO actions (× button)

The × button opens an action menu with three choices:

• Cancel — closes the menu without making changes
• Mark as dupe / Un-dupe — toggles the duplicate status (un-duped QSOs count in score even if the same callsign appears earlier)
• Delete — permanently removes the QSO from the log

One-liner mode

Enable under Entry mode → One-liner in Settings. Type everything on one line and press Enter. Tokens are order-independent — the logger recognises each by its format.

Important convention: the RST you send (your report to the other station) is marked with a sent marker after it — ' (apostrophe) by default. The RST you receive is written without the marker. The marker itself is configurable in Settings → Advanced → Sent marker (up to 2 characters) if you prefer something other than '.

Full format: CALL [HH:MM or HHMM] [SND-RST'] [RCV-RST] [NR] LOCATOR
Locator and callsign are the only required fields — everything else is optional.

Serial numbers in one-liner mode

When Serial numbers is enabled in Settings, you can glue a serial number directly onto the RST — no separate token needed. Whether it's a sent or received serial depends on the same marker convention used for RST:

The hint line shows Snt#: / Rcv#: as you type to confirm what was recognised.

Entering a custom time and date (one-liner)

To log a QSO with a time other than the current UTC time, type it in HH:MM or HHMM format (with or without colon) anywhere in the one-liner line, before the callsign — e.g. 17:32 G3YDY 57 JO01FQ or 1732 G3YDY 57 JO01FQ. The hint line confirms it is recognised: Tid: 17:32.

To log a QSO with a different date, fill in the small Dato YYMMDD field that appears below the input box (e.g. 260101 for 1 January 2026). Leave it empty to use today's date. The date field is not cleared between QSOs so you can log several QSOs with the same back-dated date without re-typing it. Press F3 to clear the date field together with the input.

Entering a custom time and date (form mode)

Form mode has a Dato YYMMDD field and a Tid UTC field at the start of the form. Both default to the current date and time if left blank. They are cleared automatically after each QSO is saved.

Locator autocomplete in one-liner

When you press Space or Enter after a callsign (or a partial callsign, 3+ characters), the logger looks it up in the locator database automatically. Nothing is inserted into the line yet — a picker with the matching candidates opens above the input field instead.

• Press Ctrl+X to insert the first candidate. Press it again to replace with the second, again for the third, and so on — wrapping back to the first once you've cycled through all of them.
• Arrow keys (↑ / ↓) + Enter, or a mouse click, work as an alternative way to jump straight to a specific entry.
• Press Esc to dismiss the picker without inserting anything.
• No match — space is inserted normally; type the locator yourself.

Duplicate warning

As soon as the typed callsign matches an already-logged QSO, the one-liner input turns red and a short beep sounds — in addition to the DUPLET text shown in the hint line below. Both cues clear automatically once you move past the callsign or clear the line.

Portable/mobile suffixes don't create a new station for duplicate purposes: OZ1DSK, OZ1DSK/P and OZ1DSK-P are all treated as the same call. Prefix-style calls like OZ/DL4MM are recognised as valid callsigns too.

Wildcard callsign lookup

Use ? as a wildcard for a single unknown character in a callsign. Press Space after the partial callsign to search the locator database:

A picker appears with all matches from the database. Select the correct station — the wildcard token in the input is replaced with the actual callsign and the locator is inserted automatically.

Prefix search also works without wildcards: type OZ7 and press Space to see all database entries beginning with OZ7.

Live search — replaces the log list

As soon as the last thing you're typing is 2 or more characters containing a letter, the QSO log table is temporarily replaced with every locator-database entry where that text appears — anywhere in the callsign or the locator, not just at the start. This is separate from the Space/Enter picker above: it updates on every keystroke, doesn't require a complete callsign first, and searches locator text too.

Matches you've already worked (logged in this session) are separated into their own narrow column on the left, so you can see at a glance who's still needed. Everything else fills the remaining 3 columns to use the panel's width. Both lists are sorted alphabetically by callsign, filling each column top-to-bottom before wrapping to the next. Each entry shows distance and QTF (bearing) after the locator, e.g. JO44WE · 182km 177° — same figures as the map/log, requires a home locator to be set in Settings. Click any entry to fill that call and locator into the input, same as picking from the Space/Enter picker.

Press Esc, clear the input, or move on to the next field (a space) to bring the log table back. If you were on a different tab (Watchlist/KST/Online), it switches you to Log list automatically so you can see the results.

Queuing the next QSO — /n

While logging a QSO you can note one or more upcoming stations using /n CALL anywhere in the line:

The hint line shows the queue as → G4SWX → SM5EPO while you type. After logging:

1. The first queued callsign is pre-filled (with locator from DB if available).
2. The remaining /n entries stay in the input so they are passed on when that QSO is logged.
3. When the last queued QSO is logged the input clears normally.

