
SG-2000 MANUAL
86
The SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA
©1995, SGC, Inc.
TEL: (206) 746-6310 FAX: (206) 746-6384
14.0 Mobile Installation
Many tips regarding mobile installation have been given in the preceding
chapters, but such a large and important field warrants its own chapter.
14.1
Shock and Vibration Mounting
The need for shock mounting is widely misunderstood in radio circles. There are
two issues with regard to shock mounting which must be considered: physical
displacement and frequency.
Displacement is how far a unit moves when vibration occurs. In a vehicle, this
may be a small fraction of an inch. The displacement on a sailboat can be 20 feet
— if the vessel is operating in 20-foot seas.
Frequency is how often a change of direction takes place. On a vehicle,
frequencies may run up to many times per second, while on a sailboat the
frequency may be one cycle in 2 minutes. A high speed paramilitary RIB (Rigid
Inflatable Boat) might encounter shocks at 1 per second, or greater rates
depending on sea state and mission. This requires shock mounting.
To estimate whether a shock mounting is required in a particular installation,
multiply the frequency (in cycles per second) times the displacement (in inches).
If the resulting number is greater than three, a shock mounting tray should be
considered. With a value over five, a shock mounting is mandatory.
Let's look at the sailboat numbers:
In a 10 foot sea, with a wave period of 1 minute, the calculation is:
120" times 1/60th of a cycle per second = a vibration factor of 2.
So in this case, installation of a shock mount is not necessary.
But let's look at what happens on a military four wheel drive vehicle racing
across the back country at 60 miles per hour. Here, the displacement can be 3
inches and the frequency up to 2 times per second. In this case, the calculation
would be:
3 inches times 2 = a vibration factor of 6.
A shock mount is obviously needed. But let's consider a family vehicle driven on
average city streets and highways. Here, displacement would be 1/2 inch or
less. This means a calculation of:
.5 inch times 2 = a vibration factor of 1.