The G5RV antenna

  • G5RV antenna
    G5RV antenna

 

THE G5RV ANTENNA ( PART 2 ) THEORY OF OPERATION

 

The general theory of operation follows. As I can't put the diagrams in the file, I will paraphrase the text from the ARRL "Antenna Compendium", Volume 1, which is a great book for the antenna fan (NOT A COMMERCIAL, JUST AN OBSERVATION..[WKH]). Please keep in mind that this is the THEORETICAL information, and the actual operation will depend on placement, height above ground, metal siding, power lines, trees, UFO flight patterns, Etc.

 

3.5 MHz: On this band, the antenna acts as a shortened half-wave flat-top, with about 17 ft of the total length made up by the matching section. The ramainder of the matching section introduces an unavoidable reactance to the antenna between the feedpoint and the feedline. The antenna pattern is effectively the same as a half-wave dipole on this band.

 

7 Mhz: The flat-top, plus 16 ft of the matching section makes up a partially folded up 2 half waves in phase, (collinear) antenna. The antenna pattern is somewhat sharper than a dipole because of its collinear charecteristics. The match is somewhat degraded due to the unavoidable reactance introduced by the extra length in the matching section. This reactance can be easily tuned out with an antenna tuning unit (ATU).

 

10 MHz: On this band, the antenna functions as a 2 half-wave collinear. It is very effective, but the reactance presented at the feedpoint requires a good ATU. The pattern is basically identical to the 7 MHz pattern.

 

14 MHZ: This band is where the G5RV really shines. The antenna is operating as a 3/2 wave long, center-fed antenna with a multi-lobed, low angle pattern of about 14 degrees elevation, which is very effective for working DX on this, the most popular DX band. The antenna presents a 90-ohm load with basically no reactance present. Even the use of a 50-ohm coaxial feed will present a SWR of only about 1.8:1, easily tuned out with an ATU.

 

18 MHz: The antenna performs as 2 full-waves in phase, combining a lower angle with the broadside gain of a collinear array. The load is high-Z, with somewhat low reactance.

 

21 MHz: On this band, the antenna works as a 5/2-wave, center-fed long wire. This produces a multi-lobed, low angle radiator, with a high-Z resistive load. When matched with the ATU, it makes a highly effective antenna for DX contacts.

 

24 MHz: The antenna again functions effectively as a 5/2-wave long wire, but due to the shift in the position of the current loops on the array, the load is resistive, approximating the load on 14 MHz. Again, the pattern is multi-lobed, with a low radiation angle.

 

28 MHz: On this band, the antenna acts as a 3-wave, center-fed long wire.

 

The pattern is similar to 21 or 24 MHZ, but with additional gain due to the colliner effect obtained by feeding two 3/2-wave antennas in phase. The load is high-Z, with low reactance.

 

In Part 3, I will discuss the construction of the G5RV... Keith, KE2DI