High altitude balloon – 2014-02-08

The Melbourne HAB team led by Andy, VK3YT, launched a balloon from Deniliquin in southern NSW on 08/02/2014.

It was my pleasure, and frustration to some extent, to receive some SSDV traffic from the balloon.

SSDV Live Images - Mozilla Firefox firefox 08/02/2014 , 14:05:53Above, the last pic before it burst at 37,000m (121,000′), what a great flight.

Copy was difficult, first 70cm SSDV data received at VK2OMD at a distance of 480km and due to frequency variation of about 50Hz superimposed on slower drift, packet decode rates were low.

More on the team’s work at http://projectspaceballoon.net .

Well done guys!

Design / build project: Guanella 1:1 ‘tuner balun’ for HF – #2

Second part in the series…


Common mode impedance

When baluns are used with open wire feed lines to wire antennas on HF, most commonly the main purpose is to suppress common mode current, to ensure that the current in one wire of the feed line is equal but opposite in direction to the other wire at that point.

Continue reading Design / build project: Guanella 1:1 ‘tuner balun’ for HF – #2

Design / build project: Guanella 1:1 ‘tuner balun’ for HF – #1

This is a project to design and build a Guanella 1:1 (current) balun for use on HF with wire antennas and an ATU.

First part in the series…


For use with a tuner, the most important design criteria are:

  • high voltage withstand;
  • high common mode impedance;
  • generous power handling given our 400W PEP limit, possibly 1kW in the future.

Continue reading Design / build project: Guanella 1:1 ‘tuner balun’ for HF – #1

An inexpensive current limiter for flashing and initial testing of ESCs – Mk I

There is a risk of damage when flashing ESCs. It accrues from the fact that ESCs have a three legged H bridge and if a high and low FET are turned on simultaneously, damaging currents may flow. In fact, this can be an issue if the FETs are on together for just microseconds on each PWM cycle. Loading the wrong hex module is a recipe for disaster, it may turn on FETs in an unexpected way.

Continue reading An inexpensive current limiter for flashing and initial testing of ESCs – Mk I

Tricopter build – 20140123

My first tricopter build is based on a frame from Hobbyking. they say:

Designed from the ground-up by our own engineering team, the X900 Tricopter is a culmination of months of design, testing and material sourcing to provide you with the perfect mix of quality, performance and value.

Oh well, with hype like that, the reality can only fall short!

The size is 820mm diagonal between motor shafts (not 900mm as the type suggests).

Key elements of the configuration are:

  • Hobbyking X900 tricopter frame;
  • Turnigy D3530-14 1000kv Brushless Motor;
  • Hobbywing Skywalker 4S 40A ESC, loaded with BLHeli v11.0;
  • HK 11×4.5 SF two blade propellers;
  • Hextronic MultiWii 328P Flight Controller w/FTDI & DSM2 Port;
  • FRSKY V8FR-II HV receiver;
  • Battery monitor;
  • Turnigy Discovery Beeper
  • Zippy 3000mAh 3S 30C LiPo battery;
  • Turnigy 9XR/OpenTx transmitter.

The frame has had its problems.



The springs used for the “shock absorbing landing legs” are low grade and straighten out when stretched by the legs, see above. Fundamentally, the leg design is flawed, the spring fouls the recommended tail servo and it fouls the mounting screws at the end of the tricopter arms.


The replaced plated steel springs were placed under the inboard arm mounting nut and washer and onto one of the pins in the leg assembly, see above. They don’t found anything in this configuration. The shock absorbing leg folds up so that the servo bracket etc take the bump when the tricopter lands… the most delicate part of the whole craft is unprotected. A temporary measure is some foam zip tied to the legs, but the whole shock absorbing leg is proving to be a bit of a worthless gimmick.

The kit lacked appropriate screws to fix the servo to its bracket and the servo crank to the ball link crank, in my case some 2mm hex head screws and nuts were used.

The one part of the frame that seems well done is the tail servo bearing and motor support. The system is free of backlash, and control is stable.

