Components, complaints and complacency

Whilst reading a few issues of Wireless World from the world radio museum web site, I wondered about the issue that happened on my 21st birthday month. Reading the editorial rang a very loud bell! If it reads familiar to you enjoy the feeling. JB ZS6WL

We are constantly receiving letters from private individuals who are finding it impossible to obtain supplies of certain components and whose pleas to manufacturers and distributors are met with stony silence. Even the small company, not in the electronics field, which requires a special component for a one-off job—and which has the advantage of a company letter heading—sometimes receives the same treatment.

One of our correspondents, who was starting a small company, claimed he was asked for two trade references and the name of his bankers, and that was only in order to receive a catalogue!

However, component supply is the result and not the cause of the problem, the whole attitude of the electronics industry towards the private experimenter and the amateur is one of non-co-operation to the point of scorn. Why is this, when many of yesteryear’s major innovations in radio and electronics emanated from the results of work carried out on a kitchen table?

In those days the amateur and the professional (often one and the same person) were working on similar problems and there was a mutual respect. The technology has advanced in leaps and bounds since then and industry is staffed with people who more than likely do not have an amateur background and who have no appreciation of the problems and frustrations that can face anyone trying to work on his own for interest, self-education or amusement.

Because of the great amount of publicity given to electronics, and the aura of mystery surrounding it in the eyes of the layman, more people are taking a practical interest. This has led to manufacturers and distributors being bombarded with letters requesting the solution to private electronic problems, many of which are nonsensical or frivolous, and others could have been answered easily if the writer had shown a little initiative or visited a good library.

To answer all these queries would cost a company a great deal and what would they get in return? Perhaps an order for two or three components, the value of which may be less than the cost of the handling.

By making their components generally available on the retail market, to be bought by people who may not be qualified to use them, a company feels that it is inviting the sort of costly correspondence mentioned. The reason for the reticence in this respect can be understood.

All this has led to the present ultra-low status of the amateur in the eyes of industry and the reluctance of many concerns to accept small orders.

The industry does, however, have a responsibility to the public, even if it is only to maintain its own image, and attempts must be made to give assistance in genuine cases. Refusals because of a couldn’t-care-less attitude can never be justified and small losses should be accepted at times.

Manufacturers could easily set up machinery to ensure that their products can be sold on the retail market through a distributor. Because of the difficulty in assessing the possible quantities required perhaps some sort of sale or return arrangement could be operated with the distributor. At the present time many components are completely unobtainable on the retail market.

In addition, all private individuals seriously interested in electronics should put their own house in order, and as a first step may well think of joining a club. If there is not one in the area—start one. The answer to nearly all the problems likely to trouble the experimenter could be found amongst a group of people with a common aim. Particularly difficult problems could be made club projects. Benefits could be reaped in terms of central facilities, pooled test equipment, tools and literature.

A great deal of useful work can be done by a well-run organisation of this nature and the local community can benefit. For instance, club projects could aid local handicapped people, small electronic systems for local firms could be designed and constructed (power supplies, control systems, photo-electric switches etc.). Often these firms can advantageously use electronic equipment, but, because only a one-off is required, it is uneconomic to employ professionals to do the job.

The companies who supply components would, we feel sure, be more than willing to assist such organisations so long as things were done on a business-like basis. A good example of the sort of co-operation that can be achieved is to be seen in the components list for the Logic Display Aid in this issue.

From: Wireless-World 1969-06 pg69 

A Few thoughts as we start 2025

Hi I was wondering...

I was trying to remember which frequencies are 'new' and which are the 'old' ones. Then I recalled that the h.f. bands  changed 40 years ago!

So I set out to find the up to date charts and listings of our frequencies. Noting that the h.f. bands aren't the only ones to have changed over the years.

You may recall that in the start of Amateur Radio they were given "all those useless bands!" 

I have created a document that details the h.f. and V/UHF Bands for the Radio Amateurs in South Africa. It is a 'work in progress'. So comments are desired please. DO NOT PRINT IT.

Link:-  SA-ZA_Bandplans

Then if you really want to 'get into it' you can go to the new and improved SARL web site on mysarl.org.za to get the information from the 'horses mouth'. 

One thing that caught my eye the other day was the two tone oscillator. This is used to 'test' an SSB Transmitter for purity of output. This 'test' requires a "dummy load" of sufficient power rating for the full output power of the transmitter. Also a connection to the microphone input socket of the transmitter. 

 

So this circuit which originates from the ARRL book has some interesting features. 

It uses a pair of back-to-back diodes to regulate the output. I wonder if it really 'works' at that. So I shall put it on a proto board and check for distortion...

