Antenna Considerations; About Coaxial Cable - Yaesu FT-991 Operating Manual

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The FT-991 is designed for use with any antenna system providing a 50 Ohm resistive impedance at the desired oper-
ating frequency. While minor excursions from the 50-Ohm specification are of no consequence, if the Standing Wave
Ratio (SWR) present at the Antenna jack is greater than 3:1, the transceiver's Automatic Antenna Tuner may not be able
to reduce the impedance mismatch to an acceptable value.
Every effort should be made to ensure that the impedance of the antenna system be as close as possible to the specified
50-Ohm value. Note that the "G5RV" type antenna does not provide a 50-Ohm impedance on all HF Amateur bands. An
external wide-range antenna coupler must be used with this antenna type.
Any antenna to be used with the FT-991 must be fed from the transceiver with 50 Ohm coaxial cable. Therefore, when
using a "balanced" antenna such as a dipole, remember that a balun or other matching/balancing device must be used to
ensure proper antenna performance.
The same precautions apply to any additional (receive-only) antennas connected to the antenna jacks. If the receive only
antennas do not have impedance near 50 Ohms at the operating frequency, It may be necessary to install an external an-
tenna tuner to obtain optimum performance.
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Use high-quality 50-Ohm coaxial cable for the lead-in to your FT-991 transceiver. All efforts at providing an efficient
antenna system will be wasted if poor quality, lossy coaxial cable is used. This transceiver utilizes standard "M" ("PL-
259") type connectors.
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F T-991 O M Page 11
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