Josh, VK2JOS and Sam, VK2AFA

We have slowly been trying to build an Echolink Access point at home to allow us to use Handheld radios in the area (around home, down at the shops etc) without having access issues to the main repeaters due to the lack of output power and antenna efficiency issues that usually come with handheld transceivers.

First issue we had was the length of the antenna at 2m so we decided to build a 70cm antenna until we can get some more material, a 9dB 70cm antenna was just short of 3 meters in length. (as pictured below)

Upon initial testing the antenna proved very impressive, testing from Thornton to Charlestown (approx 25klm as the crow flies) on Simplex against a commercially built 5.5db antenna the results were as follows

Simplex 20 Watts 70cm via 2 x Yaesu 857D Transceivers:

• Commercial 5.5dB Antenna Signal of S0-1
• Home Brew Collinear Antenna Signal of S6-7

Both Antenna’s where only mounted 3mtrs above the ground, so it would be expected that even better improvement could be made by mounting it nice and high.

Brenton, VK2MEV

Recently I constructed an end fed half wave antenna for 6m based off the “flower pot” design by VK2ZOI. This antenna design is electrically identical (in terms of radiation pattern and feedpoint impedance) to a half wave dipole however it is mechanically end fed, allowing for easy construction and mounting.

One half of the dipole is built by soldering a 1/4 wave length of wire to the center conductor of the feedline and the coax shield is used as the counterpoise. In order to “cut” the length of the counterpoise a resonant choke is wound in the feedline a 1/4 wavelength back from where the coax ends. For more theory as to how RF currents flow in this antenna I refer you to the website of Dave VK5DGR.

The size of the choke is dependent on what band the antenna is built for, a reference table is listed on VK2ZOI’s website. For 52MHz this works out to be 12 turns on a 50mm former, so PVC pipe is the perfect material for this job. The coax is fed through two ~5.5mm holes drilled in the PVC pipe to clamp it, the coax can also just be cable tied or taped while the antenna is being tuned.

The experimental antenna was mounted to a 12′ (3.7m) fishing rod which I found at K-Mart for $29. The mounting medium can be anything which is non-conductive, just so long as it is strong enough for the intended application. A flexible fiberglass rod would suit a mobile installation while 50mm PVC would be better for a home antenna.

Tuning is achieved by either cutting/lengthening the 1/4 wave wire or by adjusting where the coil starts. According to VK2ZOI an SWR of <1.5:1 can be achieved over about a 3MHz bandwidth.

The antenna has so far been tested between my QTH in Dudley and several stations around Newcastle and Maitland with Q5 reports all round. The Somersby 6m repeater is received full scale (which is to be expected as I have line of sight to the Somersby repeater site) and the VK2WI news broadcast was heard at a noisy S1 on Sunday May 5th.