Advent of the Programmable Logic Controller

The Programmable Logic Controller or PLC, which was specially developed to cater to the needs of the automobile manufacturing industry, is robust and flexible and has proved itself capable of withstanding the demands of harsh industrial environments.

Fifty years ago, the mainstay of automatic special purpose machine control was hard-wired relay logic which was supported by electro-pneumatic/motorised timers, electromagnetic digit-wheel counters, step selectors, and latched relays.

Special purpose machines had come into being for carrying out reliable, repetitive and sequential machining operations in the mass manufacturing of automobile components.

Then came electronic logic gates, hard-wired gate modules, timers, counters and shift registers followed by basic microprocessor control which did not gain ready acceptance (resistance to change).

The first microprocessor-based PLCs catered only to logic functions using input, output, timer, counter and latch modules. Proficiency in relay logic made 'Ladder Diagram' programming / trouble-shooting easy and that enabled the take over of automatic special purpose machine control by PLCs.

Later, introduction of arithmetic and process control functions made the PLC quite versatile. Then came servo control & computer numerical control and the rest is history!

In the test and measurement field the industrial PC rules, with the support of dedicated modules for data acquisition & control including software from reputed manufacturers.
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Drake TR-4C - PTO problem

In the process of troubleshooting a faulty Drake TR-4C, years ago, the root cause was traced to a non-working PTO.

A visual examination of the mint-condition PCB revealed nothing. Component checks with a multimeter also showed nothing amiss.

Then 'Eureka'! A continuity test showed that the PTO coil was isolated from ground.

A closer examination of the PCB, with a magnifying glass, revealed a dry-solder connection at the ground end of the PTO coil.

Just one solder touch-up and the old workhorse was back in business!
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Unforgettable OM Guru - VU2GUR

I can’t believe that my good friend, OM Guru – VU2GUR, is no more.

He passed away on Saturday, 8th December 2018, after a brief illness. He was 78 years old.

OM Guru - VU2GUR
It’s been over 30 years since OM Guru and I first met. We found we had a lot in common and hit it off right away.

That led to daily HF / VHF QSOs and weekend visits to the local Sunday flea market, which he often referred to as ‘J-land’. We also exchanged that occasional shack visit to work on a homebrew project or troubleshoot a boat anchor or whatnot.

We teamed up on a few foxhunts and won a couple of them too.

OM Guru was always enthusiastic about anything related to amateur radio. He spared no efforts to help newbies come on the air. A high point for him was his gaining proficiency in satellite operation. He shared his experience with others and helped them work the satellites too.

I can never forget the good human being that OM Guru was.

May his soul rest in peace.

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Handy Crystal Radio Antenna

In a ham shack, either half of a 40m inverted ' V ' dipole antenna would come in quite handy as a usable crystal radio antenna element.

Handy Crystal Radio Antenna
However, a suitable loading coil would be required to make it resonant at the desired frequency.

Related post: Crystal Radio Antennas
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Crystal Radio Antennas

A medium wave broadcast station antenna system generally comprises a ¼ λ vertical element
and earth.

It would not be wrong to infer that such an antenna would be ideal for a crystal radio.

Crystal Radio Antenna Arrangement
However, practical reasons necessitate use of a much shorter element, with a suitable loading
coil making it resonant at the desired frequency.

Good results would be obtained with an element not shorter than 60 feet.

Related post: My first Antenna
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Crystal Radio / Piezo Earpiece Interfacing

Here's how to interface a piezo earpiece with a crystal radio.

Parallel-tuned, series-fed radio:



The earpiece is interfaced through a 33 kΩ shunt resistor. The resistor provides a path for the
detector current. The voltage drop across the resistor drives the earpiece.

Series-tuned, shunt-fed radio:   
   

The earpiece is interfaced through a 2.5 mH RF Choke to prevent its capacitance from short-circuiting the detector. The voltage drop across the detector drives the earpiece.

Related post: Makeshift Piezo Earphones
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Ideal detector for a Shunt-fed Crystal Radio

A Germanium transistor may be configured as a diode, having its forward voltage as low as 0.1 V, by just interconnecting its base and emitter.

Basic Shunt-fed Crystal Radio
It makes for an ideal detector in a shunt-fed crystal radio.

Related post: Crystal Radio Circuits - Alternative Concepts
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Some thoughts on UHF Crystal Radios

Diode capacitance

Low capacitance diodes are a must for UHF crystal radios.

It follows that they are to be so wired that the capacitance between their leads is kept to a minimum.

This does not imply that the leads are to be cut to minimum length. In fact longer leads facilitate antenna-diode impedance matching.

Antenna-diode impedance matching

Stub matching is a must for maximizing the signal strength.

Dipole with a single diode
Long diode leads may be used to form the stub.

Dipole with coil and diode
A diode length of λ/4 gives a proper match.

Folded dipole
A circular stub is best for minimum capacitance between the leads.

Dipole with single-diode circular stub
Related post: UHF Crystal Radio
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Motor problem

It was just another day at the plant.

