TCXO-9 frequency stability modification Yaesu

This 10-minute project increases the short term frequency stability for Yaesu FT-817, FT-857D and FT-897D transceivers with the TCXO-9 reference oscillator unit for digital modes like FT8 and JT65.

English: when I was making my first QSO’s with FT8 on the 2-meter band with my FT-897D, I was disappointed by the short term stability. After each TX-period, I could see all received signals drifting like 10 – 20 Hz in 30 seconds at the 2-meter band. It was annoying to see, and it made me wonder if my signal would be decodable with this amount of drift. The problem is related to the airflow that goes over TXCO-9 reference oscillator unit when the blowers go on. Simpy isolating the TCXO unit from this airflow by packing it with polystyrene packing material decreased the frequency drift to unnoticeable values!

Nederlands: tijdens het maken van FT8 QSO’s op de 2-meter band met mijn FT-897D, viel het me op dat alle ontvingen signalen langzaam verschoven in frequentie met zo’n 10 tot 20 Hz per 30 seconden als ik een zend-periode achter de rug had. Ik vond het hinderlijk en vroeg me af of dit geen FT8 gevoeligheid zou kosten. Het probleem van het driften (slechte korte termijn stabiliteit) wordt veroorzaakt door de luchtstroom over TCXO-referentie oscillator als de blowers aan gaan. Ik heb de TXCO-9 ingepakt met polystyreen verpakkingsmateriaal en hiermee was de drift verdwenen!

73!

Thom PA9T

The TCXO-9 crystal oscillator


Block the vent-holes on the back of the FT-897D transceiver with polystyrene or tape or whatever. The TCXO-9 crystal oscillator is wrapped with polystyrene too.

Completely isolate the crystal oscillator unit from any airflow by wrapping it.