The C-band Floppy Dish (not Disk) problem

Loose main support bolt and nut?

Sometimes we overlook the obvious. If you have a large C-band dish that seems difficult to aim, or that seems to lose signal strength during or after a strong wind, it could be that the main support bolt and nut are not tight enough. On certain types of mounts (probably most of them), if this bolt and nut are not tightened completely there can be a lot of “slop” in the dish, and it will especially give you fits when you’re trying to aim it at a satellite (especially one near the center of the arc) because of the way it flops around. Unfortunately, it may not be possible to get this bolt completely tight with a standard crescent or box wrench, unless you’re stronger than most. You may need a breaker bar and a socket to get it tight. An electric or air-driven impact wrench, such as the type an auto mechanic uses to tighten lug nuts, might also work, but I’d still suggest using a breaker bar for the final tightening.

On the dish pictured above, even though the nut and bolt seemed tight (at least when trying to tighten it with crescent wrenches), the use of a breaker bar allowed further tightening of more than the width of the nut! Of course you don’t want to apply so much torque that you break the bolt, but the U-shaped channel that holds the main support needs to be tight if you don’t want the dish flopping around in the wind.  With a 10 foot dish, unless your breaker bar has fairly long handle or the bolt has been significantly weakened by rust, you’re probably going to have a hard time breaking the bolt, assuming you’re not a weight-lifter or are otherwise stronger than the average person.  With a smaller dish, you’ll probably need to be more careful, since the bolt is probably also a lot smaller.  The goal is to compress the U-channel so it is tight against the box-shaped center support of the mount, not to deform the U-channel and center support or break the bolt.

WARNING! Breaking the bolt can be dangerous, since it could allow the dish to slide off the mount and damage the dish or adjacent property, and/or injure anyone standing nearby.  Be especially careful with heavy fiberglass dishes.  A heavy dish falling on someone could cause serious injury, or even death! Keep children and pets away from the dish while you tighten this bolt, just in case!  If the dish is on a hill or other non-level ground, consider chaining or roping the dish mount to the pole, in such a way that if the bolt breaks the dish cannot roll or slide down the hill.

And if the title of this article confuses you, you’re probably one of those darn kids that has never seen an older computer, or a rotary dial telephone or a pocket calculator for that matter.  This will enlighten you.

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