MFJ-1778 G5RV 10-160 m, 31 m long, > 11 m high, 1500 W
The G5RV antenna is a multi-band center-fed dipole antenna capable of 1500 Watts. It was originally designed to operate as a 3/2 wavelength center fed antenna for 14 MHz, but amateurs soon discovered it would offer reasonable performance on many other bands.
The MFJ-1778 (G5RV) consists of a 102 foot flat top fed with a 32.5 foot 450 ohm matching section ending in an SO-239 coaxial connector. The 450 ohm balanced transmission line serves as a 1:1 transmission line transformer on 14 MHz. The SWR is approximately 2:1 at 14 MHz. The same balanced line section acts like a transmission line impedance matching section on the other HF bands. This antenna generally requires the use of a suitable matching network (antenna tuner) since the SWR of the G5RV is almost certainly not 1:1 on any band. The use of a tuner will guarantee maximum performance from solid state exciters.
The G5RV is a balanced antenna that is fed by an unbalanced coaxial line. This feed system causes
unwanted parallel RF currents to appear on the shield of the coaxial feedline. A choke type balun
should be used with this antenna to eliminate or reduce the undesirable parallel feedline currents.
Failure to use a choke balun may result in RFI, RF feedback, or other symptoms of RF "in the shack". The Manual describes how to construct a basic choke balun for this antenna. Or even better buy a separate professional choke balun like Balun Designs 1115du (se under section “Baluns”).