Total posts : 45366
Very likely certain capacitors and resistors in the transmitter are changing values in the cold. Unless they are “NPO” quality and 1 percent or less tolerance, the cold will change the values enough to change the sound of the transmitter. These components can also cause the transmitters master oscillator to drift off frequency which can cause the signal to change in a modern day digital style receiver.
The best way to test a transmitter for these affects is to spray specific components on the circuit board with “cold spray”. This substance is usually in a spray can and is used for TV repair. After warming the transmitter to operating temperature, open the case and spray components one at a time. Listen for signal changes. You will find the culprit.