G5RV MULTI-BAND

The G5RV multiband hf antenna..
A multiband antenna with open-wire ladder line into an antenna-tuner, has become popular as a simple all-band antenna, that does not require a lot of space, simple to construct and is low in cost.
The 31.2m (102ft) long G5RV, centre-fed antenna capable of very efficient operation on all hf bands from 3.5 to 28 MHz, specifically designed with dimensions with allow it to be installed in gardens which accommodate a reasonably-straight run of about 31.1m (102ft) for the “flat-top”. For installation in a very limited space, the dimensions of both the “flat-top” and the matching section can be divided be a factor of 2, to make the half-size G5RV, which is a very efficient antenna from 7 to 28 MHz. The full-size G5RV will also function on 1.8 MHz band if the station end of the feeder (balanced or coaxial) is strapped and fed by a suitable antenna-tuner using a good earth or counterpoise wire connection.
The full size G5RV hf antenna was not designed as a ½-wave dipole on the lowest frequency of operation, but as a 1½-wave centre-fed long-wire antenna on 14 MHz, where the 10.36m (34ft) open-wire matching section functions as a 1:1 impedance transformer, enabling the 75Ω twinlead or 50Ω coaxial feeder to see a close impedance match on that band with a consequently low SWR on the feeder. On all other hf bands the fuction of this section is to act as a section to accommodate that part of the standing-wave which, on certain of the operating frequencies, can’t be completely accommodated on the “flat-top” radiation portion. The design centre frequency for the full-size version is 14.150 khz, and the dimensions of 31.2m (102ft) is derived from the formula for long-wire antennas which is:

Length (m) = 150 ( n - 0,05 ) / f (MHz)

Length (m) = 150 ( 3 – 0.05 ) / 14.15
= 150 X 2.95 / 14.15
= 31.27

L ength (ft) = 492 ( n – 0.05 ) / f (MHz)
Length (ft) = 492 ( 3 – 0.05 ) / 14.15
= 492 X 2.95 / 14.15
= 102.57

where n = number of ½-wavelengths of the wire (flat-top).

Although some amateurs claim it may be fed directly with 50-Ω coax on several amateur bands with a low SWR, I recommended the use of an antenna tuner on bands other than 14 MHz. In fact, an analysis of the G5RV feed-point impedance shows there is no length of balanced line of any characteristic impedance that will transform the terminal impedance on the 50 to 75-Ω range on all bands. Low SWR indication with coax feed and no matching network on bands other than 14 MHz may indicate excessive losses in the coaxial line.
The above reasoning does not apply to the use of the fullsize G5RV hf antenna on 1.8MHz, or to the use of the ½-size on 3.5 and 1.8MHz. In these case the station end of the feeder conductors should be strapped and the system tuned to resonance by a suitable series-connected inductance and capacitance circuit connected to a good earth (counterpoise wire). Alternately, an “UNUN”-type of antenna tuner such as a “L” or “T” matching circuit can be used.
Under these conditions the “flat-top” or inverted-V portion of the antenna plus the matching section and feeder, function as a “Marconi” or “T-antenna", with most of the effective radiation taking place from the vertical, portion of the system. The “flat-top” acting as a top-capacitance loading element. However, with the system fed as described above, very effective radiation on these 2-bands is obtainable even when the “flat-top” is as low as 7.6m (25ft) above ground.