Ham Radio

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, 8^th 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 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 for 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.