It may be 'good enough' for Amateur use but not for testing a HiFi. Recently I have come across some interesting articles and circuit for 0.001% Total Harmonic Distortion. Which of course are not for Amateur Radio but for 'purists' who believe you can hear the distortion below 0.1%! It used to be the defining factor in defining High Fidelity (HiFi).

 

Ham-Comp - before the Pi

Yes before the Raspberry Pi we had computers of all sorts. As a radio amateur I had some experience of using a microprocessor for an application. It was the 80s and RTTY was in great favour. This usually meant acquiring a teletype machine. Which the post office of the day was dumping in large quantities. These were hernia-inducing electro-mechanical machines weighing the best part of 50kg.

They also only ran at 50 Baud. Most radio amateurs were already running at faster speeds. And ASCII was just 'allowed' so long as it wasn't faster than the Posts and Telecommunications could read! So 300 bits per second of 7 bit ASCII. Packet Radio was just around the corner.

On my return from the UK with a ZX81 I unwisely mentioned this on the Johannesburg repeater. Being told that this was just a toy incapable of doing much. I should buy an Apple which could do much more. At this time CP/M personal computers were flooding the market with reasonably priced models. Much lower cost than the Apple II. With inexpensive software and adequate performance they were taking the word processing and spreadsheet market by storm. The Z80 versions were also quicker than the 8080 versions. Hard disks were starting to become available. I know you will laugh when I tell you the size of 5 Megabytes was considered enormous by us then.

So onto this scene came the low cost ZX81 later the Z80 based 'Spectrum'. Both had reliability 'issues' with the back connector. Which always seemed to fail at the worst possible moment. But onto this connector could be plugged all sorts of 'peripheral' cards/adapters.

As I was working at a company that had just invested in an 8080 development machine, I started taking an interest in the microprocessor. This unit had an EPROM programmer as part of the front keyboard and screen. This allowed you to write an assembler program [in 8080 code] and program the EPROM with the code. Hang on! How was I going to write for the Z80 based ZX81? ...

Well it wasn't easy but the assembler would allow 'define byte' inserted into the code. This is where I was exposed to 'code compatibility' in no uncertain terms. The Z80 had literally grown out of the INTEL 8080. Because the founders of Zilog had left Intel and designed the Z80 as 'replacement' for the 8080.

So the majority of the instructions were applicable to both processors. The assembler would produce a program that would run on the Z80 without problems.

With the help of a friend and colleague I programmed the ZX81 by hand. Wrote the program into an EPROM and took it home to try it...every night!

This 'project' taught me everything about the hardware interfacing with the software writing that forced me down a path I had not considered. I learnt how to set up the 8251 UART for 5 bit operation [Baudot]. I also learnt how to read and write to the registers and memory. It took a month but I did demonstrate it working to the Rand Amateur Radio Club. This used the TV screen and the ZX81 'listening' to a cassette tape of a RTTY transmission. 

I still have the sterilisation lamp I bought to erase the EPROMs. It is in the garage. I used to test the program I had written and erase the ones from the previous night. Then sit down with the Z80 Assembly Language Programming book by Lance A. Leventhal and pencil in the next bit of the program. I still have the book. 

The wires went to the PCB connector which was cut to size and a key added to ensure I didn't plug it round the wrong way. The 8251 is above the 5 Volt regulator heat sink. The crystal is the baud rate generator crystal with a DIP switch to set the required baud rate. As time went by I added another 2k of RAM as well as some 8 bit parallel ports. 

I don't think I could wire it up these days!

 A more complete picture with the connector/extender. Oh yes there was all sorts of possible expansions.

Later there were Z80 Assemblers and EPROM programmers. But this was 'hand-crafted'. The EPROM is missing probably somewhere amongst the EPROMS I still have somewhere! The program listing? I know I wrote it all into an exercise book. But again it is somewhere - to be found later...

73 ZS6WL John Brock

RAE Backgrounder Article 01

What is the most critical part of a car? The tyres. (tires in us English)

What is the most critical part of a HiFi (High Fidelity) setup ? The loudspeakers.

[We can argue about what constitutes a HiFi later.]

What is the most critical part of an amateur radio station?

It is the antenna installation. Which includes the matching circuitry in the output stage and the cable connection. We usually refer RAE students to the "maximum power transfer theorem" when discussing this. Forgetting the other bits and pieces that make up the whole installation.

When discussing a 'loudspeaker', we usually refer to it as a 'transducer'. It converts electrical signals into sound or air pressure changes. With a radio station it is similar. The radio frequency energy is transferred to an electrostatic wave (also an electromagnetic wave). In the 'very old' days this was called the 'aether'. This field fades away as you get further away from your transmitter. The magnetic field quite quickly. But the electrostatic field not as quickly.

