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| 2m Wire Slim Jim |
connected to the BNC using the same wire. Water ingress points were sealed off with 'Araldite'.
An SWR of 1.5:1 was realized.
Related post: 2m J-Poles and a Slim Jim
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'Wire Slim Jim' for 2m
This is a 'Wire Outside PVC' Slim Jim for 2m. It was made using enamelled copper wire and a vacuum cleaner nozzzle!
The wire ends and the BNC connector were fixed with self-tapping screws. The feed points were
connected to the BNC using the same wire. Water ingress points were sealed off with 'Araldite'.
An SWR of 1.5:1 was realized.
Related post: 2m J-Poles and a Slim Jim
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connected to the BNC using the same wire. Water ingress points were sealed off with 'Araldite'.
An SWR of 1.5:1 was realized.
Related post: 2m J-Poles and a Slim Jim
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2m J-Poles and a Slim Jim
Last summer an attempt was made to homebrew a couple of 2m antennas, using parts salvaged from a disused VHF TV Yagi Beam.
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| 2m J-poles and a Slim Jim |
The moulded plastic box was used for the second version of the J-Pole. For the stub portion, the 2 elements were shorted inside the box. A BNC connector was located at the lower end of the box. A length of PVC pipe was fastened to the box to facilitate mounting of the antenna.
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| Close-up of the J-poles |
'M-Seal’(epoxy sealant in dual component lump form) was used at the joints and to waterproof the connections.
The dimensions were arrived at using 'K4ABT's J-Pole Calculator'.
Absolutely no trials / adjustments were required to get the SWR very close to 1:1!
Absolutely no trials / adjustments were required to get the SWR very close to 1:1!
With the remaining material a Slim Jim came into being.
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UHF on a VHF Rig
This circuit enables fair copy of strong 444 MHz signals, off a local repeater, using a 2m rig and an indoor 70cm ¼λ ground plane antenna.
The 300 MHz 5th harmonic of the local oscillator, mixing with the incoming signal, delivers output on 144 MHz.
The enclosure is a plastic trinket box reworked to fit two BNC sockets plus one RCA for the DC supply and also to screw the cover in place.
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| UHF Converter |
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| UHF Converter - Schematic |
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| UHF Converter - inside view |
The converse (VHF on a UHF Rig) is also possible by just changing over to a 2m antenna and a 70cm rig.
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A ¼ λ Ground Plane for 70 cm
It is easy to homebrew this ¼ λ ground plane antenna for 70cm. All one needs is a TNC connector (see inset), 1.6mm brass brazing rod and a pack of ‘M-Seal’(epoxy sealant in dual component lump form).
Radiating element length in inches is 2808/f MHz minus the projecting length of the TNC hot end.
Radial length in inches is 2950/f MHz plus a little for soldering on to the TNC connector flange.
The soldered points are sealed against water ingress using M-Seal.
Related post: Coax Collinear for 70 cm
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| ¼ λ Ground Plane for 70 cm |
Radial length in inches is 2950/f MHz plus a little for soldering on to the TNC connector flange.
The soldered points are sealed against water ingress using M-Seal.
Related post: Coax Collinear for 70 cm
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Fox Hunt Attenuator
Here's the circuit of my homebrew fox hunt attenuator.
It's a simple offset attenuator with a low part count.
The potentiometer is used to vary the signal strength of the attenuated signal, available at +1MHz, +2MHz, -1MHz, -2MHz of the fox frequency.
This attenuator was successsfully employed at a couple of fox hunts in Bangalore.
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| Offset Attenuator - Schematic |
The potentiometer is used to vary the signal strength of the attenuated signal, available at +1MHz, +2MHz, -1MHz, -2MHz of the fox frequency.
This attenuator was successsfully employed at a couple of fox hunts in Bangalore.
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Coupling a commercial VHF handheld to an external antenna
Some good commercial VHF handhelds have only one drawback - no external antenna connector.
Modification is also a problem as the rubber ducky is either integral or screwed on to a threaded stud, with no access to ground.
