Microwave repeater tower antenna heaters

About 45 years ago I had a job servicing microwave towers. About 500 ft up were the reflectors, antenna, wave guide. Frost was a problem in winter so heaters were set to come ON at 40 degrees F and stay on down to about -18 degrees F where heaters turned OFF. Below -18 heaters were not needed. I was told frost and ice will not freeze below a certain temperature that is why heaters turn OFF at a certain low temperature. I don't remember that exact below freezing temperature that was too long ago. -14 and -18 come to mind? The story I was told, when it gets very cold humidity in the air freezes with no humidity in the air frost can not freeze to the microwave surfaces.

Winter is here I have had frost on my vehicle windows every morning until we had -17 several weeks ago and -20 this morning there was no frost or ice on the window. Today when I saw no frost & no ice on window at -20 it reminded me of the microwave tower.

I wonder if anyone knows how cold it has to get before frost and ice will not freeze to things?

gary350 said:

Winter is here I have had frost on my vehicle windows every morning until we had -17 several weeks ago and -20 this morning there was no frost or ice on the window. Today when I saw no frost & no ice on window at -20 it reminded me of the microwave tower.

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What was the wind doing at those temperatures? Wind is a key player in when and how frost will form along with other things like relative humidity. Understand frost, freeze and dew point is a pretty good read on the subject. Most of it runs with what you mentioned. How cold can it get before frost won't form? I really don't know. A long time ago I did some work requiring dew point analysis and measuring dew point but our only concern was measuring dew point and our ambient air was never below 0 F. When living in Southern CA the orange groves did have towers with large engines driving large propellers which were run if frost was predicted. Cold air on clear, calm nights sinks to ground level. I assumed the props were to keep air moving and help prevent frost from destroying the oranges but never knew for sure? Cold air does not hold as much water vapor as warm air, so the vapor (or gas) turns to a liquid and forms dew. That process is called condensation. The condensate freezes and we have frost but I never gave much thought to how cold could the air be that it would hold no water? I know we can make dry air but as to what nature can do never gave it much thought.

Hope there are more thoughts to this.

Ron