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Home > Forums > Electrical / Electronic Engineers > Activities > Antenna & Propagation engineering Forum

Dipole and Snow(2)

Read More Threads Like This One

RodgerB (Electrical)

6 Feb 08 10:58

I am looking for some input? Using a half wave dipole at 72 megahertz FM with the antenna mounted on a flat roof and with the base of the antenna sitting in 4-6 inches of snow. Will the impedance or SWR change due to the snow?
Thanks in advance
rodger.booth@verizon.net

biff44 (Electrical)

6 Feb 08 13:00

Snow is mostly air, and is not a problem. Ice is pure water which will load down the end of an antenna--mistuning it.

Higgler (Electrical)

6 Feb 08 17:02

If the antenna gets within 30 inches or so of the flat roof, the metal in the roof (if any) will start to degrade the antenna VSWR. 41" is 1/4 wavelength and below that length you can really see VSWR change.

biff44 is right, snow is air, ice is 3.2 dielectric and not too lossy, water is 81 dielectric and very lossy.

kch

biff44 (Electrical)

22 Feb 08 7:56

I did not realize that ice was only a 3.2! That is not so bad!

Higgler (Electrical)

22 Feb 08 11:44

Yup, 3.2.
Not sure of the loss tangent.
When it starts to melt is a problem.
I wonder how Direct TV does in the cold climates.

copy&pasted;
There is a high dielectric constant for ice at high frequencies (the constant is about 3.2). Ice has a very high dielectric relaxation time compared to water, and at higher frequencies the molecules are not able to
realign themselves to the changing electric field. This is why ice does not melt in a microwave as quickly as water comes to a boil.

kch

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