The result is a frustrated, repeater-bound ham. When a fellow ham in such a predicament set me pondering, realisation dawned that another rubber ducky could be used to couple the rig to an external antenna.
My own rig (which has a BNC connector!) was used to check it out. The coupling rubber ducky was mounted on the input of a homebrew SWR meter, with a dial lamp loading the output.
Modification is also a problem as the rubber ducky is either integral or screwed on to a threaded stud, with no access to ground.
The result is a frustrated, repeater-bound ham. When a fellow ham in such a predicament set me pondering, realisation dawned that another rubber ducky could be used to couple the rig to an external antenna.
My own rig (which has a BNC connector!) was used to check it out. The coupling rubber ducky was mounted on the input of a homebrew SWR meter, with a dial lamp loading the output.
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| Rubber ducky coupling to a dial lamp |
The glow of the dial lamp indicated a coupling efficiency of about 20% (2.5W to 0.5W).
A 2m external antenna was then connected instead of the dial lamp.
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| Rubber ducky coupling to an external antenna |
On-the-air tests were successful. Comfortable simplex QSOs, not possible with the rubber ducky alone, were now possible.
Related post: SWR Meter - Easymatch
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Handy 1 kW HF Dummy Load
Years ago, after replacing the tubes of a Heathkit SB-200 Linear Amplifier, I was on the lookout for a dummy load to test it.
The amplifier was successfully tested, with its Pi tank circuit providing a proper match to the dummy load.
At a later date, the same exercise was repeated with a Dentron GLA-1000.
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It then struck me that a 230V ~ 1kW electric hot plate, with its heating element resistance close to 50Ω, would do.
The mains plug of the hot plate was replaced with a PL-259 before connecting it to the output of the linear amplifier.
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| Handy 1 kW HF Dummy Load |
The amplifier was successfully tested, with its Pi tank circuit providing a proper match to the dummy load.
At a later date, the same exercise was repeated with a Dentron GLA-1000.
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SWR Meter - Easymatch
The 'Easymatch' has a length of solid copper wire as its transmission line. The diode leads,
running parallel to the transmission line, double as sensing lines.
A salvaged 100µA meter is used as the indicator, along with a 47KΩ potentiometer for sensitivity adjustment.
There is no indication till a load is connected.
Related post: SWR Meter - Pencil Box
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| Easymatch |
A salvaged 100µA meter is used as the indicator, along with a 47KΩ potentiometer for sensitivity adjustment.
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| Easymatch Schematic |
Related post: SWR Meter - Pencil Box
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SWR Meter - Pencil Box
This SWR Meter is housed in a pencil box. The transmission line is a length of TV hardline. Sensing
lines are hook-up wires, run close to the centre conductor through longitudinal holes made in the foam dielectric.
A tuning indicator (salvaged from an old Philips transistor radio) is used as the indicator, along with a 47KΩ potentiometer for sensitivity adjustment.
Related post: SWR Meter - Minimatch
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| Pencil Box |
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| Pencil Box Schematic |
Related post: SWR Meter - Minimatch
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SWR Meter - Minimatch
The 'Minimatch' differs from the 'Monimatch' with respect to its transmission line (RG-58/U
used instead of stripline-on-PCB).
Two lengths of hook-up wire, running in parallel inside the braid, are the sensing lines.
A tuning indicator (salvaged from an old Philips transistor radio) is used as the indicator, along with a 47KΩ potentiometer for sensitivity adjustment.
Related post: SWR Meter - Monimatch
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used instead of stripline-on-PCB).
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| Minimatch |
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| Minimatch Schematic |
Related post: SWR Meter - Monimatch
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SWR Meter - Monimatch
This SWR Meter is identical to the 'Monimatch', published in ARRL's 'Understanding
Amateur Radio'.
It was not difficult to follow the 'stripline-on-PCB' design.
A 100µA meter reads 'forward' or 'reverse', based on the toggle switch position.
A 47KΩ potentiometer is used for sensitivity adjustment.
Related post: SWR Meter - Easymatch
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Amateur Radio'.
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| Monimatch |
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| Monimatch Schematic |
A 47KΩ potentiometer is used for sensitivity adjustment.
