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.

G5RV-antenne

Bij nazicht van de antennes bleek de G5RV-antenne niet meer betrouwbaar te zijn. Dan maar de antenne naar beneden gehaald en jawel, de aansluiting van de symmetrische voedingslijn was half doorgeroest. Terwijl de antenne neerlag hebben we eveneens de afmetingen opgenomen. Lengte van de straler L1 = 30,98m. Lengte van de symmetrische voedingslijn L2 = 9,29 m.
Als we het antennehandboek van Rothammel raadplegen, dan vinden we, L1 = 31,2m en L2 = 10,3m. De G5RV-antenne resoneert op coax f = c/l . 3/2 .V = 14.062 Mhz. Onze antenne resoneert op 14,162 MHz. - De verkortingsfactor V: de praktische lengte is iets kleiner dan de theoretische vermits de elektromagnetische golven zich trager verplaatsen in de draad dan in de ether. V hangt af van: 1) De dikte van de draadgeleider. 2) De omgeving. 3) Het eindeffekt(capaciteit van de uiteinden t.o.v. de aarde).
Voor decametrische draadantennes neemt Rothammel V = 0,95 en voor een symmetrische voedingslijn is V = 0,975. - De faktor 3/2 is nodig omdat de straler drie halve golflengten lang is. Bemerk dat in het midden de stroom maximaal is en de spanning minimaal. De impedantie in het voedingspunt Z = U/I is dan laag en volgens Rothammel = 100 Ω zuiver Ohms. Op het einde van de symmetrische leiding ( Zo=300Ω ) met een lengte = l/2 is de impedantie 75 Ω , zodat we daar ’n coax kabel van 50 Ω mogen aansluiten (met toelaatbare staande golf verhouding). Een balun met verhouding 1/1 is niet aanwezig en heeft ook weinig zin, want deverhouding is enkel juist op de 14 MHz! Op de 20m band is er dus geen impedantieaanpassing nodig ! Voor de andere banden evenwel is de voedingsimpedantie ofwel hoogohmig ofwel reactief (capacitief of inductief ). Een impedantieaanpassing is dan welvereist . Luc -ON3CL- .

G5RV multiband antenna

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.