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.
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.
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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Handy Crystal Radio Antenna |
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.
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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and earth.
It would not be wrong to infer that such an antenna would be ideal for a crystal radio.
Crystal Radio Antenna Arrangement |
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:
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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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.
It makes for an ideal detector in a shunt-fed crystal radio.
Related post: Crystal Radio Circuits - Alternative Concepts
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Basic 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.
Related post: UHF Crystal Radio
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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 single-diode circular stub |
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