The ESCs were unwrapped, cables and JST-1.0mm attached to the C2 pads as permanent programming cables and longer motor wires fitted, re-wrapped and loaded with BLHeli Multi v11.0. The ESC was given a bench test on some challenging motors at 4S, and it was very responsive with no hint of sync problems.

The FC was loaded with Mutliwii 2.3 configured for a tricopter.

Initial flights have been good, the craft has plenty of power on a flat battery, is quite responsive for such long arms, and quite stable though tuning work continues. Expectation is that a 4S battery will allow carrying camera payload should that transpire.

More when it is tuned!

Are radio hams ‘makers’

As a prelude to this discussion, let us visit the meanings of maker and ham radio or Amateur Radio as it is more formally known.

What is ‘maker’

Wikepedia offers:

The maker culture is a contemporary culture or subculture representing a technology-based extension of DIY culture. Typical interests enjoyed by the maker culture include engineering-oriented pursuits such as electronics, robotics, 3-D printing, and the use of CNC tools, as well as more traditional activities such as metalworking, woodworking, and traditional arts and crafts. The subculture stresses new and unique applications of technologies, and encourages invention and prototyping.[1] There is a strong focus on using and learning practical skills and applying them creatively.

Though it might appear to be an unorganised amateur activity, there are commercial interests in publishing, conferencing and shopfronts active in the space.

What is ham radio

Amateur Radio is defined in the International Telecommunications Union (ITU-R) Radio Regulations (RR) Article 1:

1.56 Amateur service: A radiocommunication service for the purpose of self-training, intercommunication and technical investigations carried out by amateurs, that is, by duly authorised persons interested in radio technique solely with a personal aim and without pecuniary interest.

This is an important definition because most nations subscribe to ITU-R, and it is this definition of ham radio that continues to commit large radio spectrum resource to Amateur Radio, much of it exclusively. If we devalue the ITU-R definition, we might just devalue the very reason for continued access to the amateur bands.

Though called Amateur Radio, there are commercial interests in lobby organisation, publishing, conferencing, equipment manufacture and retailing focused on the market.

Evolution of ham radio

There is very little in the way of sound research into what constituted ham radio over the hundred years of its existence. This article depends mainly on perceptions of one ham active since the late 1960s.

Tony Hancock as the radio ham, satire but too true!

There is no doubt that in times past, radio amateurs were at the forefront of developing technology in electronics, especially applied to radiocommunications. In the 1980s for example, many of the innovators in computing technology were licenced radio amateurs and it was not unusual to see their ham call sign mentioned.

Prior to the WWII, hams depended heavily on home-made equipment, and even to some extent home-made components though there was a burgeoning industry in supply components to the market. Key to this activity was that most hams understood how the equipment worked, and had probably built their equipment, and may well have designed the equipment. Hams would talk to each other on air, testing systems, validating system performance and importantly exchanging ideas, sharing knowledge.

WWII caused suspension of ham radio activity in the traditional sense, and many western nations suspended or cancelled ham licences.

Following WWII, ham radio became active again and the traditional ‘home brew’ nature of most stations was supplemented by the supply of military disposals, some of which was used directly but most was modified to a greater or lesser extent to suit ham radio and for performance improvements. The disposals equipment was readily available and cheap, especially when it was less than a complete working system, and was a ready source of cheap components so quite a lot was stripped for parts which were then used in system elements like receivers and transmitters designed by the individual ham or perhaps copied from one the ham radio handbooks or journals. There was a vibrant community sharing ideas, swapping parts and self learning and learning from each other.