3. Score

The score is shown continuously in the bar below the top menu:

• KM pts — sum of distances for valid QSOs
• AVG — average KM pts per QSO (KM pts ÷ number of valid QSOs)
• ODX — the longest-distance QSO in the log: callsign, locator and distance
• WWL × 500 — points per unique Maidenhead square (4 characters). The 500 is the WWL bonus value from Settings (default 500 for NAC; set to 0 for IARU Region 1 contests, which have no locator bonus) — the label updates to match.
• Total = KM pts × band multiplier + WWL bonus

Worked example

You are OZ7Z (JO44VW) on 144 MHz and have logged three QSOs:

Score calculation:

KM pts  = 720 + 630 + 700 = 2050
WWL     = 3 unique squares × 500 = 1500
Total   = (2050 + 1500) × 1 = 3550

The band multiplier is ×1 for 144 MHz. Microwave bands get a higher multiplier:

4. EDI export / import

Click ↓ EDI to download your contest log in REG1TEST format (Tucnak-compatible). The file can be uploaded directly to vushf.dk.

Click ↑ EDI to load a previously saved EDI file back into the logger. If the log already contains QSOs, you're asked whether to Replace them or Merge the imported QSOs in — merge skips any QSO that's already logged (matched on callsign + date + time), so it's safe to re-import the same file without creating duplicates. Distances are recalculated from the locators using the current home locator setting; any QSO with a blank locator field in the file is looked up in the locator database instead.

Importing also updates your Contest start date / Contest end date (Settings) to match the date range of the imported QSOs, and your callsign to the file's PCall= field — so the sync date window (see §11) lines up automatically instead of pointing at whatever date was set before.

Filename: OZ7Z_144MHz_260506.edi

Each QSO line: date ; time ; call ; mode ; RST-sent ; nr-sent ; RST-rcvd ; nr-rcvd ; locator ; distance-km

Settings → Advanced → Local backup every N QSO automatically triggers this same download after every Nth QSO you log (0 = off), so you always have a recent backup on disk without clicking ↓ EDI yourself. Each auto-backup gets a _bkNNN suffix (current QSO count) so successive files don't overwrite each other.

5. Locator database

Import a text file with known stations for callsign autocomplete. One station per line:

G3YDY;JO01FQ
G4SWX;JO02RF
SM5EPO;JO89WK
OZ7Z;JO44VW;Allan

Supported formats:

• CALL;LOCATOR
• CALL;LOCATOR;NAME
• DATE;CALL;LOCATOR;NAME (Tucnak EDI style)
• Whitespace-separated: CALL LOCATOR …

A callsign may appear more than once with different locators (e.g. a portable station at different QTH). If there are two or more locators for the same call, a picker appears when you press Space in the one-liner or leave the Callsign field in form mode.

Click 📂 Load locator file in Settings. The database is stored in the browser and merged with any new file you load.

If you load or update the locator database after QSOs are already logged, click ↻ Recalc in the top bar to look up any missing locators for already-logged QSOs from the database, recalculate distances, and re-run the duplicate check for the whole log in one go.

6. Aircraft scatter

Aircraft scatter allows VHF/UHF QSOs over long distances via reflection from aircraft. Flight data is fetched via vushf.dk as a proxy — it tries airscatter.dk first and automatically falls back to OpenSky Network if airscatter.dk is unavailable. The active source is shown in the info bar below the map: 42 aircraft · airscatter.dk or 42 aircraft · OpenSky.

Adding stations to the Watchlist

Open ⚙ Settings and switch to the ✈ Watchlist sub-tab (next to General, top of the Settings panel). It has an add-row at the top and a list of your stations below — there is no fixed row count or upper limit.

1. Type a callsign and locator into the two fields, then click + Tilføj (or press Enter) to add the station to the list.
2. Each row in the list can be edited directly — click into the Kald or Lokator field and type; changes save automatically.
3. The checkbox on the left of each row controls whether that station is actively watched for scatter — the same checkbox state is shared with the live Watchlist tab (see below).
4. Click the ✕ button on a row to remove just that station.

To import a station list from a file, click ↳ Import file at the top of the Watchlist sub-tab. To clear all stations at once, click the red ✕ Ryd liste button — you will be asked to confirm.

Getting started with scatter

1. Click ✈ Planes in the top bar — aircraft within the search radius are now fetched every 10 seconds.
2. Open the ✈ Watchlist tab in the left panel (this is the live scatter view, separate from the Settings → Watchlist setup above).
3. Tick the checkboxes next to the stations you want to check scatter against. Use the header checkbox to select all at once.
4. The logger automatically shows which aircraft are in scatter position and when the next one arrives.

What does the watchlist show?

Scatter parameters

The scatter corridor angle and minimum aircraft distance are set automatically based on the selected band. You can adjust them manually in Settings:

Map overlays

• Zone — shows the yellow scatter corridor polygon on the map
• Lines — shows a green line between your station and the remote station during active scatter

7. ON4KST chat

The logger has a built-in client for the ON4KST VHF chat network. Use it to arrange skeds with other operators during a contest.

