Ground dependent or independent Antenna

[Hoges]

Admission: My understanding of antenna theory is minimal! Though for the past couple of days I have been trawling various radio web sites seeking an answer to the following: How does a simple 477MHz UHF 64cm whip ground dependent antenna become 'ground independent when mounted on a spring base with an elevated feed"

Background: About 11 yrs ago, I bought a GME AE4018 whip antenna 6.6dBi , approx 64cm long, covered in black heat shrink with what appears to be a coil about half way along its length. The GME catalogue describes it as "ground dependant".

The antenna came in a kit with a spring base and an 'elevated feed'. When all screwed together, the total length is some 950mm.

The base, elevated feed and antenna is listed as a kit in the current GME catalogue as AE4018K1 and is described as a "ground independent" antenna.

So, back to my question: how does the antenna become "ground independent" when attached to the elevated feed... ?

Hoping one of our resident radio gurus might have a 'simple' answer?
Thanks in advance

Hoges

[mylesaway]

Admission: My understanding of antenna theory is minimal! Though for the past couple of days I have been trawling various radio web sites seeking an answer to the following: How does a simple 477MHz UHF 64cm whip ground dependent antenna become 'ground independent when mounted on a spring base with an elevated feed"

Background: About 11 yrs ago, I bought a GME AE4018 whip antenna 6.6dBi , approx 64cm long, covered in black heat shrink with what appears to be a coil about half way along its length. The GME catalogue describes it as "ground dependant".

The antenna came in a kit with a spring base and an 'elevated feed'. When all screwed together, the total length is some 950mm.

The base, elevated feed and antenna is listed as a kit in the current GME catalogue as AE4018K1 and is described as a "ground independent" antenna.

So, back to my question: how does the antenna become "ground independent" when attached to the elevated feed... ?

Hoping one of our resident radio gurus might have a 'simple' answer?
Thanks in advance

Hoges

The difference between 'ground-dependant' and 'ground-independant' refers mainly to the mounting base.

The AE4018 antenna with its 5/16 UNF thread would have used one of these base mounts back in the days of yore.

ABL021 - GME (https://www.gme.net.au/au/accessories/abl021/)

Back in the '80/90s we used to drill a hole in the middle of roof of the Hiluxs/Landcruisers and farm machinery to use the steel roof as a earth plane for the antennas to operate properly. On one cold, very still night I picked up some other farmers working over 50k's away from us. That type of base actually worked quiet well.

However, with the advent of the fibreglass and plastic roof on trucks and machinery the 'ground-independant' antenna became a necessity. Also the common practice of mounting antennas on bullbars and mirror arms as well. None of these provide a ground plane. The best place for any UHF antenna 'ground-independant' on my D2 would be on a roof bar in the middle of the steel roof and use the roof as a 'pseudo' land plane as I understand it.

I have been doing some testing with AM/FM antennas recently.I used a magnetic base with the same 5/16 UNF and a 900mm antenna in the middle of the roof(steel) of the D2 and 600mm 'broom stick' ground-independant' on my mine bar. No real difference between them really. In the end I used a 'Y' splitter and used the original boosted antenna from the D2 and the 'broom stick' antenna boosted as well. Pick up FM stations from 40Ks away. Fairly flat terrain around here too.

Anyhow, someone more technically minded will be along shortly to explain it better...

[Graeme]

The post for the elevated feed point must be providing enough of a ground plane.