Figure 1: From: Radio & Electronic Laboratory Handbook by Scroggie  

Most times Radio Amateurs get very concerned about 's.w.r.' (Standing Wave Ratio). And the notes also refer to this as a 'bad thing'. Essentially what you need to worry about is getting the maximum amount of power in your transmission 'out there'.

So recently with the supply of 'vector network analysers', it has become possible to measure the antenna with great accuracy. This leads to critical testing of the antenna and a very worried Amateur.

In the early part of the 20th century a current meter in the antenna wire was all that was required. Certainly the s.w.r. was an issue. But the valve power amplifier would ignore this 'reflected power'. Only when the voltage wave became extremely high and broke down insulators, was it 'noticed'!

With the advent of power transistors it became of vital interest to make sure the 'reflected power' did not damage the expensive transistors. Most CB radios in the 60's and 70's had a simple 'reflectometer' in the output connection. These would usually announce a bad s.w.r. in no uncertain terms.

s.w.r - How do you measure it?

Standing Wave Ratio is a ratio of transmitted radio frequency voltage or current, to the reflected voltage or current from the 'load'. The load is usually the antenna system. A 'dummy load' should provide a perfect match for the transmitter. That is no reflection of voltage or current. All of this is complicated by the fact that we are talking about radio frequency voltages. And the phasing of voltages and current will definitely not be 'in-phase'.

What is required is some 'directional' coupling to the circuit. To allow measurement of 'forward' r.f. at the same time as the 'reverse' r.f. . Most radio amateurs reach for a transmission line 'reflectometer'. This works fine over the h.f., 1 to 30 MHz range. As the coupling is usually quite small with regard to the wavelength. The well known example of this is the "Bird Thru-line Wattmeter."

Antenna Measurement

An alternative method is to 'measure' the antenna electrically. With h.f. it is relatively easy to build a 'bridge' which will indicate the impedance of the antenna. Note that I said 'impedance' not resistance. This is simply because most wire antennas 'look like electrically', a resonant LC tuned circuit. This is why an ATU proves very useful in matching an antenna to the transmitter. The bridge type circuit is the most common with transformer types the next most common. Recently though it seems that a lot of amateurs have lashed out and bought a VNA. The VNA has the advantage that it 'sweeps' the frequencies around the antenna resonance. Showing the resultant matching on a display. What about the 'monetary challenged' Radio Amateur? He/She will have to build a test unit to check the antenna.

Bridge Test Unit

The simplest form is a resistive bridge. With some provisos this can be fabricated in a tin box using readily available resistors. The downside to this is the fact that when the 'bridge' balances, nothing 'comes out of it'! So a simple diode detector stops working at the load matching frequency...

In the 'old days' this would use 2 to 5 Watt carbon composition resistors. Which in the 'old days' were readily available from component shops. Usually 'downtown'. Those shops have long ago closed never to be seen again. Component suppliers today will insist on 'minimum order quantities' and prices that bring a tear to your eye!

So what is the alternative? Radio Amateurs and Electronic Enthusiasts have become 'Electronic Scavengers.'

Let us see if we can't make a simple 'bridge'. Some of us and some clubs have a stock of resistors. Either bought over the years or left to the club as part of a deceased estate. So what can we use?

[I actually bought some decades ago 51 Ohm resistors.] It is highly unlikely that you will find them near you! But two 100 Ohm resistors in parallel make 50 Ohms. With twice the power handling of a single resistor. Or four 220 Ohm resistors in parallel make [erk! I had to check using a calculator!] 55 Ohms. Just remember that resistors in parallel have also 'self-capacitance'. Which when you use four in parallel makes four times the self-capacitance...

Figure 2: A 'simple' bridge

So this is the circuit of a 'simple antenna bridge'. It is really quite simple. BUT turn the transceiver power output down to a Watt. Otherwise the resistors will get hot! Maybe even burn out. So before checking or testing, connect your dummy load and turn the output power (CW) DOWN!!! [Don't have a dummy load? Another article link!]

The 'balanced' condition when the antenna is approximately equal to the 51 Ohm resistance produces the lowest signal level out of the 'bridge'. Which is why the bridge needs a Watt or so to drive the diode to provide a d.c. reading. A germanium diode is used as it has a low forward voltage for conduction. To give a reading at 'balance'.

There are of course other methods of measuring the antenna impedance. And it doesn't have to be at a set frequency. The source could be a swept oscillator covering the adjacent frequencies. This would show up any 'out of band' resonance. That could be corrected quickly. Also the antenna impedance can be measured accurately. So that the compensating reactance could be connected to get it resistive at the desired frequency.

...

NOTE

Even a Watt will go a long way. So other methods of lower power signal sources have been used over the years to reduce the chances of interference. The lower level of d.c. from the diode is usually amplified by an operational amplifier.

...

I intend adding to this article. Please let me know in the comments if you would like more information on this subject.

73 John Brock ZS6WL