From: rxv9839@ritvax.isc.rit.edu (Bob Vogel)
Newsgroups: rec.video.satellite
Subject: Re: Snow in the dish
Date: 30 Dec 92 01:19:57 GMT
Reply-To: rxv9839@ritvax.isc.rit.edu
Organization: Rochester Institute of Technology

In article <1992Dec29.043333.11500@freenet.carleton.ca>, aa422@Freenet.
carleton.ca (Rene Kahle) writes:
>
>In a previous article, "Darwin L. Mecham W-7211 BD9A/752" () says:
>
>>I recently read a posting that indicated that snow weight would make
>>tracking unreliable.
>
>I don't know.  One "satellite expert" told me to keep the dish parked
>pointed as horizontal as possible (in our case, Satcom C1) when not in use
>so the snow doesn't collect in the dish.  Another one told me to keep it
>pointed as vertical as possible (Spacenet 2) so the wind doesn't catch it.
>
>Well, I tend to believe the snow argument more, so I leave it pointed at
>C4 (on Deutsche Welle) when I know there's snow coming, and if any
>collects in it, I simply sweep it off to keep the picture clear and make
>sure that no problems develop with the rotor.
>
>I have more problems with wet leaves collecting in the dish in Fall than
>snow collecting in the dish in Winter.
>
>Happy New Year!
>
>-- 
>|  Rene Kahle         |  aa422@freenet.carleton.ca  |
>|    Kanata, Ontario  |                             |
>|    Canada           |  1:163/404.0@fidonet.org    |

Sorry to recap all that above, but my editor doesn't work just right for
deleting.
A few thoughts on snow in dishes--
Many, most, at least some commercial dishes in high snow/ice areas have
de-icers.  The most common is basically a big heater, usually gas fired or
electric, and a blower that blows the heat into a housing around the back of
the dish.  The most efficient ones re-use the air, thus re-suing some residual
heat.  They are EXPENSIVE because they are typically almost custom made. 
Another approach used is basically heat tape, either after add or some molded
in the dish.  It is just like the freeze tape that is wrapped around water
pipes in cold climates.  Most are just a big heater tape with a thermostat or
switch somewhere on it to turn it on and off.  Raychem makes some neat tape
that is the thermostat in itself, it doesn't conduct or heat until the
temperature drops to about 33 or 34 deg F.  The heat tape approach is fairly
cheap and should work especially well on metal dishes because of the good heat
conduction.  Its slow on fiberglass, the thicker the glass, the slower it
works.
The reason for the problem is two-fold {I'm open to theory correction or
improvement here}.
1.  Attenuation-Anything in the dish between the dish surface and the LNB
attenuates some of the signal.  From other posts it sounds like most home
dishes really begin to notice it after a few inches in the dish.  This will be
a gradual degradation and is simple to fix.  Brush, beat or whatever the snow
out of the dish.
All the methods recently posted {wax, rain-X, teflon coating} should be a help
in getting the snow to slide off in the first place.
2.  Dish shape change-When the snow is ice, when it melts and then freezes,
whatever happens that causes ice is a whole different matter.  Ice reflects
microwaves well.  Enough of it in a dish and its the dish.  A few inches of
change means usually very reduced signal to no signal until the ice is gone. 
This is why de-icers are used and why some very wet sonw can cause the same
situation, when it freezes into ice sheets on top.
Another idea for the pool-mesh dishes only-install a big fan behind the dish. 
Turn it on when its snowing and blow the snow out.
Bob Vogel