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The head end amplifier cabinet is supplied with feed-through F connectors. The shipyard may wish to
change over from RG-11 cable to RG-6 with a pigtail splice near the cabinet; alternatively, RG-11 may
be connected direct to the F connectors on the cabinet if convenient.
All coaxial cables should be tagged on each end with a non-metallic tag. The tag ID should be
indicated on as-fitted drawings.
Outlets are supplied with plastic ground isolation bases. These reduce possible problems with ground
loops aboard a steel ship. When making connections to these “passives”, the connector may be
slightly wrench-torqued so as to insure a lasting connection throughout the life of the ship.
Water resistant F-connectors with Silicone gel sealant and O rings are available on request for RG-6
and RG-59 cables, but are not yet available for RG-11. A good quality connector should be selected
(such as Amphenol), as well as a quality crimping tool. It is important for the installer to be properly
skilled in making these connections. RG-11 is best for the branch runs from the head end to the first
passive connection; RG-6 can be used after that, providing the runs are not excessive in length. Keep
in mind that coax-cable losses affect the UHF frequencies much more than the lower VHF frequencies
so it is possible to lose the upper UHF channels altogether if the coax length and losses are
excessive.
Testing:
Equipment Required:
-TDR (Time Domain Reflectometer): Tektronics or equivalent.
- Frequency Selective Voltmeter: SENCOR or equivalent
Test procedures:
TDR reading should be taken on each piece of coaxial cable where physical measurements are not
possible. Lengths of all cables (to one foot accuracy) should be shown on as-fitted drawings. In
addition to determining cable lengths, the TDR is able to see anomalies on the coax, and the installer
should use this feature to insure that the cables and connections are true.
Perform a system test after installation is completed, before closing ceiling panels, etc. Inject a pilot
signal at the head end. For this purpose, a VCR generates a good signal and is convenient to use as
a pilot signal generator, as it is a repeatable signal source for future troubleshooting.
Experiences have shown that Shore Cable signals can vary from hour to hour and as such should not
be used to inventory system levels. Most VCR units usually have a switch to allow RF output on either
channel 2 or 3. Use either channel for the test; note the channel chosen on the as-fitted drawings.
When used with PRA-422/PRA-420 Power Supply-Amplifier, Attenuators: Each attenuator is a 3 turn
potentiometer and is rather delicate. Use a tuning tool or small screwdriver. Turn slowly so the end of
travel stop may be felt..
Inject the VCR signal to the selected input port on the PRA-422/PR-420. While viewing the
appropriate channel on the TV monitor, reduce attenuation on the amplifier until some signal
degradation is noticed; then increase attenuation until this degradation is reduced. The amplifier is
now adjusted for maximum gain without overdriving it. (The attenuator is situated at the amplifier
input) Note the level of this Pilot. This level should be recorded and will be the reference point for all
further tests.
