The video demonstrates a procedure to measure the actual keying speed (dit/dah length) of a Kenwood TS-890 transceiver against its internal "words per minute" setting, leveraging the relationship $\text{Unit Length (s)} = 1.2 / \text{WPM}$. The author previously found discrepancies in other radios (KX2, TR45). The measurement is performed using a TinySA Ultra spectrum analyzer set to zero span mode, triggering on the transmitted pulses while the radio transmits into a dummy load. When set to 20 WPM, the measured unit interval is found to be $60.2 \text{ ms}$, confirming that the TS-890's setting is accurately implemented ($1.2 / 20 = 0.060 \text{ s}$). The procedure serves as a validation technique for Morse code timing accuracy in transceivers.
Validating Kenwood TS-890 Keying Speed Accuracy
0:00:04 Purpose: To check the accuracy of the keying speed setting (WPM) on a newly acquired Kenwood TS-890, comparing it to prior tests on a KX2 and TR45 which showed slight calibration errors.
0:00:41 Key Formula: The relationship between unit length ($\tau$, in seconds) and Words Per Minute (WPM) is $\tau = 1.2 / \text{WPM}$. For $20 \text{ WPM}$, the expected unit interval is $60 \text{ milliseconds}$.
0:01:14 Setup: The radio is set to transmit on $14.030 \text{ MHz}$ into a dummy load to prevent stray RF interference from the analyzer picking up signals.
0:01:40 Measurement Tool: A TinySA Ultra spectrum analyzer is used in zero span mode, centered at the transmission frequency, with an acquisition time set to $200 \text{ ms}$.
0:02:44 Triggering: The analyzer is configured to trigger on the transmitted pulses (level set to approx. $-80 \text{ dBm}$) to stabilize the display.
0:03:16 Measurement Technique: Markers are set on the pulse trace; Marker 1 is placed near the beginning ($-3 \text{ dB}$ point), and Marker 2 (delta marker) is placed near the end of the pulse at the same relative vertical level.
0:04:24 Result: The measured pulse width (unit interval) is $60.2 \text{ milliseconds}$. This confirms the TS-890 accurately implements the requested $20 \text{ WPM}$ setting.
0:04:40 Conclusion: The video successfully demonstrated using the spectrum analyzer in zero span mode for precise timing measurements of radio keying signals.