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!

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 in whatever he did. 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.


Handy Crystal Radio Antenna

In a ham shack, either half of a 40m inverted ' V ' 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.

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.

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.

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.

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