Ok, that makes sense...Wondering how I could incorporate a zig-zag if I were to try this for a temporary solution....Inside of the top cone would need to be solid, but perhaps on the outside, I could cut out a zig-zag design....Or maybe cut out strips of foil to spiral around the outside leaving gaps in between.

Would crinkling the foil also serve the same purpose of increasing resistance?

NO!! Crinkling will have no effect on the current path, no change in resistance.
and there is an issue with aluminum, foil or otherwise, which is that it does have a tendency to corrode , especially in the presence of moisture and electrical currents.

The suggestion of using the ceramic tube style higher wattage wire-wound resistors, mentioned in post #18 is quite good, in that you could easily have a predicted wattage (power) heater that would avoid any reliability issues. And it could be small enough to fit inside the rain gage housing. And if the connections were soldered it will probably last for many years. The big challenge will be deciding how many watts of heat to provide. My suggestion is "not very much", you do not want to melt anything.. Probably some others can offer a more detailed suggestion.

 

Wxman,

Ya’akov and others have given a comprehensive set of very good suggestions. I’ll add one idea about making the heating element itself, based on a similar gadget I built about 40 years ago.

You can make a simple low-wattage heating element by using 1/4 or 1/2 watt carbon resistors wired in series and-or parallel. For example, a 2.7K or 3.3K resistor with 12 VDC across it will provide about 50 milliwatts of heat. You could glue an array of them to the outside surface of the funnel. As I recall, I used about 80 or 90 resistors, all wired in parallel, glued to the outside surface with RTV. This will allow you to adapt to the size and shape of the funnel. It’s a simple piecewise way to make a custom heating “blanket” that conforms to the surface you need to keep warm. Just pick the resistor value and number of them to achieve the heating you want, add up the total current, and pick a power supply.

 

Have you considered using heat tape, the stuff used to keep pipes from freezing? I think it uses a PTC material that automatically heats more when it gets cold (assuming a constant voltage supply). You can find the 110V type at places like Lowe's and Home Depot, and other voltages online (I just got some 12V powered stuff). My guess is that you could wrap the outside with heat tape and it would keep the inside warm enough to not freeze, at least in your climate.

 

The resistor scheme fromM27, in post #22 is by far the best so far.The benefit is that it can be an exact fir and an appropriate wattage actually bonded to the items needing heat applied. And it can be designed to work at whatever voltage you chose, with only the math being the hard part.

 

What many have used in the past is a light bulb. So if there is room for an E17 socket and bulb and 120Vac is available, the heat generated by the bulb will eventually melt the snow and or ice.