[Elecraft] KX3 OSC Temp And Freq Drift Relationship?

[Mark Petiford]

RE:  The extended temp compensation is mostly about transmit frequency stability. It might make some difference in decoding PSK31 as the rig cools down, but I would expect that to be a smaller effect.

To elaborate a bit more on wunder's comment, it is about frequency stability as related to temperature changes.  The reason it appears to affect transmit more than receive is because the KX3 power amplifier transistors generate lots of heat during transmit, heating up the SI570 oscillator.  The SI570 also generates heat, but generates the same amount of heat during transmit and receive (it doesn't know the difference), so it tends to add to the heat during transmit, and slow the cool-down during receive.  The relatively poor heat rejection capability of the KX3's enclosure (designed for TFR, not heat rejection) figures into that mix as well.  So, fast frequency drift during transmit, slower drift during receive.

I've used SI570's for a number of years on my SDR projects, but have always had the luxury of being able to isolate them from the radio's final amplifier transistors, and any other heat source.  They have therefore been very frequency stable once their temperature levels off following power-up.  The tight packaging of the KX3 doesn't allow that.  From the reports so far, it looks like Elecraft's "look-up table" approach is pretty effective at compensating.

Mark
KE6BB