Perceptions: Trial with portable Vertical antenna (AHVD) system and Fiberglass material for dielectric support

Disclaimer: I am no expert in the field of dielectric effects on Electro Magnetic Waves and antennas. This article is just based on my experimentation to find suitability of antennas/support for my QTH requirements. Also, no commercial interest is claimed for the source materials/brands mentioned in this post.

Recently due to Covid19, working from remote has provided some advantages to me in having some quality time with family and also to spend some time in the radio hobby. In last few years, I had diminishing interest in radio from my home QTH at Bangalore due to nearby obstructing buildings and also due to heavy morning QTH conditions. However, I tried to keep some interest alive in radio during contest seasons by mostly travelling to my native QTH near Mangalore and setting up some station there.

Many new challenges there prompts me to try new ways to get signal out whatever little extent it may be. Thinking portable is a new mantra I am adapting to have some pleasure operating from places I go. One key challenge always is easy to carry and setup antenna system. Ofcourse, if NVIS communication is the purpose, simple low dipole/inverted Vee would be the best bet. However, for DX, it is low angle of radiation which is of particular interest to me. Only two ways to get such low angle radiation, one by having high dipole/yagi of some sought or secondly by deploying an efficient vertical antenna. During CQWW SSB Contest 2020, I had tried my hands at 4NEC2 antenna design software and deployed antennas at beach location with little success due to practicality of nice looking designs!. Making deployment simpler and repeatable was key to success. This year during 2021 CQWPX CW contest, I learnt that even simple vertical system can get me a bunch of QSO count required. However, it was not efficient and repeatable due to ground/elevated radial support system.

Checking internet, I came across designs of Asymmetric Hatted Vertical Dipole(AHVD) from KX4O (hamradio.me) and also commercial bravo antennas from N6BT etc. Designs looked very similar to elevated radial verticals we tried earlier, but with better supports and asymmetric loading technique. Due to lack of telescopic tubing availability, I tried to make prototype vertical using prolite tripod, kitchen cutting board, aluminum 3/4inch angles, caperlan fishing rod and bare copper wires. Just by adjusting lengths of wires as per KX4O design one could easily change bands. I made another small improvement to move down to 40mtr with ~12uH coil (adjusted by trial/error) on 20mtr dimensions as well. Though I could not make much contacts due to placement of the prototype antenna, I got some 20mtr CW DX contacts.

This is a great systems to try during field days and other portable ops for sure. Attached are few snapshots and a short video on the same.

Antenna at ~4ft level Loading coil between left leg and top vertical. ground only connected to right leg. Adjust the inductance ~12uH

I tried this antenna only for 20mtr with 6.07mtr vertical wire and 3.96mtr each horizontal wire (adjusted a bit to get lower SWR).

Following are few snapshot of my LCR meter showing reactance change with few common materials we use a support mast/junctions etc. I measured these inductive reactance changes for 1/2 inch dia loop with 4 windings.

AirCore Aluminum tube Caperlan 5mtr pole

Calcutta House Fiberglass tube Kitchen plastic cutting board 12m Fiberglass Spider pole

I felt, Caperlan pole is very close to spider pole in dielectric characteristics. Though it is very thin at the ends, bare copper wire of 1mm dia will stand straight without any issues for portable setup. For horizontal legs, I used 3mtr poles. I tested effect of Aluminum just as a conductive material reference.

My inductance measuring loop over the fiberglass material.