On June 28, 2000, at 89 , Louis Varney , alias G5RV , rejoined the large family of silent keys hams.
To pay tribute to this famous amateur radio, I would like to present you one of the main work he shared with the ham community : the invention of the G5RV dipole antenna.
The G5RV, with its special feeder arrangement (ladder line), is a multi-band centre-fed antenna capable of very efficient operation on all HF bands, specifically designed with dimensions which allow it to be installed in gardens and other open spaces which accommodate a reasonably-straight run of 31.1m (102 ft) for the "flat-top" standard model. Louis Varney, SK…
Because the most useful radiation from a horizontal or inverted-V resonant antenna takes place from the center 2/3 of its total length, up to 1/6 of this total length at each end of the antenna may be dropped vertically, semi-vertically, or bent at some convenient angle to the main body of the antenna without significant loss of effective radiation efficiency. 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 two to make the ½-size G5RV, which is a very efficient antenna from 40 to 10m.
In contradistinction to multi-band antennas in general, the full size G5RV antenna was not designed as a ½-λ dipole on the lowest frequency of operation, but as a ½-wave centre-fed longwire antenna on the 20m band, where the 10.36m (34 ft) matching section (the open-wire or ladder line) functions as a 1:1 impedance transformer, enabling the 75 ohm Twin-Lead or 50/80 ohm coaxial cable feeder to "see" a close impedance match on that band with a consequently low VSWR on the feeder.
However, on all the other HF bands the function of this section is to act as a " make-up" section to accommodate that part of the standing-wave (current and voltage components) which, on certain of the operating frequencies, cannot be completely accommodated on the "flat-top" (or inverted-V) radiation portion.
The design centre frequency for the full-size version is 14.150 MHz, and the dimensions of 31.1m (102 ft) is derived from the formula for longwire antennas which is :
Length (ft) = 492 (n - 0.015) / f (MHz) = 492 x 2.95 / 14.150 = ~102 ft (31.1m)
where n is the number of ½-λ of the wire (flat-top).
In practice, since the whole system will be brought to resonance by the use of an antenna tuner, the antenna is cut to 31.1m (102 ft). As it does not make use of traps or ferrite beads, the "dipole" portion becomes progressively longer in electrical length with increasing frequency.
This effect confers certain advantages over a trap or ferrite-bead loaded dipole because, with increasing electrical length, the major lobes of the vertical component of the polar diagram tend to be lowered as the operating frequency is increased.
Thus, from 20m up, most of the energy radiated in the vertical plane is at angles suitable for DX working. Furthermore, the polar diagram changes with increasing frequency from a typical ½-λ dipole pattern on 80m and a 2-½-λ inphase pattern on 40 and 30m to that of a "longwire" antenna on 20, 17, 15, 12 and 10m bands. Although the impedance match for 75 ohm Twin-Lead or 80 ohm coaxial cable at the base of the matching-section is very good on 20m band, and even the use of 50 ohm coax cable results in a VSWR of only 1.8:1 on this band, the use of a suitable antenna tuner is necessary on all the other HF bands. Why ? Because on those bands the antenna plus the matching-section will present a reactive load to the feeder. Thus the use of the correct type of antenna tuner (unbalanced input to balanced output if twin-wire feeder is used, or unbalanced to unbalanced if coaxial feeder is used) is essential in order to ensure the maximum transfer of power to the antenna from a typical transceiver having a 50 ohm coaxial (unbalanced) output.
Also to satisfy the stringent load conditions demanded by such modern equipment employing an ALC system which "senses" the VSWR condition presented to the solidstate transmitter output stage so as to protect it from damage which could be caused by a reactive load having a VSWR of more than about 2:1.
The above reasoning does not apply to the use of the full-size G5RV antenna on the 160m band, or to the use of the ½-size version on 80 and 160m. In these cases 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 or counterpoise wire. Without this change, all your emitting power will be converted in heat before reaching the antenna...
Alternately, an "unbalanced-to-unbalanced" type of antenna tuner such as a "T" or "L" matching circuit can be used. Under these conditions the "flattop" (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, or near vertical, portion of the system; the "flattop" acting as a top-capacitance loading element. However, with the system fed as described above, very effective radiation on these two bands is obtainable even when the "flat-top" is as low as 7.6m (25 ft) above ground.
