(G5RV Info Updated 06-27-2012)
Over the last few decades, the G5RV antenna has become one of the most popular and widely used "all around" multi-band antennas in the world. Even though it is a "compromise" antenna, it has good overall performance on most hf ham bands when used with an external tuner, and allows coax as an entry feedline to the radio equipment eliminating the need and hassle of ladder line or twinlead. It should be noted that some internal tuners just don't have enough range to "tune" it.
It was invented in 1946 by Louis Varney, whose call sign is G5RV ("SK" on June 28, 2000, age 89). Hence the name, the G5RV antenna.
The interaction between the radiating section and the feed-stub makes the G5RV usually easy to match on all-bands from 80 through 10 meters with an ordinary low-cost antenna tuner.
In spite of small size, it provides "almost" dipole equivalent coverage on 80 and 40 meters. From 20 on it favors DX with four to six low angle lobes reaching out in all directions which makes it a very popular antenna on the higher frequency bands. Many hams swear by them and many swear AT them due to tuning difficulties that some have.
THE ANTENNA LENGTH :
492 x ........N - 0.05 = 3 - 0.05 = 2.95 ("N" is the number of 1/2 wave lengths)
Continuing with the formula:
492 x 2.95 = 1451.4
1451.4 / 14.15mhz = 102.57 feet total length (51 feet per half rounded off)
The antenna does not need to be put up as a flat-top (horizontal fashion), but can be installed as an inverted-V.
THE ALL IMPORTANT MATCHING SECTION :
"TV" Twin Lead :
MATCHING SECTION LENGTH :
Let's use TV type twinlead in ours.
So.....Length in feet for matching section (total) = 492 X .82 / Fmhz =
492 x .82 = 403.44
403.44 / 14.15mhz = 28.51 feet for TV type twinlead
Band characteristics of the G5RV:
3.5Mhz. On this band each half of the "flat-top" plus about 17ft (5.18m) of each leg on the matching-section forms a shortened or slightly folded up half-wave dipole. The rest of the matching-section acts as an unwanted but unavoidable reactance between the electrical center of the dipole and the feeder to the antenna tuner. The polar diagram is effectively that of a half wave antenna.
7Mhz. The "flat-top or horizontal section" plus 16ft (4.87m) of the matching section now functions as a partially-folded-up "two half-wave in phase" antenna producing a polar diagram with a somewhat sharper lobe pattern than a half-wave dipole due to its colinear characteristics. Again, the matching to a 75 ohm twinlead or 50/80 ohm coaxial feeder at the base of the matching section is degraded somewhat by the unwanted reactance of the lower half of the matching section but, despite this, by using a suitable antenna tuner the system loads well and radiates very effectively on this band.
10Mhz. On this band the antenna functions as a two half-wave in-phase collinear array, producing a polar diagram virtually the same as on 7mhz. A reactive load is presented to the feeder at the base of the matching section but, as for 7mhz, the performance is very effective.
14Mhz. At this frequency the conditions are ideal. The "flat-top" forms a three-half-wave long center-fed antenna which produces a multi-lobe polar diagram with most of its radiated energy in the vertical plane at an angle of about 14 degrees, which is very effective for dx working. Since the radiation resistance at the center of a three-half-wave long-wire antenna supported at a height of half-wave above ground of average conductivity is about 90 ohm, and the 34ft (10.36m) matching section now functions as a 1:1 impedance transformer, a feeder of anything between 75 and 80 ohm characteristic impedance will "see" a non-reactive (ie resistive) load of about this value at the base of the matching section, so that the vswr on the feeder will be very nearly 1:1. Even the use of 50 ohm coaxial feeder will result in a vswr of only about 1.8:1. It is here assumed that 34ft (10.36m) is a reasonable average antenna height in amateur installations.
18Mhz. The antenna functions as two full-wave antennas fed in phase; combining the broadside gain of a two-element collinear array with somewhat lower zenith angle of radiation than a half-wave dipole due to its long-wire characteristic.
21Mhz. On this band the antenna works as a "long-wire" of five half-waves, producing a multi-lobe polar diagram with very effective low zenith angle radiation. Although a high resistive load is presented to the feeder at the base of the make-up section, the system loads very well when used in conjunction with a suitable antenna tuner and radiates very effectively for dx contacts.
28Mhz. On this band, the antenna functions as two "long-wire" antenna, each of three half-waves, fed in-phase. The polar diagram is similar to that of a three half-wave "long-wire" but with even more gain over a half-wave dipole due to the collinear effect obtained by feeding two three-half-wave antennas, in line and in close proximity, in phase.
4. Under certain conditions, either due to the inherent "unbalanced-to-balanced" effect caused by the direct connection of a coaxial feeder to the end of the (balanced) matching section, or other causes, a current may flow on the outside of the coaxial outer conductor. This effect may be considerably reduced, or eliminated, by winding the coaxial cable feeder into a coil of 8 to 10 turns about 6 inches in diameter immediately below the point of connection of the coaxial cable to the end of the matching section. The first and last turns should not touch and the coil should be taped securely to help prevent this. Some builders use this, some don't.
5. If you use regular TV type twinlead for the matching section, it's probably a good idea that you do not run much over 100 watts of power due to high swr on the feedline. Do not tape the matching section to a metal mast or pole.
Conclusions based on comprehensive research by VK1OD (website deactivated)
Suggest balanced line matching section of 9.85m (32.31 feet) of Wireman 554, extended by 15.15m (49.47 feet) of RG6/U coaxial cable to a "local" tuner. (Local tuner means tuner in the shack)
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