A colleague from the neighbouring department called to say he had a problem.A replacement three phase induction motor, drawn from the stores and wired, just refused to start.

Our exchange :-

Voltage okay? 
Yes, all 3 phases terminal voltage 415V okay.

Maybe an overload or single-phasing. Does the overload relay trip?
No.

In that case it has no winding!
You crazy?!

No!
Okay, I'll check.

A little later the telephone rang again.

How did you guess?!

It turned out that someone in the motor rewinding department had sent an unwound motor back to the stores instead of a rewound one!
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Some thoughts on shack earthing

The main purpose of mains-supply-earthing (third pin) in the shack is to blow the fuse in the event of a live-chassis fault. Protection against static build-up / lightning strike is another matter altogether.

I was a SWL in the mid-1970s and the antenna I used with a Philips transistor portable receiver was a long wire at a height of about 50 feet. One summer afternoon, the receiver front end (AF117) blew right after a loud crackle of static. 

Then again, my first tube homebrew CW rig had a 3-pin mains supply plug. The antenna was a straight dipole 50 feet high. Operating on a summer afternoon, I received a jolt through my Junker CW Key and survived to hear the crash of thunder from a nearby lightning strike. I immediately yanked the twin-line feeder and threw it on the floor (upper floor of my 2 storey house). After a few moments I was surprised to see the arc from the banana plugs to the cement floor.

Those days, in our sparsely populated area, my antenna was way above other surrounding structures. During thunderstorms the static build-up on my 2m ¼ λ ground plane antenna would cause a whine in my 2m receiver as it dissipated through the front end coil to ground.

Conditions are totally different now, with my 2 storey house surrounded by high rises, cell phone towers and other structures with lightning arrestors. Problems of static build-up and lightning are a distant memory. I have not heard that static whine for years, even though I still use that ¼ λ ground plane antenna.

And my shack earth is just mains-supply-earth (third pin)!

Of course, if you live in the countryside, the lightning arrestor at the feeder entry-point, with a separate earth bonded to the mains-supply-earth, is a must.

While on the subject of bonding – a friend’s shack and attached bath had a separate safety earth, not bonded to the mains-supply-earth. His 2m antenna was mounted on a metal mast which was also separately earthed.

For reasons not known, the shack earth was open when the water heater developed a ground fault. The path of the fault current was through the floating earth wire, 2m rig, coax feeder braid, antenna mast and finally to ground, resulting in a coax cable fire. A parallel path also caused considerable damage to a Drake AC4 power supply.

Fortunately he had the presence of mind to pull the main breaker before he doused the fire. 
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Rugged 807 & 1625 tubes

The good old 807 and 1625 tubes can take a real beating.

One night decades ago, when I was working DX on CW with the shack lights off, the room suddenly lit up. The cathode-keyed 807 final was white hot! I let go of the key and cut the power.

Since I was monitoring the exciter signal, I was unaware of a break in the drive and had continued to send.

After the rig had cooled and the fault rectified, it was back to normal operation again. I still have that tube.
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Lightning jolt

It was a typical summer afternoon in the year 1977.

I was working CW on 40m - my homebrew EL84 rig feeding a straight dipole antenna with telephone drop wire as feeder.

Meanwhile the sky became overcast and there was a continuous rumble as I continued to work.

All of a sudden I received a jolt through my Junker key followed by the crash of a thunderbolt.

Without a thought I yanked the feeder off its sockets and threw it on the floor. My heart missed a beat when I saw the arc that followed between the banana plugs and the cement concrete floor.

The following morning's local newspaper headline was 'Lightning stuns football players'. It was a direct hit at the nearby football field. Fortunately only a couple of the players had fainted and there were no casualties.
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Drake TR-4C - receive problem

The old workhorse seldom gave problems on transmit.

A frequent receive problem was the receiver going dead on switching back to receive from transmit.

The problem was solved by replacing custom C145 (4 electrolytic capacitors housed in a can) with individual capacitors.

Capacitors drying out was the root cause.
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Yaesu FT-747GX / FT-757GX - failure to power up

Every Yaesu FT-747GX / FT-757GX user would have been flummoxed by the rig refusing to power up only to discover later that the MOX button had been left actuated.

It's a safety interlock to prevent the rig from going to transmit on power-up.
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Yaesu FT-747GX - PTH problems

A batch of Yaesu FT-747GX transceivers, produced in the 1990s, is plagued with PTH issues.

They show up as intermittent problems in receive and transmit and finally lead to total failure.

The faulty boards are the filter selection board (for receive) and the power module (for transmit).

In the filter selection board, faulty PTH connections result in the switching diodes failing to connect the required filter.

Similarly, in the power module, the result is a break in the drive to the bases of the driver transistors.

The solution is to solder jumper wires across the faulty PTH junctions.
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Injection moulding machine problem

It was a crisis call for a table-top injection moulding machine. Clear acrylic meter faces were being moulded and the output quality had deteriorated overnight.

