Category: Antennas

(Varney 1958) described his G5RV antenna in two forms, one with tuned feeders and the more popular form with hybrid feed consisting of a matching section of open wire line and then an arbitrary length of lower Zo coax or twin to the transmitter.

(Duffy 2005) showed that the hybrid feed is susceptible to high losses in the low Zo line as it is often longish, is relatively high loss line and operates with standing waves.

Lets look at measurement of a real antenna, broadly typical of the G5RV. The antenna measured is a G5RV rigged in Inverted V form, 11m height at the apex and around 8m at the ends. The feed line is 2mm diameter copper spaced 50mm with occasional plastic insulators.

To some extent, the measurements are dependent on the environment, and whilst there will be variation from one implementation to another, the measurements provide a basis for exposing the configuration challenge.

Above is a plot of VSWR(50) essentially at the lower end of the matching section and low Zo line. The measurement is made looking into 0.5m of RG142 and a Guanella current balun that uses about 1m of 110Ω pair, it is essentially the load end VSWR of a hybrid feed were it used. Continue reading The quarter sized G5RV with hybrid feed

This article describes an antenna system for 40m based on:

• an inverted V dipole;
• Guanella 1:1 balun; and
• a ‘tuned’ length of RG6/U CCS coax.

The antenna system will be centred on 7.080MHz to suit my own operating preferences.

The coax is that featured at nanoVNA – RG6/U with CCS centre conductor MLL measurement and the matched line loss is taken from measurement as 4.1dB/100m @ 7.1MHz (all conductor loss). The feed line cost $50 for 100m incl delivery, so this project uses $12 worth of cable.

The broad concept is that the dipole is tuned a little shorter than a half wavelength to excite a standing wave on the coax. The VSWR desired is a little over 1.5, and the length of the coax is tuned so that the impedance looking into the coax is close to 50+j0Ω. “A little over” is so that the VSWR at the source end is very close to 1.5.

Above, the topology of the Inverted V Dipole with modelled current distribution in green. The apex of the dipole is at 11m and it is over ‘average ground’ (σ=0.005 εr=13). Continue reading Applying the RG6/U to a 40m Inverted V Dipole antenna

This article describes an antenna system for 40m based on:

• an inverted V dipole;
• Guanella 1:1 balun; and
• a ‘tuned’ length of RG11A/U CCS coax.

The antenna system will be centred on 7.080MHz to suit my own operating preferences.

The coax is that featured at Checkout of a roll of Commscope 4510404 CCS RG11A/U – Zoc, Zsc based MLL calculation and the matched line loss is taken from measurement as 1.2dB/100m @ 7MHz (all conductor loss). The feed line cost $99 for 305m incl delivery, so this project uses $6.50 worth of cable. The feed line is not good because it is cheap, it is good because it suits the application very well, and as a bonus, it is inexpensive.

The broad concept is that the dipole is tuned a little shorter than a half wavelength to excite a standing wave on the coax. The VSWR desired is a little over 1.5, and the length of the coax is tuned so that the impedance looking into the coax is close to 50+j0Ω. “A little over” is so that the VSWR at the source end is very close to 1.5.

Above, the topology of the Inverted V Dipole with modelled current distribution in green. The apex of the dipole is at 11m and it is over ‘average ground’ (σ=0.005 εr=13). Continue reading Applying the RG11A/U to a 40m Inverted V Dipole antenna