https://rfcorner.in/tags/145-mhz/Recent content in 145 MHz on Dhiru's NotebookHugoenWed, 08 Jul 2026 00:00:00 +0000https://rfcorner.in/posts/vhf-aprs-beacon-ideas/Wed, 08 Jul 2026 00:00:00 +0000https://rfcorner.in/posts/vhf-aprs-beacon-ideas/<p>This is an early design sketch of VHF (2m - 145 MHz) APRS beacons that are small and can be placed in vehicles like ambulances or fire trucks.</p> <h2 id="key-points">Key Points</h2> <ul> <li> <p>Si5351 module powered by the usual 25 or 26 MHz 0.5 ppm TCXO.</p> </li> <li> <p>Si5351 generates 145 MHz <code>Two-Tone APRS</code> RF output directly! Using an Si5351 for APRS (Automatic Packet Reporting System) transmission via FSK (Frequency Shift Keying) allows us to generate highly accurate AX.25 packets directly at the RF frequency (e.g., 144.390 MHz), eliminating the need for a separate modulator and VCO.Since APRS typically uses AFSK (Audio Frequency Shift Keying) fed into an FM transmitter, generating FSK with an Si5351 means directly shifting the carrier frequency or the VFO instead of modulating an audio tone.</p>