Linear loaded short dipole

For my amateur radio activities on the HF bands I only have a 3.6 m wide balcony available for antennas. After some study I decided to experiment with a shortened dipole for the 15 m band. The full size 21 MHz half wave dipole would require a span of approx 7 m, therefore I searched for a solution to shorten the full size length by 50 percent.

Finally I decided for a linear loaded dipole; the layout and resulting dimensions are shown below.


First measurements at the resonance frequency showed a low input impedance at the dipole’s feed point with values around 10 Ohm. The theoretical radiation resistance of a 2 x 1.6 m short dipole would be 10 Ohm, so it is an indication of low losses in the system. In order to match the antenna to the 50 Ohm of the transceiver, I use a quarter wave transmission line transformer consisting of two parallel connected 50 Ohm coaxial cables.


After fine tuning the length of the antenna wires, I achieved an SWR below 1.5 for the CW segment of the 15 m band.


The antenna’s bandwidth is around 200 kHz; I could already work DX stations around the world.

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Dipole feed point and 1:1 balun

RUMLog, Macbook and IC-718

In Singapore you need to get approval from the authorities for your type of radio, you intend to buy, before you can actually buy it. So in order to avoid any problems, I selected the ICOM IC-718 HF transceiver, as I knew it was approved before and available from stock.

Now, setting up my station, I was looking for a good logging program, running under OS-X on my new Apple Macbook (early 2015). I decided for RUMLog, as it is free and offers all features I need for my casual operation.

To connect to the IC-718, I use a Icom CT-17 CI-V CAT Programming Cable with a Prolific chip set.  The drivers can be downloaded from their support webpage and work without problem under OS X El Captain (10.11.3). Now frequency and operation mode are automatically transferred to RUMLog.


In Dec 2015 I received my amateur radio licence with the call sign 9V1KG for Singapore from the IDA. After 15 years inactivity I am back on the air.

First version of my shortened 15 m dipole. Latest version see here.

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Telescopic whip antenna

Project XE180 – Miniquad FPV

After I just completed my first own-built quad-copter, here a few details to share about this project. Having the DJI Phantom 2 V3 for aerial photography and a ready built 250 Storm racing drone, I was looking for a FPV mini-copter to fly indoor and outdoor, using brush-less motors and a robust carbon frame. My choice was XELITES ‘s  XE180, a 180 frame (motor to motor distance 180 mm).

Continue reading Project XE180 – Miniquad FPV

How fast can a quadcopter fly?


Racing drones are becoming more and more popular, and it would not only be interesting to know, how fast they can really go, but also which parameters have a major impact on their maximum speed. When I searched in the net, I couldn’t find clear answers and had to work out something by myself; so here is my model. To be clear, my intention is not to get absolute precise numbers, but more to understand the physics behind, and to have a tool to get realistic estimates and comparisons of flight parameters for different quadcopter models. If you are not interested in the details, just scroll down to the end of the page, where I show the final formulas and some calculated examples.

Continue reading How fast can a quadcopter fly?