Ice / Radio Question

Andrew Geil

EF3
Joined
Mar 5, 2004
Messages
260
Location
Des Moines, Iowa
I have an odd question. And since a lot of you here are ham radio nutz, and like weather, your knowledge of the two should prove to be useful! :)

Recently, a good portion of the conuntry got iced in. Does ice accumulation on antennas affect radio transmission? I ask because my work (which uses UHF frequencies) was recently told our repeater (which we... *ick* rent) is having problems recieving/transmitting because of ice on the antenna. Is this a plasuable explanation?
 
This is a topic of debate among amatuers, more so as to how badly it affects the SWR of the different types of antennas. The truth is, yes it will affect the performance of antennas.

My 20meter dipole had about an 1/8th of an inch of ice on it up until today, and it was registering at 3.0 to 1 SWR from its previous reading of 1:1. I'm not sure about my VHF/UHF discone antenna that I use primarily for two meters since I don't have it hooked to any sort of meter, but it still functioned at low power levels into our local repeater.

Many antennas are affected by rain and snow as well, but usually not to the same degree. I like to have an indoor antenna of some sort for VHF/UHF use as a backup for these situations as well as lightning, and I'd imagine EMD's should have some sort of backup as well :wink:

Tim
 
Yes, ice on antennas will affect the signal going out. The ice will reflect part of the signal back in to the antenna, and thus the reflected signal acts against the outgoing signal. The end result is a weaker transmitted signal and power being fed back into the final satges of the transmitter circuit. Most modern transmitters will detect this feedback and cut back the power output to protect the circuit from overheating.
 
One of the principal reasons that ice affects SWR is conductivity. While pure water is not a good conductor, precipitation is an electrolyte due to the impuities from the atmosphere.

When ice clings to an antenna, it will change the electrical length of the antenna, knocking it out of tune. Also, a uniform coating of ice on an antenna will short circuit a path between the hot and ground poles.

The net effect of either situation is an elevated SWR. Antennas with exposed conductors, like a dipole, will me more susceptible to this than one thais pretty much sealed, like a commercially made dual band vertical.
 
It is well known on the summit of Mount Washington that ice has very little effect on radio antennas. Otherwise we would be very worried about the 6-20 feet that accumulates on the very powerful radio antennas that dot the summit. The consequences would not only be poor signal strength, but dangerous power consumption issues.

With that said, major problems begin to occur when ice and water are present. There was very poor reception yesterday during the big melt when it hit 43 (daily record) and all the ice was falling off.
 
The Mt Washington issue is a perfect example of the conductivity of precipitated water. The federal agancies that maintain communications atop the summit do not skimp on their antennas. They are well sealed, therefore, no issues with ice.

I'm willing to bet that melt water is an issue because the feedline connections are not well sealed. Water in the feedline significantly alters the impedance of the line, wreaking all kinds of havoc. It's funny, people will spend all kinds of money for a well made antenna, and then skimp on the quality of the feedline, and either poorly seal the connections or not seal them at all.
 
The Mt Washington issue is a perfect example of the conductivity of precipitated water. The federal agancies that maintain communications atop the summit do not skimp on their antennas. They are well sealed, therefore, no issues with ice.

I'm willing to bet that melt water is an issue because the feedline connections are not well sealed. Water in the feedline significantly alters the impedance of the line, wreaking all kinds of havoc. It's funny, people will spend all kinds of money for a well made antenna, and then skimp on the quality of the feedline, and either poorly seal the connections or not seal them at all.
Click to expand...

I think you got it exactly right. I wasn't sure about the details, but the problem is with leaks...all different kinds of leaks.
 
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