Yaesu FT-847 Operating Manual

Also see for FT-847: Technical supplement Technical supplement Technical supplement Modification

Contents

10 FT-847 OPERATING MANUALANTENNA CONSIDERATIONSInstallationThe antenna systems connected to your FT-847 trans-ceiver are, of course, critically important in ensuringsuccessful communications. The FT-847 is designedfor use with any antenna system providing a 50Ω re-sistive impedance at the desired operating frequency.While minor excursions from the 50Ω specificationare of no consequence, the power amplifier’s protec-tion circuitry will begin to reduce the power output ofthere is more than a 50% divergence from the speci-fied impedance (less than 33Ω or greater than 75Ω,corresponding to a Standing Wave Ratio (SWR) of1.5:1).Four antenna jacks are provided on the rear panel ofthe FT-847, using two different types of connectors.Three of these jacks are “Type M” (SO-239) jacks;these are the HF, 50 MHz, and 144 MHz jacks. Theother jack is a “Type N” jack, which is the 430 MHzjack.The center pins of these two jack types are of verydifferent diameters, and damage (not covered by yourtransceiver’s Limited Warranty) will be caused if youattempt to connect a Type M (PL-259) plug to the 430MHz Type N jack. It is best to confirm visually thatyou are connecting your coaxial cables to the correctjacks.Guidelines for successful base and mobile station in-stallations are shown below.Base Station AntennaInstallationsWhen installing a “balanced” antenna such as a Yagior dipole, remember that the FT-847 is designed foruse with an (unbalanced) coaxial feedline. Alwaysuse a balun or other balancing device so as to ensureproper antenna system performance.Use high-quality 50Ω coaxial cable for the lead-in toyour FT-847 transceiver. All efforts at providing anefficient antenna system will be wasted if poor qual-ity, lossy coaxial cable is used. Losses in coaxial linesincrease as the frequency increases, so a coaxial linewith 0.5 dB of loss at 7 MHz may have 6 dB of loss at432 MHz (thereby consuming 75% of yourtransceiver’s power output!). As a general rule, smaller-diameter coaxial cables tend to have higher losses thanlarger-diameter cables, although the precise differencesdepend on the cable construction, materials, and thequality of the connectors used with the cable. See thecable manufacturers’ specifications for details.For reference, the chart below shows approximate lossfigures for typically-available coaxial cables frequentlyused in HF installations.CABLE TYPE LOSS1.8 MHz 28 MHz 432 MHzRG-58A 0.55 2.60 >10RG-58 Foam 0.54 2.00 8.0RG-8X 0.39 1.85 7.0RG-8A, RG-213 0.27 1.25 5.9RG-8 Foam 0.22 0.88 3.7Belden 9913 0.18 0.69 2.97/8" "Hardline" <0.1 0.25 1.3Loss in dB per 30m (100 feet)for Selected 50Ω Coaxial Cables(Assumes 50Ω Input/Output Terminations)Loss figures are approximate;consult cable manufacturers'catalogs for complete specifica-tions.