Low Temperature Performance of 433 mhz TX module

I am using one of the basic 433 mhz rf tx modules with a saw wave resonator to transmit outdoor temperature. I don't have a data sheet, but here is a link to the module

During a recent cold period I experienced a loss in range. I have found this data sheet which indicates a significant loss of power from 10C to 0C in a similar module.

Can someone please explain the mechanism behind the loss of power at lower temperature.

Is the oscillator shifting off frequency? If so, why? Is there some other temperature sensitive component?

This page shows the drift for a saw (and others) : News | Epson
I think it can be 30kHz, and a receiver can be 300kHz bandwidth, so it should not be a big problem. But if the frequency was already inaccurate, it can be a problem.

The saw oscillators can be bought with different temperature ranges, just like crystals. If a saw oscillator is specified for 0...70 degrees, what will happen below 0 degrees ? I don't know.

Do you use batteries ?
The current for the TX module are the same pulses as the data pin is toggled. So that could be pulses of 10mA.

I was not using batteries for power. The Arduino and TX module were powered at 5v from a USB wall wart. It is a regulated, switching power supply but maybe it has temperature sensitive components, and it was dropping in voltage.

I fixed the problem by separating the TX module power from the Arduino and using 9v for the TX module, and it's working like on a summer day. :sunglasses: