Re: LF: Osc drift (TCXO)

[MarkusVester@aol.com]

Hi,

In a message dated 11/29/02 7:03:23 PM GMT Standard Time, blanch@pncl.co.uk writes: 
> Layout of the IIG oscillator/synthesizer board is quite different from the 
> II, also the TCXO for the IIG is much bigger and a different part number. 
> The TCXO for the II is claimed to be a "numerically-controlled" type, that 
> for the IIG is not. Does anyone know the difference? I thought all tcxo's 
> were just thermistor-controlled varactor diodes in series with the crystal. 


 I think the idea of a numerically-controlled TCXO is having an internal ADC digitizing the NTC voltage, convert it in a calibrated nonvolatile lookup-table and then use a DAC for the varicap. Depending on digital resolution, this concept can be prone to a stepwise response to gradual temperature changes, possibly resulting in a sawtooth FM pattern.

73
Markus, DF6NM