Ham Radio

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 11^th 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.