The year is flying by, and
even though you may still be in end-of-summer mode, many areas of the
country will be experiencing snow sooner than you realize (or want to
think about). Snow and ice are a pain for anyone, but especially if
you maintain satellite dishes. So take advantage of the crisper fall
weather and wax the surface of your satellite dish to make snow
Fig. 1: Here is Aaron Read’s homebrew dish heater.
My preferred choice is
marine wax. If your dish has a cover, however, application of a
waterproofing compound is a good call, too. A popular waterproofing
spray for camping is Kiwi Heavy Duty Water Repellant. You’ll find
this product at most sporting goods stores, or find a link to
information at radioworld.com/links.
The waterproofing compound
helps guard against the cover freezing. After applying this or wax,
it’s time for some instruction. Your on-air staff needs to know how
to remove the snow properly, sweeping it out and not deforming the
dish in the process. In the case of the dish cover, making sure no
one tears the fabric.
Explain that the satellite
signal will be lost if they bang under the dish to get the snow out.
Rough treatment is not needed, especially when you have waxed the
dish so the snow comes off easily. A long-handled squeegee works
well, and the rubber edge will help minimize any damage to the dish
as it is swept through the parabola. Periodic sweeping of the snow
eliminates a large amount of snow from forming, in which case the
weight can deform the dish.
* * *
Aaron Read handles
technical matters for Rhode Island
Public Radio, an NPR affiliate. They have the standard 3.8m C-band
downlink, used for reception of public radio programming. However,
limitations at his
studios, they had to locate the dish at their North Providence
transmitter site, about 3 miles away.
has been problematic during the frequent snowstorms in Providence, as
it doesn’t take much ice
or wet snow to block the signal, even with a dish cover. Typically stations have a staff member
on-call to physically sweep the snow off the
dish cover, but that’s not practical for Aaron’s station, since
the dish is located at a remote site.
the dish is only 10 feet from a two-story transmitter building, with a large, forced-air
furnace to heat the building. Aaron cooked up a system to route the
heated air from the furnace out to the dish, circulate it in the
space between the dish cover and the dish itself, and return the air
back to the building in a “closed loop” to increase efficiency
and decrease dirt from being sucked into the building.
idea is that the heat inside the space will melt any snow or ice
attached to the cover, and wax on the cover lets it slide right off.
took a lot of experimentation and more heat than Aaron had anticipated. Originally he had
hoped that ambient air, drawn from near
a ceiling heat vent, would be sufficient to melt the snow, but
wasn’t even close.
Aaron ran a six-inch-diameter, heavily insulated dryer vent hose; and
connected it directly to the main hot air vent output of the furnace,
raising the air vents to 130 degrees Fahrenheit and providing a much
higher CFM — roughly 800 — out to the dish. (CFM stands for cubic
feet per minute, a term used to measure airflow.)
run is 50 feet to the dish (with an in-vent 300 CFM vent fan halfway
through at the building
wall), and through a reinforced hole in the dish cover. On the
opposite side of the cover is another reinforced hole with a 25-foot
insulated vent tube, six inches in diameter, and another vent fan
sucking air back into the
interior of the building.
project was a major tradeoff in cost vs. expectations. Aaron could have spent $10,000 to $16,000
for a proper dish heater system, which would have a set level of
expectations from the get-go. Instead, he spent
less than $2,000 (and $500 of that was for a contractor to bore two
holes into the building’s
exterior wall, which was made of concrete blocks). The only downside
to this operation was that it took several
weeks of trying new configurations — and waiting for snowstorms —
to test each configuration.
only major change would be to center the inflow vent on the dish
cover at the bottom, and place the return at the top. The dish is
mounted on the side of a hill, and it was logistically impossible to
the end, though, it was sufficient to maintain service even during
“Snowmageddon” in February this year, when whiteout conditions
and snowfall rates exceeded two inches per hour. In other words, the
project was a success.
finished product can be seen in Fig. 1.
a good time to inspect the outside of your site before winter
arrives. Even if you aren’t using a dish, you never know when
programming will want it pressed into service. So, things like the
open feed in Fig. 2 should be corrected. Terminate the coax so that
the connector can be reused, and waterproof the connector, even if
it’s with electrical tape. At the very least, affix a heavy plastic
bag over the feed horn assembly to keep it dry.
to Workbench. You’ll help your fellow engineers, and qualify for
SBE recertification credit. Send Workbench tips to
Fax to (603) 472-4944.
John Bisset has spent 44 years in the broadcasting industry and is
still learning. He handles West Coast sales for the Telos Alliance.
He is SBE Certified and is a past recipient of the SBE’s Educator
of the Year Award.