But as information and communications technologies advanced at an explosive rate through the 1980s, ham radio shifted focus from ‘home brewed’ equipment to commercial off the shelf equipment designed specifically for the ham market. In this era, newer digital techniques were being applied to generation of oscillator signals within otherwise fairly traditional receivers, transmitters, and transceivers, and equipment was evolving to fully solid state at the low to medium power level. Some might say that hams were seduced by advanced technology of off the shelf equipment, buying it and to a large extent foregoing knowledge of how it worked. Instead of being interested in how it worked, hams tended to concentrate on operating the radio. Certainly many hams would not entertain the thought of modifying the radio, it may void warranty. The transceiver was now an ‘appliance’ which was used to make on-air contact with other hams and the content of on-air discussions changed away from the technical tests and discussions.

A sizeable proportion of the ham population had evolved into principally operators, and since their interest in the technology was diminishing and had little to share in conversation with remaining technically interested hams, they focused on contests and awards. Contests and awards had their origins in recognising the skills of hams, but the contests and awards were dominated by those recognising operating skills and to some extent collecting, collecting contacts to different places, mostly distant places. A lot of contest or awards activity can be seen as like train spotting in many ways.

Contests grew and evolved, they became more frequent but specialised contests grew, and contacts transformed from a minimal duration traditional contact to mass production like contacts where in pursuit of the contest goal, the contacts did not even observe the regulatory requirements for identification of the stations. Overall, the ham community through its associations and societies rewarded this type of activity and grew the contest regime. Contesters grew to think of contests as the true ham radio activity and that it had priority over other ad-hoc contacts, that it deserved priority access to the bands and that a contest dispensed with the regulations on interference avoidance, all in the pursuit of an award.

Today, the most popular activities in ham radio are:

  • contesting, operating awards pursuits and other train-spotting like activities; and
  • ‘rag chewing’, social chat about anything, well anything except meaningful discussion of radiocommunications technology (a bit like CB really, just a little more polite), usually in organised ‘nets’.

In some countries (notably the US), many hams are involved in community emergency communications networks.

Most equipment that is used is commercial off the shelf equipment, not only the electronics but antenna systems are widely purchased ready to use rather than made from basic materials like wire, tube, insulators etc.

There remains an undercurrent of technical experimentation, exchange of ideas, pursuit of the science associated with radiocommunications, but it is a dying activity (literally) and spurned on air in favour of scheduled nets where participants appear more concerned with having their say in turn than what was said by others. These ‘transmit only’ nets claim large slices of some bands to the point that it can be difficult to find a clear spot.

So whilst burgeoning hobby activities like robotics, high altitude balloons, 3D printing, CNC machining, laser cutting, RC models, UAVs etc incorporate a significant element of electronics, ham radio has relegated itself to the backwaters of electronics hobbies as more hams become just operators in a social communications network.

So, are hams makers

Ham radio or Amateur Radio organisations, as they try to make attachments or links to other activities in the hope that it somehow will supplement the declining relevance of ham radio in a technologically rapidly advancing world pitch that ham radio is a maker culture.

It might have been once, but the majority of hams today would not qualify as makers, people who think otherwise are living in a past time or simply opportunistic recruiters of would-be members for their organisation.

If you join the ranks of hams, you will find them wishing you ‘good DX’ meaning good luck in contacting a rare and distant station… but that might seem a strange principal goal when you can pull out a smart phone and have a video call to someone on the other side of the planet.

The thing that is rare is a ham who also qualifies as a maker!

I2C – LCD interface – Type 1

A range of inexpensive serial to Hitachi style LCD interfaces are becoming available.

This article describes the settings for one sold by NYplatform on eBay (about $25 for 5 inc post at the time of writing – but they are getting cheaper). It uses the Philips PCF8574T I2C expander chip which is supported by the user developed Arduino LCD Library V1.2.


Continue reading I2C – LCD interface – Type 1

Arduino RC servo ramp generator

In testing RC electric drive systems (ESC + BLDC motor), a repeatable scenario was needed to evaluate changes such as changes to commutation advance.

Often these changes have different impact under rapid acceleration or deceleration to slower changes.

This article describes a simple servo signal ramp generator based on Arduino hardware, in this case using an Arduino Nano but most Arduinos or clones could be used or adapted.

Continue reading Arduino RC servo ramp generator