Yaesu FT-897 Operating Manual

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Page 7FT-897 OPERATING MANUALI NSTALLATIONGROUNDINGThe provision of an effective ground system is important inany successful communications station. A good ground sys-tem can contribute to station efficiency in a number of ways: It can minimize the possibility of electrical shock to theoperator. It can minimize RF currents flowing on the shield of thecoaxial cable and the chassis of the transceiver whichmay cause interference to nearby home entertainmentdevices or laboratory test equipment. It can minimize the possibility of erratic transceiver op-eration caused by RF feedback or improper current flowthrough logic devices.An effective earth ground system may take several forms;for a more complete discussion, see an appropriate RF engi-neering text. The information presented below is intendedonly as a guideline.Inspect the ground system – inside the station as well asoutside – on a regular basis so as to ensure maximum per-formance and safety.Mobile Station GroundingAlthough satisfactory grounding in most installations willbe achieved via the DC cable’s negative lead and the an-tenna system’s coaxial cable shield, it is often recommendedthat you provide a direct ground connection to the vehiclechassis at the mounting location of the transceiver (installa-tion using the optional MMB-80 Mounting Bracket will ac-complish this, if the MMB-80 itself is mounted to thevehicle’s chassis). Due to unexpected resonance which maynaturally occur in any location, improper communicationsystem performance may result from insufficient ground-ing. These symptoms may include: RF feedback (resulting in distortion on your transmittedsignal); Unintended frequency change; Blinking or blanking of the frequency display; Noise pickup; and/orons may occur in any communica-tions installation. The FT-897 includes extensive filteringdesigned to minimize the chance of such problems; how-ever, random currents set up by insufficient RF groundingcan nullify such filtering. Bonding the rear panel Groundlug of the FT-897 transceiver to the vehicle or vessel’sground system should clear up any such difficulties.Vertex Standard does not recommend the use of “on glass”mobile antennas unless the shield of the coaxial cable is se-curely grounded near the feedpoint of the antenna. Suchantennas frequently are responsible for the ground-relateddifficulties described above.Base Station Earth GroundingTypically, the ground connection consists of one or morecopper-clad steel rods, driven into the ground. If multipleground rods are used, they should be configured in a “V”configuration, and bonded together at the apex of the “V”which is nearest the station location. Use a heavy, braidedcable (such as the discarded shield from type RG-213 co-axial cable) and strong cable clamps to secure the braidedcables to the ground rods. Be sure to weatherproof the con-nections to ensure many years of reliable service. Use thesame type of heavy, braided cable for the connections to thestation ground bus (described below).Do not use gas line pipes in an attempt to provide a groundconnection! To do so creates a serious risk of explosion!!Inside the station, a common ground bus consisting of a cop-per pipe of at least 25 mm (1”) diameter should be used. Analternative station ground bus may consist of a wide copperplate (single-sided circuit board material is ideal) securedto the bottom of the operating desk. Grounding connectionsfrom individual devices such as transceivers, power sup-plies, and data communications devices should be made di-rectly to the ground bus using a heavy, braided cable.Do not make ground connections from one electrical deviceto another, and thence to the ground bus. This so-called“Daisy Chain” grounding technique may nullify any attemptat effective radio frequency grounding. See the drawingsbelow for examples of proper and improper ground connec-tions. If your coaxial cable does not connect directly to thestation ground bus, you may connect a ground cable to theGround lug on the FT-897 rear panel.Proper Ground ConnectionLinearAmplifierPowerSupplyTransceiverImproper Ground ConnectionTransceiver LinearAmplifierPowerSupply"Daisy Chain"GND Terminal