Getting Started with Flwrap: Error-Free File Transfers Over Amateur Radio

Flwrap is a specialized computer application used by amateur radio operators to encapsulate, compress, and transfer files with guaranteed integrity over the air. Part of the ⁠W1HKJ NBEMS (Narrow Band Emergency Messaging System) suite, it allows you to send text, images, or binary data (like spreadsheets) to one or many stations, ensuring the receiver gets an exact, error-free copy via checksum verification. Core Functions of Flwrap

Encapsulation: Wraps files in a standard “wrapper” that includes a checksum for error detection.

Compression: Automatically compresses files to reduce the transmission time over slow radio links.

Verification: Upon receiving, Flwrap checks the file’s integrity; if a single bit is wrong, the checksum fails, preventing the extraction of a corrupted file. Getting Started: The Workflow

To use Flwrap effectively, you typically use it alongside a modem program like Fldigi. Description 1. Wrap Drag & Drop

Drag the file you want to send onto the Flwrap desktop icon or the “Drop file here” box in the app. 2. Encapsulate Output File

Flwrap creates a new file with a .wrap extension (e.g., file.wrap) in the same folder as the original. 3. Transmit Insert into Fldigi

Open Fldigi, click “Insert file,” and select your .wrap file. Fldigi will convert it to base64 text for transmission. 4. Receive Capture Stream

The receiving station’s Fldigi captures the transmission and saves it into the NBEMS/WRAP/recv folder. 5. Unwrap Final Extract

The receiver drags the incoming .wrap file back onto their Flwrap icon. If the checksum matches, the original file is extracted. Key Performance Tips

File Size: Over HF radio, a typical rule of thumb is 1 minute of transmit time per 1 KB of file size. For FM repeaters, keep files under 2.5 KB to avoid timing out the repeater.

Format: Transmissions appear as a stream of random alphanumeric characters (Base64 encoding) in the Fldigi transmit pane.

Compression: Always enable the compression option in Flwrap settings to minimize “time on air”.

While ⁠FLAMP is often preferred for larger files or “multicast” situations where you might need to re-request missing blocks, Flwrap remains a simpler, more direct tool for sending small, critical files where the whole file must be perfect or nothing at all. Getting Started with Fldigi – Including Flmsg and Flwrap