2.4 DSS and RAIN !!!!!!!!!!!

Nice quadruple spacing there. Dramatic pause?

2.4GHz == Microwaves. Water good at absorbing microwaves. The up side, is you can stick your antenna in your coffee and heat it back up ;) LOL

Jim

Thanks Doc. There's nothing better then first hand info. mk

Yup. 2.4GHz is the peak absorption part of the H20 spectrum.

Bugger innit?

| Yup. 2.4GHz is the peak absorption part of the H20 spectrum.

Absolutely not, but it is certainly a common misconception.

In fact, 2.4 GHz signals are only attentuated by about 0.05 dB/km in a heavy downpour. The same rainfall would attenuate a 5.8 GHz singals by about 0.5 dB/km -- ten times as much. 12 GHz (like used by Dish Network) is attenuated even more than that.

Rain fade figures come from

and here's a nice graph --

Looks like the peak is really about 200 GHz.

2.4 GHz is sort of a compromise -- the signal can penetrate several inches of water (like in a glass of water -- I'm not talking about rain), but is still absorbed by it somewhat. It's this that allows your food to be cooked somewhat evenly by your microwave oven -- if the frequency were a lot higher, only the outer layer of your food would get hot.

2.4 GHz microwaves are much larger than rain drops, so they are barely affected by rain drops. As the wavelength gets smaller, the raindrops have a larger and larger effect.

Though rain fade has been well studied by microwave engineers for decades now -- but what they've found really doesn't explain why people flying 2.4 GHz R/C gear have reported greatly reduced range in the rain at all.

suggests that rain fade is signifigant even at 2.4 GHz -- but only for really long links -- dozens of miles, rather than a fraction of one, and only with really heavy rain.

when some people I knew were setting up 2.4GHz wifi links, they found that wet leaves were terrible, and rain and fog really attenuated a LOT more than you are saying. I mean like 20-30dB over a few hundred meters.

The Natural Philosopher wrote in news:1180648053.20977.0 @iris.uk.clara.net:

Which leads us to suspect that the problem isn't rain fade, but perhaps multipathing or some other effect.

Or maybe that rain isn't pure water and has particulates that may interfere with signals. The amount of interference might vary from location to location depending on the amount of pollution being taken out of the air by the rain.

Maybe they are just not so simple minded... if you're flying your huge scale glider in the mountains, weather can change way faster than you can come in to land.

ED! You not a real man until you've stood in the middle of an open field with a lightening rod(72Mhz ant) making your plane disappear into the low clouds and spinning it down with rain hitting you in the face! Granted, with attitude(read stupidity) permeating my life, I may not live as long as you, but I may be remembered on the internet in the Darwin Awards. :) mk

On Fri, 1 Jun 2007 10:26:58 -0500, "MJKolodziej" wrote in :

One of the saddest days of my RC life was in a light rain.

I was suffering from flyitis.

I kept my TX upright on the ground and used a shopping bag over it while flying (ran the antenna through the bottom of the bag).

Another fellow saw me having fun in the rain and decided to fly, too. He had trouble starting the engine. I helped him get it going.

He lost radio control and crashed on his second circuit. He hadn't noticed what I was doing to keep the rain out of the TX case and I didn't notice his carelessness.

He dropped out of the club that summer and got into model trains. :o(

Marty

Open field? Naw, standing on top of a mountain flying your sloper into the evil dark underbelly of the storm with a half dozen other flier/lightning rods standing in a tight, "Come and get me!" formation. In a less instant death and more semi-swift death by erosion, standing on top of that same mountain in a 60 mph Santa Ana wind that is stripping all the loose crap off the fire bared hillsides up wind of you and scouring off your skin is a hoot also!

The only trouble you have with flying in the rain is if water runs down the transmitter antenna! Years ago I would tie a rag around the base of the antenna and flew in the rain all the time!

Now we're talking! mk

ROFLOL!

Ed, he is more right than wrong!

Some friends and I frequent an annual event in west Texas. I have been there something like 24 of the last 25 years.

A couple of years ago, the event started Saturday and it was raining steadily and fairly strongly. Since this event is that club's only revenue generator, my friends and I felt obligated to stay and see the weather out. After about 30 minutes of the rain, we got bored and broke the planes out and did touch and goes in the pouring rain by keeping the transmitters under raincoats. The club got the message and put up one of those easy ups and we all flew from under that all day. Others got the message and joined us..

They got over 2 inches of rain that day.

The event was a success and the planes were easy to clean that evening.

What a hoot!

I am not real sure I wish to give up that capability.

Now as to the original posters report. It is practical user reports of weaknesses that I desire before I convert several hundreds of dollars worth of electronics to the trash bin. I suspect the multipath issue is where the weakness may be, but time will tell.

Jim Branaum AMA 1428

Mark Miller a écrit :

Now you know why the microwave ovens use 2.4GHz. It is readily absorbed by water. A few drops have very little effect... but when it's pourring. Ok?