Yaesu FT-857D Operating Manual

Also see for FT-857 series: Manual Technical supplement Operation manual Brochure & specs Technical supplement

Contents

Yaesu FT-857D Operating Manual Manual pdf 14 page image

12 FT-857 Operating ManualANTENNA CONSIDERATIONSThe antenna systems connected to your FT-857 transceiver are, of course, critically impor-tant in ensuring successful communications. The FT-857 is designed for use with any an-tenna system providing a 50 W resistive impedance at the desired operating frequency. Whileminor excursions from the 50 W specification are of no consequence, the power amplifier’sprotection circuitry will begin to reduce the power output of there is more than a 50% diver-gence from the specified impedance (less than 33 W or greater than 75 W, corresponding toa Standing Wave Ratio (SWR) of 1.5:1).Two antenna jacks are provided on the rear panel of the FT-857. The “HF/50 MHz ANT”jack is used for HF and 50 MHz, while the “144/430 MHz ANT” jack is used for 144 MHzand 430 MHz.Guidelines for successful base and mobile station installations are shown below.Mobile Antenna InstallationsMobile antennas for the HF bands, with the possible exception of those designed for 28MHz, display very high “Q” due to the fact that they must be physically shortened, thenresonated using a loading coil. Additional system bandwidth may be realized using the YaesuFC-30 Automatic Antenna Tuner, which will present a 50 W impedance to your transceiveron the 1.8 ~ 50 MHz bands so long as the SWR on the coaxial line connected to the FC-30is below 3:1.On the VHF and UHF bands, coaxial line losses increase so rapidly in the presence of SWRthat we recommend that all impedance matching to 50 W be performed at the antennafeedpoint.Yaesu’s Active-Tuned Antenna System (ATAS-100/-120) is a unique HF/VHF/UHF mo-bile antenna system, which provides automatic tuning when used with the FT-857. See page68 for full details on the ATAS-100/-120.For VHF/UHF weak-signal (CW/SSB) operation, remember that the antenna polarizationstandard for these modes is horizontal, not vertical, so you must use a loop or otherwisehorizontally-polarized antenna so as to avoid cross-polarization loss of signal strength (whichcan be 20 dB or more!). On HF, signals propagated via the ionosphere develop mixed polar-izations, so antenna selection may be made strictly on mechanical considerations; verticalantennas are almost always utilized on HF for this reason.In mobile (and portable) installations, when vertical antennas are used, remember that thegrounding of the base area of the antenna is critically important to proper operation. Sincemost HF vertical antennas emulate a quarter-wavelength “monopole” antenna, the “missinghalf” of the dipole antenna consists of a counterpoise of radial ground system. In a vehicle,if mounting the antenna to a door or hatch, it is recommended that you bond the door to theINSTALLATION