Yaesu FT-897 Operating Manual

Also see for FT-897: Manual Brochure & specs Operating manual Technical supplement Service manual

Yaesu FT-897 Operating Manual Manual pdf 10 page image

Page 8 FT-897 OPERATING MANUALANTENNA C ONSIDERATIONSThe antenna systems connected to your FT-897 transceiverare, of course, critically important in ensuring successfulcommunications. The FT-897 is designed for use with anyantenna system providing a 50 Ω resistive impedance at thedesired operating frequency. While minor excursions fromthe 50 Ω specification are of no consequence, the poweramplifier’s protection circuitry will begin to reduce the poweroutput of there is more than a 50% divergence from the speci-fied impedance (less than 33 Ω or greater than 75 Ω, corre-sponding to a Standing Wave Ratio (SWR) of 1.5:1).Two antenna jacks are provided on the rear panel of the FT-897. The “HF/50 MHz ANT” jack is used for HF and 50MHz, while the “144/430 MHz ANT” jack is used for 144MHz and 430 MHz.Guidelines for successful base and mobile station installa-tions are shown below.Mobile Antenna InstallationsMobile antennas for the HF bands, with the possible excep-tion of those designed for 28 MHz, display very high “Q”due to the fact that they must be physically shortened, thenresonated using a loading coil. Additional system bandwidthmay be realized using the Yaesu FC-30 Automatic AntennaTuner, which will present a 50 Ω impedance to your trans-ceiver on the 1.8 ~ 50 MHz bands so long as the SWR onthe coaxial line connected to the FC-30 is below 3:1.On the VHF and UHF bands, coaxial line losses increase sorapidly in the presence of SWR that we recommend that allimpedance matching to 50 Ω be performed at the antennafeedpoint.Yaesu’s Active-Tuned Antenna System (ATAS-100/-120)is a unique HF/VHF/UHF mobile antenna system, whichprovides automatic tuning when used with the FT-897. Seepage 39 for full details on the ATAS-100/-120.For VHF/UHF weak-signal (CW/SSB) operation, remem-ber that the antenna polarization standard for these modes ishorizontal, not vertical, so you must use a loop or otherwisehorizontally-polarized antenna so as to avoid cross-polar-ization loss of signal strength (which can be 20 dB or more!).On HF, signals propagated via the ionosphere develop mixedpolarizations, so antenna selection may be made strictly onmechanical considerations; vertical antennas are almost al-ways utilized on HF for this reason.Base Station Antenna InstallationsWhen installing a “balanced” antenna such as a Yagi or di-pole, remember that the FT-897 is designed for use with an(unbalanced) coaxial feedline. Always use a balun or otherbalancing device so as to ensure proper antenna system per-formance.Use high-quality 50 Ω coaxial cable for the lead-in to yourFT-897 transceiver. All efforts at providing an efficient an-tenna system will be wasted if poor quality, lossy coaxialcable is used. Losses in coaxial lines increase as the fre-quency increases, so a coaxial line with 0.5 dB of loss at 7MHz may have 6 dB of loss at 432 MHz (thereby consum-ing 75% of your transceiver’s power output!). As a generalrule, smaller-diameter coaxial cables tend to have higherlosses than larger-diameter cables, although the precise dif-ferences depend on the cable construction, materials, andthe quality of the connectors used with the cable. See thecable manufacturers’ specifications for details.For reference, the chart below shows approximate loss fig-ures for typically- available coaxial cables frequently usedin HF installations.Loss in dB per 30 m (100 feet)for Selected 50-ohm Coaxial CablesLossCable Type 1.8 MHz 28 MHz 432 MHzRG-58A 0.55 2.60 >10RG-58 Form 0.54 2.00 8.0RG-8X 0.39 1.85 7.0RG-8A, RG-213 0.27 1.25 5.9RG-8 Form 0.22 0.88 3.7Belden 9913 0.18 0.69 2.97/8” “Hardline” <0.1 0.25 1.3Loss figures are approximate; consult cable manufacturer’scatalogs for complete specifications.Always locate antennas such that they can never come incontact with outdoor power lines in the event of a catastrophicsupport or power-pole structural failure. Ground your an-tennas’ support structure(s) adequately, so as to dissipateenergy absorbed during a lightning strike. Install appropri-ate lightning arrestors in the antenna coaxial cables (androtator cables, if rotary antennas are used).In the event of an approaching electrical storm, disconnectall antenna lead-in, rotator cables, and power cables com-pletely from your station if the storm is not immediatelyin your area. Do not allow disconnected cables to touch thecase of your FT-897 transceiver or accessories, as lightningcan easily jump from the cable to the circuitry of your trans-ceiver via the case, causing irreparable damage. If a light-ning storm is in progress in your immediate area, do notattempt to disconnect the cables, as you could be killed in-stantly if lightning should strike your antenna structure or anearby power line.If a vertical antenna is utilized, be certain that humans and/or pets and farm animals are kept away both from the radiat-ing element (to prevent electrical shock and RF exposuredanger) and the ground system (in the event of an electricalstorm). The buried radials of a ground-mounted verticalantenna can carry lethal voltages outward from the center ofthe antenna in the event of a direct lightning strike.I NSTALLATION