To pay tribute to this famous amateur radio, I would like to present you one of the main work he shared with the ham community : the invention of the G5RV dipole antenna.
The G5RV, with its special feeder arrangement (ladder line), is a multi-band centre-fed antenna capable of very efficient operation on all HF bands, specifically designed with dimensions which allow it to be installed in gardens and other open spaces which accommodate a reasonably-straight run of 31.1m (102 ft) for the "flat-top" standard model. Louis Varney, SK…
Because the most useful radiation from a horizontal or inverted-V resonant antenna takes place from the center 2/3 of its total length, up to 1/6 of this total length at each end of the antenna may be dropped vertically, semi-vertically, or bent at some convenient angle to the main body of the antenna without significant loss of effective radiation efficiency. 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 two to make the ½-size G5RV, which is a very efficient antenna from 40 to 10m.
In contradistinction to multi-band antennas in general, the full size G5RV antenna was not designed as a ½-λ dipole on the lowest frequency of operation, but as a ½-wave centre-fed longwire antenna on the 20m band, where the 10.36m (34 ft) matching section (the open-wire or ladder line) functions as a 1:1 impedance transformer, enabling the 75 ohm Twin-Lead or 50/80 ohm coaxial cable feeder to "see" a close impedance match on that band with a consequently low VSWR on the feeder.
However, on all the other HF bands the function of this section is to act as a " make-up" section to accommodate that part of the standing-wave (current and voltage components) which, on certain of the operating frequencies, cannot be completely accommodated on the "flat-top" (or inverted-V) radiation portion.
The design centre frequency for the full-size version is 14.150 MHz, and the dimensions of 31.1m (102 ft) is derived from the formula for longwire antennas which is :
Length (ft) = 492 (n - 0.015) / f (MHz) = 492 x 2.95 / 14.150 = ~102 ft (31.1m)
where n is the number of ½-λ of the wire (flat-top).
In practice, since the whole system will be brought to resonance by the use of an antenna tuner, the antenna is cut to 31.1m (102 ft). As it does not make use of traps or ferrite beads, the "dipole" portion becomes progressively longer in electrical length with increasing frequency.
This effect confers certain advantages over a trap or ferrite-bead loaded dipole because, with increasing electrical length, the major lobes of the vertical component of the polar diagram tend to be lowered as the operating frequency is increased.
Thus, from 20m up, most of the energy radiated in the vertical plane is at angles suitable for DX working. Furthermore, the polar diagram changes with increasing frequency from a typical ½-λ dipole pattern on 80m and a 2-½-λ inphase pattern on 40 and 30m to that of a "longwire" antenna on 20, 17, 15, 12 and 10m bands. Although the impedance match for 75 ohm Twin-Lead or 80 ohm coaxial cable at the base of the matching-section is very good on 20m band, and even the use of 50 ohm coax cable results in a VSWR of only 1.8:1 on this band, the use of a suitable antenna tuner is necessary on all the other HF bands. Why ? Because on those bands the antenna plus the matching-section will present a reactive load to the feeder. Thus the use of the correct type of antenna tuner (unbalanced input to balanced output if twin-wire feeder is used, or unbalanced to unbalanced if coaxial feeder is used) is essential in order to ensure the maximum transfer of power to the antenna from a typical transceiver having a 50 ohm coaxial (unbalanced) output.
Also to satisfy the stringent load conditions demanded by such modern equipment employing an ALC system which "senses" the VSWR condition presented to the solidstate transmitter output stage so as to protect it from damage which could be caused by a reactive load having a VSWR of more than about 2:1.
The above reasoning does not apply to the use of the full-size G5RV antenna on the 160m band, or to the use of the ½-size version on 80 and 160m. In these cases 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 or counterpoise wire. Without this change, all your emitting power will be converted in heat before reaching the antenna...
Alternately, an "unbalanced-to-unbalanced" type of antenna tuner such as a "T" or "L" matching circuit can be used. Under these conditions the "flattop" (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, or near vertical, portion of the system; the "flattop" acting as a top-capacitance loading element. However, with the system fed as described above, very effective radiation on these two bands is obtainable even when the "flat-top" is as low as 7.6m (25 ft) above ground.
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