Connecting

1. Click the KST tab in the top-left panel.
2. Enter your callsign, password and the channel you want to join (e.g. 144 for the 144 MHz room).
3. Click Connect — incoming messages appear in the chat window.
4. Type a message in the input box at the bottom and press Enter to send.
5. Click Disconnect to log out.

The chat window is split in two: the top pane shows the full channel traffic, while a smaller pane below it — "Mine beskeder & svar til mig" — mirrors only the messages you sent and any lines mentioning your own callsign, so you can follow your own conversations without scrolling through a busy channel.

The browser asks for notification permission the first time you click Connect. If granted, a desktop pop-up appears whenever your own callsign is mentioned and the tab isn't currently visible — so you won't miss a sked request while looking at another window, without the pop-up stealing focus from wherever you're working.

Split view — KST above the QSO entry

For single-op use, enable Settings → Advanced → Split view: KST above QSO entry to dock a compact chat panel — with its own message box — directly above the QSO entry, so you can watch and reply to KST without switching tabs.

• Press F4 to jump keyboard focus between the KST message box and the QSO entry field. Whichever one currently has focus gets a highlighted border, so it's always clear which one you're typing into.
• Drag the top edge of the panel to resize it — the height is remembered.
• Use the filter dropdown in the panel header to narrow what's shown: All, Mine + mentions, CQ only, or Watchlist (only lines mentioning a call currently on your Watchlist).

Right-click — scatter sked from Watchlist

When a station in the Watchlist tab is also online on KST it shows a ·KST badge next to its callsign. Right-click the callsign to open a context menu with a pre-filled scatter sked message. Example:

G3YDY pls sked on 144.300 AP in 8 min

The frequency is taken from your active band and the time is the current scatter ETA. Edit the message if needed and press Enter to send it.

Online tab — all logged-in users

The Online tab (tab 4) shows all stations currently logged into the KST channel. Click Fetch active users to refresh the list. The list is filtered by distance — only stations within the configured maximum (default 1000 km) are shown.

Left-click any callsign — in the chat log, the "Mine" pane, the split-view panel, or the Online list — to instantly fill the message box with /cq G3YDY, ready to send. Right-click instead opens an editable popup pre-filled the same way, if you want to change the message before sending.

Sorting: click the Call, Lokator or km column header to sort the list by that field. Click the same header again to reverse the direction (ascending ↔ descending, shown by a ▲/▼ marker). Stations with an unknown distance always sort to the bottom.

Bulk-add to Watchlist by range

Below the header row of the Online tab is a + Tilføj til watchlist button with two range fields, "fra" (from) and "til" (to), in km. This adds every currently online station whose distance falls within that range to your Watchlist in one click — skipping stations already in the list or without a valid locator. Newly added stations are automatically checked as actively watched. Your home locator must be set in Settings for this to work.

8. Layout

• Drag the vertical divider between the log panel and the map to adjust the width.
• Drag the horizontal divider above the watchlist to adjust the map height.
• Switch between Log list, Watchlist, KST and Online using the tabs in the top-left.
• Don't use one of the tabs? Hide it: Settings → Advanced → Faner has a checkbox per tab. At least one must stay checked. If the tab you're currently on gets hidden, the view automatically switches to the first tab still enabled.
• Select a theme from the dropdown in the top-right:

  Theme	Description
  Dark	Very dark background (near-black). Map tiles are heavily dimmed. Best for operating in complete darkness.
  Dim	Softer dark background with slightly more contrast. Map tiles are a little brighter than Dark. Comfortable for extended use in low light.
  Warm	Dark background with an amber tint. Map tiles get a sepia filter. Easy on the eyes during evening sessions.
  Light	White background, standard bright mode. Map tiles are shown at full brightness. Best in daylight.

9. Keyboard shortcuts

10. Data and backup

The log is saved automatically in the browser's localStorage after every QSO — it survives browser restarts. Data is not deleted when the page is refreshed.

The log is stored per band — each band you select in Settings has its own separate storage key (e.g. zlog_log_144MHz). Switching bands loads that band's log instead of continuing the previous one, so QSOs from different bands never get mixed together, even across multiple browser tabs on the same computer.

To move your log to another computer: use the browser DevTools (F12 → Application → Local Storage) and copy the key for your band (e.g. zlog_log_144MHz) and zlog_settings.

11. Multi-machine sync

The logger can synchronise the QSO log in real time between two or more computers on the same operator setup — for example a desktop running the map and a laptop at the radio.

1. Click the 🔗 Net button in the top bar. When active it turns green.
2. Both machines see each other's QSOs within approximately 3 seconds.
3. New QSOs logged on either machine appear on the other automatically.
4. Clearing the log on one machine also clears it on the other.

The date window is set in Settings via Contest start date and Contest end date (YYMMDD). Both reset to today automatically whenever you click Clear log, so a fresh contest day naturally gets its own sync file — and both are set automatically from the QSO dates when you import an EDI file (§4). For a contest spanning more than one calendar day, widen Contest end date manually before you start.