[BC] Re: Sat dishes vs snow

[Mike McCarthy]

A client here installed a 3.8 meter dish a few years ago.  3 phase 60A 
dedicated circuit for the dish heater.  And it's not a very high 
temperature system either.  Just enough to keep the snow off the dish as 
it's falling.  But not enough to keep runoff from freezing at it's 
perimeter and backing up water onto the dish for a foot or so.  It's a high 
angle dish.

MM

At 11:24 PM 1/4/2006 -0600, Sherrod Munday wrote
>On Wednesday 04 January 2006 22:01, WFIFeng at aol.com wrote:
> > Hmmm... cut a hole into this expensive cover, and stick a hose in? Using
> > one of the zippered slots for the feedhorn struts might work... I don't
> > know, though. Too fragile, and almost an invitation to local kids to
> > vandalize.
> >
> > I was thinking more along the lines of placing a small electric heater (the
> > forced-air ceramic type) inside the dish, and just run an extension cord to
> > the building. That is what I meant as being disruptive to the focus. I
> > don't think I want to try that, though.
>
>One of our affiliates did exactly this quite successfully a few years ago.
>The only disruption to the focus is the small (9" x 9" or so) footprint of
>the small heater.  That much of the dish's collector area (i.e. the area
>under the small heater itself) is not getting the signal back to the LNB --
>and that's trivial compared to the rest of the dish if you're using a 3.8m
>dish (which most of the CONUS downlink sites can quite successfully use for
>most of the commercial networks).  (For the math nerds out there, that would
>be 0.4% of the total aperature area of the dish, ignoring the LNB and mounts,
>etc.)
>
>Get a standard hardware or country supply store tarp (or Wally World for 
>those
>of you that are corporate America nuts ;-), stretch it across the dish
>aperature, and stick a little ceramic heater inside it.  Plug it into a
>thermostat-controlled outlet set for 35-40 degrees or so, and leave it alone.
>
>Sure, it may not make it to 80 degrees inside there, but if you can keep it
>above freezing by a few degrees it should help the snow/sleet/ice from
>building up on the tarp's surface.
>
>Another trick you might employ is to use some good old 3M Scotchgard fabric
>protector spray on a tarp.  The spray itself might not stick to straight
>plastic, so YMMV, but another place to look is a tent-type or camping supply
>to find a non-plastic tarp that will take the waterproofing spray better.
>Or, see if you can locate some spray-on Teflon for a tarp...
>
>Here's a link to liquid Teflon intended for carpet uses.  Perhaps a direct
>application to the dish might work, or application to a dish cover.
>http://www.baneclene.com/catalog/teflon.html
>
>Another deicing liquid intended for ground use, not fabric or metal:
>http://www.popularmechanics.com/home_improvement/home_improvement/1275751.html
>
>And finally, you could just go buy a dish ice shield/cover/tarp that already
>comes with a lubricant applied to make it more slick so that ice and snow
>cannot adhere as well.  They cost a bit but are commercially available.
>
>Check out the following links.  Beware the first option (at the very 
>bottom of
>the web page) could lead to some ultra-conservative communities banning it as
>being too risque or similar to half a bikini top...
>http://www.satellitedish.com/Page_13.htm
>http://www.sepatriot.com/snowcvr.htm
>
>And for a custom-spec'd cover:
>www.dawnsat.com/auto_links/pdf/CS3.51X4.1-15OZ.pdf
>
>I don't know if any of these solutions other than a surface treatment that
>would help a 60' dish (sorry, Dennis).  That would be a really *big* cover
>that would lead to its own support requirements...
>
>BTW, I know of one uplink site that uses heaters/deicers on their large 
>uplink
>dishes (e.g. ones that are 9m, 15m etc.).  They have to -- they are located
>in the Chicago area.  From what they mentioned, the electricity to run the
>deicers each season is not insignificant...  Essentially (IIRC) they had to
>run separate power trunks from their main feedlines to provide enough juice
>to heat up the dishes sufficiently.
>
>For the curious, they use rear-heating.  A cavity is formed behind the
>reflector surface with an essentially duplicate dish-shaped surface that is
>spaced away from the front reflector.  Then, hot air blowers pump air into
>and around that cavity continously when the system is on.  That system takes
>quite a lot of electricity to run to maintain the amount of hot air required
>to keep the front reflector surface warm enough when it's below freezing (or
>frankly, below zero in some cases).
>
>--
>Sherrod Munday <smunday at srnradio.com>
>Technical Director
>Salem Radio Network    (972) 831-1920
>
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