The controls were fairly simple, the key ones being those for temperature control of 3 zones. Temperature setting was through potentiometers with graduated dial plates. The instruction manual had a chart listing the 3 settings for various plastics.

The easiest way to check whether the temperature controllers were working was to connect bulbs across the heating elements and observe the change in the switching while changing the settings. All 3 tested okay.

When I was mulling over the problem the owner excused himself for a while.

Then 'Eureka'! I turned the knobs fully anticlockwise and the pointers were not at 'zero'.

All I had to do then was to loosen the knobs to rectify that.

After changing back to the settings for acrylic, the machine was back in business!
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Speaker vibration/distortion

A Radio Cassette Recorder was received for repair.

The problem: Speaker vibration/distortion within days of its purchase in another city.

On opening the set, a cockroach was found perched on the back of the voice cone. It appeared to enjoy the vibration, for it wouldn't budge even with the volume turned high.

Without getting into details, out went the cockroach and along with it the vibration/distortion.

It was my fastest repair job, ever!
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My first satellite QSO

My first satellite QSO was with my good friend OM Bindu - VU2IR.

It was around 6.00pm, one evening in the early 1990s, when Bindu and I were chewing the rag on 2m and he excused himself to work through a satellite.

I was curious when he said he would work SSB via RS-12 with a 21MHz uplink and 145MHz downlink and would I care to join?

With hardly 10 minutes to go, I hurriedly set up a Yaesu FT-757GX (just serviced and ready to be delivered) with my 40m inverted 'V' dipole antenna for the uplink. My homebrew 2m converter and ¼ λ ground plane antenna would serve for the downlink, with my RCA BC312-D receiver as the tunable IF stage (see My homebrew 2m FM rig for more details). And my first satellite contact was thus established.

Fortunately, it was just the two of us and we continued our ragchew for the duration of the pass. With OM Bindu just 5km away, it was once again proved that the long way round is the short way!
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Remembering radio pioneer J.C.Bose

Here's a comprehensive article on radio pioneer J.C.Bose.

J.C. Bose: 60 GHz in the 1890s


 Interesting read.
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Crystal Radio Circuits - Alternative Concepts

 1. Parallel-tuned, series-fed configuration:

Parallel-tuned, series-fed Crystal Radio circuit

The diode-clipped parallel-resonance voltage is output to the phones. 

High-impedance diodes and phones are required to match the high impedance of the parallel-resonant 
circuit. 

This configuration is suitable for reception of distant, weaker stations.

   
2. Series-tuned, shunt-fed configuration:

Series-tuned, shunt fed Crystal Radio circuit

The diode-clipped series-resonance current is output to the phones. 

Low-impedance diodes and phones are required to match the low impedance of the series-resonant circuit. 

This configuration is suitable for reception of nearby, more powerful stations.


3. Series-tuned, shunt-fed variant:

Series-tuned, shunt-fed Crystal Radio variant

This is a variant of the above series-tuned, shunt-fed configuration. 

Using low-impedance diodes and phones, it delivers identical performance.

Related post: Parallel-tuned Compact Loudspeaker Crystal Radio
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Remembering OM Joe - VU2JA

My memories go back to a day in the year 1976 when OM Ramesh - VU2NRS and I had an eyeball QSO with OM Joe - VU2JA at his shack on # 20, Union Street, Bangalore.

It was in an imposing building with a tiled roof.  More imposing was the antenna, strung well clear of the roof, between two tall ground-mounted masts.

On the huge wooden shack table was an open-frame vacuum-tube CW rig, coax-coupled to a big open-frame transmatch mounted on the wall. Entry of the ladder-line feeder into the shack was through a ventilator high up on the wall. The sight of  the homebrew transmatch, with its neat copper coil and variable capacitors, is still etched in my memory and so is Joe’s characteristic CW sending.

OM Joe - VU2JA - Courtesy 73 Magazine
Joseph Alexander Faithful was born on 11th April 1898 in Calcutta. In the year 1914, working as a deckhand for his passage, he sailed to England to take up a course in Mechanical Engineering. But fate willed otherwise. War broke out when they neared Hamburg. Joe was also taken prisoner and released only six months after the war was over.

More on his incarceration at:

In England after his release, Joe qualified in wireless telegraphy and, after a fulfilling career, retired and settled down in Bangalore.

Joe married Hildred Joyce Dique at Karachi in the year 1934. They had no children.

More details including that of his career and ham radio activities at: http://www.ncdxc.org/newsletter/1975/DXer050675.pdf

He was an Amateur Wireless Pioneer, a member of the Old Old Timers Club, USA (OOTC # 695).

OM Joe passed away on 25th January 1985. Hildred followed on 31.10.1988, bequeathing their property, to the following in Bangalore, for religious and charitable purposes:

Little Sisters of the Poor, Missionaries for Charity, St. Michael’s Convent, Christu Seva Samaj, St. Mark’s Cathedral, Bangalore Cheshire Home, Bangalore Children’s Society, Kidwai Memorial Institute of Oncology, St. John’s Medical College & Hospital.

Memorable lives indeed.
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