Common mode current and coaxial feed lines

An antenna feed line is intended to convey energy from the transmitter to the antenna, and usually without giving rise to radiation itself.

The term “common mode” comes from consideration of the currents on an open two wire line, and it refers to the net  or unbalance current, ie the current that would give rise to external fields, to radiation.

This article looks at the equivalent common mode current in a coaxial transmission line.

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Speaker cable as RF transmission line

Speaker cable and similar Figure-8 twin in various sizes is popular as RF transmission line, particularly with QRP operators, especially those operating portable in the field (eg SOTA activators). Indeed, SOTA seems to have triggered a revival in the use of these cables. With the large number of online recommendations, one could be forgiven for thinking that a dipole and feed line formed entirely from #24 speaker wire is the antenna of choice.

With that in mind, this article looks at the performance of Jaycar WB1702 speaker cable, 14×0.14mm conductors (#24) with PVC insulation, cost $0.50/m.

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Wire dipole on 160m

Discussion with a correspondent recently ranged onto the effect of some conductor materials in antennas. This posting reports the feed point impedance and internal efficiency (meaning power not turned into heat in the structure divided by power input at the feed point) of a 160m half wave dipole (80m long, centre fed, 20m above average ground and using 2.6mm diameter single core wire).

Continue reading Wire dipole on 160m

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.

IF
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!