[BC] Comtech versus Patriot dishes

[Grady Moates]

> Thanks to all who replied.  Since I asked the question, I've
> been advised by Chris Krieger at RF Specialties that Comtech
> appears to be out of the 3.8 meter dish business.  He says
> that the closest he can come is a Prodelin dish. How about
> comments on them?

    WUMB had a Prodelin 8-petal, 3.4 meter az-el dish installed
in the early 2000s.  It lasted about 5 years on the flat roof
of the UMass Boston library building, on a Baird non-penetrating
roof mount.

    The petals are attached to each other with bolts through
holes in the fiberglass flanges along the edges of the petals.
The hardware supplied is only standard flat-washers, and the
surface area compressed by these washers is very small.
The force of the wind gusts over five years fatigued the
fiberglass so much that the bolts pulled through, and the
dish came apart in 70 mph wind gusts.  While the dish is rated
to survive higher winds, those ratings are apparently based
upon single-events, rather than repetitive, day-after-day
wind exposure.

    Unfortunately, our research indicated that, for our roof-
mounted location, no other dish was going to be both robust
and cost-effective.  We ended up buying an identical dish and
fabricating our own hardware for attaching the petals together,
using flat plates of 1/4" aluminum about 1.5" square, chamfered
along one edge, so that a much larger area of the flanges is
clamped, spreading the flex-forces across more fiberglass
material.  We also installed a snow-cover to help hold the front
of the reflector together.  We now wait 5 years to see if this
is an improvement.  SFSG.

Grady Moates, Director of Engineering
WUMB-FM Public Radio Network
University of Massachusetts Boston