FMT Test Transmission Format

FMT Test Transmission Format

Transmission Flow

Initial QST → Cycle start → Pulse → Carrier → Short QST → repeat (×6) → Sign-off

• Initial QST: 2 minutes
• Cycle (×6): Pulse 60 s → Carrier 60 s → Short QST ~12 s
• Final cycle ends with: FMT TEST DE SN0FMT SK

Overview

• Fixed duration of 15 minutes
• Start aligned to a published UTC time
• Deterministic internal structure
• Fixed frequencies; no retuning required for CW carrier measurements

Signal Modes and Frequencies

FMT test transmissions use two closely spaced RF frequencies and two different emission modes. This is intentional and designed to simplify receiver operation during measurements.

Important: The frequencies shown below (14 053 000 Hz / 14 052 000 Hz) are examples for clarity. Actual contest frequencies will be published for each event and may differ.

• CW identification and carrier block (example): 14 053 000 Hz in CW
• Pulse block (example): 14 052 000 Hz in USB

The pulse block is modulated with a 1 kHz tone and transmitted as a deterministic three-pulse burst.

The pulse signal is transmitted in USB at a frequency 1 kHz below the CW carrier frequency. This allows stations focused on carrier frequency measurement to remain tuned to the CW carrier frequency.

Initial QST

Each transmission starts with a 2-minute CW identification phase used for tuning and confirming reception. 

QST DE SN0FMT TEST FMT

Measurement Cycles

After the initial QST, six identical measurement cycles are transmitted. Each cycle lasts about 135 seconds and includes: 

• Pulse signal (60 seconds)
• Unmodulated carrier (60 seconds)
• Short CW identification (about 12 seconds)

FMT TEST DE SN0FMT

Final Sign-off

In the final cycle, the CW identification serves as the sign-off: 

FMT TEST DE SN0FMT SK

Timing and Calibration

All timing is derived from the published UTC start time and the fixed transmission structure. Receiver-side timing offsets are determined during separate calibration sessions and applied during result processing. 

Frequency Usage

The carrier and pulse signals are transmitted on two fixed, closely spaced frequencies. No frequency changes occur within a given signal type.

• CW identification and carrier measurements use the published CW carrier frequency
• Pulse measurements use the published USB frequency, which is exactly 1 kHz below the CW carrier frequency

This structure ensures repeatable measurements while keeping receiver operation simple and predictable.

What Is Measured

FMT measurements consist of three independent components. Each of them must be evaluated separately.

1. Pulse Burst (Pulse Duration)

The pulse signal is transmitted as a pulse burst. The first two pulses and the pauses between them are reference signals and are identical to those used during calibration sessions.

The measured value is the duration of the third pulse. The same measurement method should be used consistently for all cycles.

2. Offset Relative to 1PPS (Time Measurement)

The start of the first pulse in the burst has a fixed offset relative to the transmit-side 1PPS reference. This offset is one of the primary quantities to be measured.

We compare the received burst start to our local 1PPS, then apply receiver delay correction determined in calibration.

This station-specific delay is determined during calibration sessions, where the pulse burst starts exactly at the 1PPS boundary and has no intentional offset. The measured delay is stored as a constant and applied as a correction during contest data processing.

3. Carrier Frequency Measurement

During the carrier block, participants measure the carrier frequency independently from the pulse measurements.

The carrier is transmitted continuously for 60 seconds to allow averaging and high-resolution frequency estimation. The highest precision achievable by the receiving setup should be used.

Summary

• Pulse burst → duration of the third pulse
• First pulse start → offset relative to transmit-side 1PPS
• Carrier block → precise carrier frequency

Example of burst signal measurement and 1PPS offset

The image shows an example of a pulse burst measured by an FMT contest participant.

According to the FMT rules, one of the main tasks is to determine the burst start offset, specifically the offset of the first pulse relative to the 1PPS reference signal.
This type of measurement in FMT is referred to as 1PPS offset.

In the presented example, the first pulse starts 20 ms after the rising edge of the 1PPS signal.

Components of the measured offset

The measured offset is not the final result.
It always includes several components:

• the local delay of the participant’s receiving chain (antenna, receiver, filtering, digital processing, measurement equipment);
• the signal propagation delay from the transmitter to the receiver;
• any actual offset introduced at the transmitter side.

In this example:

• the receiver chain delay is 4 ms;
• the signal propagation delay is 8 ms.

The total system delay is therefore:

4 ms + 8 ms = 12 ms

Calculation of the correct 1PPS offset value

To obtain the correct result, the total system delay must be subtracted from the measured offset:

20 ms − 12 ms = 8 ms

This value (8 ms) is the correct 1PPS offset and must be entered by the participant in the result submission form on the FMT portal.

Requirement for receiver calibration

Correct measurement of 1PPS offset is not possible without prior calibration of the participant’s receiving system.

Calibration is performed during dedicated sessions where:

• the transmitter generates the pulse burst without any intentional offset, fully synchronized to 1PPS;
• the start of the first pulse at the transmitter coincides with the 1PPS edge.

Under these conditions, the offset measured by the participant represents only the delay of their own receiving chain.
This value is recorded and later used as a fixed correction when measuring 1PPS offset.

Importance of the pulse burst structure

The standardized pulse burst used in FMT is a critical element of the measurement process.

The burst structure:

• provides an unambiguous reference for burst start detection;
• enables reliable alignment of the first pulse to the 1PPS reference;
• contains internal timing elements with fixed parameters;
• allows verification of measurement stability and repeatability.

Pulse duration measurement

The image also highlights the third pulse in the burst, whose duration must be measured as part of the contest.

The timing of the first two pulses and all pauses between pulses are fixed constants, defined by the signal specification, and must not be measured or adjusted by participants.

Only the duration of the third pulse is subject to measurement, using the recommended signal edge processing methodology.