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Doublet antennas: G5RV antenna
The G5RV antenna has been popular for many years, providing multiband HF amateur radio operation.
The antenna was designed by Louis Varney, who held the amateur radio callsign, G5RV. The design was originally devised in 1946, but it was not until 1958 that it was published when it appeared in the July 1958 RSGB Bulletin.
Since then further notes appeared in RSGB Radio Communication in July 1984.
Over the years, the G5RV antenna has become a very popular form of antenna for many situations and several versions are commercially available, although it is relatively easy to make from wire, insulators and the feeder.
G5RV antenna basics
The G5RV antenna is an amateur radio centre fed doublet with a symmetric resonant feeder line, which serves as impedance matcher for a 50Ω coax cable to the transceiver.
There are two implementations of the G5RV antenna. The utilises 34 feet (10.36 metres) of pen wire feeder, whilst the second uses any convenient length of open wire feeder which is connected directly to an antenna matching tuning unit.
The G5RV antenna that transitions directly to 75 Ω twin cable or coax is probably the more popular and it is shown below. However when using this option it is best to incorporate a balun in the circuit. Also the transmitter will need to have a suitable tuning capability or external tuning unit by the transmitter to ensure that it can match the antenna. Although it is meant to offer a reasonable load, the actual load on some frequencies is most likely to fall outside the range of the transmitter itself.
Although the G5RV antenna with 31 feet / 10.36 metres of open wire before transitioning to twin or coax is a convenient option, another solution is to use an antenna tuning unit.
Later adjustments took account of the different type of balanced feeders that could be used:
|Feeder Type||Length (Imperial)||Length (Metric)|
|Open Wire||34 ft||10.36 metres|
|Ladder line||30.6 ft||9.33 metres|
|TV 75Ω twin||28 ft||8,53 metres|
The original G5RV antenna design included the circuit for a suitable tuning unit, although there are many tuning units that are able to provide a good match. It is necessary to ensure that there is a balanced to unbalanced transition, i.e. a balun is used.
The antenna tuning matching unit provides two functions. One is to match the impedance because. Like any antenna, it will not give an exact match. The second is to provide the balanced to unbalanced transition.
Probably the best option is to use the antenna with an external or remote tuner unit and then the run though any building can be coaxial cable with a low VSWR.
G5RV antenna operation
The G5RV antenna operates over a wide band and is able to provide a reasonable match on most of the amateur radio bands. The antenna was originally designed in 1946 when the number of bands was much less than it is now. In fact it was designed to meet the needs of the then bands: 80 metres, 40 metres, 20 metres and 10 metres. At this time, even 15 metres was not an allocated amateur radio band.
In view of the number of different bands on which the antenna operates, the way in which it works is slightly different, i.e. the number of wavelengths in each section and hence its performance.
- 3.5 MHz, 80 metres: On 80 metres the G5RV antenna uses the flat top as well as about 5 metres of the matching section to form a half wave dipole. As a result it presents a reactive load it its input.
- 7 MHz, 40 metres: On 40 metres the G5RV antenna operates using the top section plus nearly 5 metres of the matching section and it operates as a partially folded collinear array with two half waves in phase. Again the antenna presents a reactive load to any transmitter at its input.
- 10 MHz, 30 metres: On this band the G5RV operates as two half waves in phase and as a result it presents a very reactive load at the input.
- 14 MHz, 20 metres: This is said to be the band for which the antenna was originally designed. It operates as a 3 λ / 2 dipole and presents a resistive load of about 90 Ω at its input. This provided a good match to the 75 Ω coax that was widely used at the time.
- 18 MHz, 17 metres: The G5RV performs as two in phase full wave antennas which extend slightly into the feeder section. The antenna is slightly reactive, but presents a high impedance in view of the top section being fed at a high voltage point.
- 21 MHz, 15 metres: The antenna performs as as a 5 λ / 2 antenna. As it represents an odd number of wavelengths it is fed at a current node and it is only slightly reactive.
- 24 MHz, 12 metres: The G5RV performs as a slightly long 5 λ / 2 antenna and as such it is slightly reactive, but the overall impedance is not too high.
- 28 MHz, 10 metres: The antenna acts as tow 3λ / 2 sections fed in phase. It gives a high impedance load which is slightly reactive.
The antenna is very much a compromise and it presents a variety of different loads to the transmitter. Whilst this may have been acceptable in the days of vacuum tubes / valves when it was designed, modern semiconductor PAs do not like this variety of loads and an antenna tuning unit must be used.IN terms of radiation, the G5RV antenna provides performance almost equivalent to a dipole on 80 and 40 metres. On 20 metres the extended length means that the radiation lobes provide a lower angle of radiation in some direction and therefore it can favour long distance signals in the direction of the lobes as these will tend to arrive at a low angle.
G5RV performance and choice
The G5RV antenna has many advantages, but when selecting an antenna it is worth understanding all the trade-offs against the advantages.
- Multiband capability: The G5RV antenna provide a multiband capability. It is able to operate on all amateur bands between 80 metres and 10 metres.
- Simple construction: The G5RV can be made quite easily using components available from amateur radio stores and outlets.
- Low cost: It is possible to construct a G5RV antenna for very little cost - there are no high price items
- Compromise antenna: The antenna does not provide a good match on many frequencies - an antenna tuning unit is very advisable.
- Directive pattern: The directional pattern of the antenna will vary according to the frequencies in use.
The G5RV antenna has much going for it and it can provide an idea solution for many situations where a low cost multiband wire antenna is needed. The antenna has been used for many years by thousands of people and given some useful results, although the variable impedance presented to the transmitter means that with current semiconductor based transceivers an antenna tuning unit is required to keep the VSWR within tolerable levels.
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