Related post: SWR Meter - Easymatch
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Low-cost ½ λ Dipole for HF QRP rigs
Here’s an economical dipole for simple QRP HF homebrew rigs. It’s a one-piece radiator/feeder arrangement made of surplus insulated telephone drop wire with twin copper-clad steel cores.
The cores are separated to get the λ/2 radiating length and then tied together with string to arrest further separation.
The string could be done away with, and the λ/2 length yet maintained, using the reliable 'Underwriters Knot'.
The end insulators are scrap bakelite pieces, drilled to take the wire and string. Banana plugs are used at the rig-end.
Works real good when strung high up between two trees or other supports.
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| Low Cost ½ λ Dipole |
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| Telephone Drop Wire |
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| Underwriter's Knot |
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Improved 7 MHz QRP CW Rig
This QRP CW transmitter's output is of the order of 5W.
Fairly comfortable QSOs are possible with the higher power level. The driver and the final transistors require heat sinks. The aluminium enclosure serves as the heat sink for the final.
The variable capacitors, coil cores and 100Ω potentiometer are adjusted for maximum clean output.
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| Improved 7 MHz QRP CW Rig |
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| Improved 7 MHz QRP CW Rig - Schematic |
Standard 7 MHz QRP CW Rig
This rig works well even with low-activity crystals.
Heat sinks are required for the buffer and final transistors. The variable capacitors and coil cores are adjusted for maximum clean output.
The enclosure is homebrew.
Related post: Basic 7 MHz QRP CW Rig
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| Standard 7 MHz QRP CW Rig |
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| Standard 7 MHz QRP CW Rig - Schematic |
Related post: Basic 7 MHz QRP CW Rig
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Basic 7 MHz QRP CW Rig
This is the second version of my solid-state 7 MHz QRP CW transmitter. A heatsink is required for the transistor.
The base variable capacitor is adjusted for a chirpless signal and the collector variable for maximum output (minimum collector current).
Related post: Simple 7 MHz QRP CW Rig
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| Basic 7 MHz QRP CW Rig - schematic |
Related post: Simple 7 MHz QRP CW Rig
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Simple 7 MHz QRP CW Rig
This is the schematic of my very first solid-state 7 MHz QRP CW transmitter. A heatsink is required for the transistor.
The part count is less than 10. The 1000 pF variable is adjusted for maximum brilliance of the lamp.
DX on this rig was ~1000km (VU2SL - OM Dalvir in Valsad).
Related post: Improved 7 MHz QRP CW Rig
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| Simple 7 MHz QRP CW Rig - schematic |
DX on this rig was ~1000km (VU2SL - OM Dalvir in Valsad).
Related post: Improved 7 MHz QRP CW Rig
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Simple CW Keyer
This is a homebrew IC keyer using a 7400, a 7473 and two 555s. Here's a schematic similar to the one used for this project.
The difference is that I used two 555s instead of one 7413 for the clock and tone generator functions.
The paddle is made of spring strip, silver contacts, nuts, screws and bakelite pieces. The enclosure is also homebrewed.
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| Simple CW Keyer |
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| Simple CW Keyer - inside view |
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A Homebrew 100W (DC Input) Class 'C' Amplifier
This 7/14 MHz amplifier was built as a companion to my Homebrew HF Transmitter.
It is based on an article 'A 150-Watt Amplifier', published by ARRL in their book 'Understanding Amateur Radio'.
It has two 807 tubes in parallel. The 'clamp tube' was done away with by using negative-bias-grid-block keying. Hence the unused tube-socket cutout.
I attempted using a 'receiver-type' variable capacitor for Pi tank tuning, but heavy arcing between the plates put an end to that.
The project was on hold for about six months, till I succeeded in laying my hands on the wide-spaced variable seen.
The 'receiver-type' variable for Pi tank loading, mounted under the plate/grid current meter, is not visible.
The chassis is an aluminium baking tray picked up from the neighbourhood 'pots & pans' trader!
The cutouts were made by drilling/filing with hand tools and the cover homebrewed by cutting/bending aluminium sheet.
A few coats of enamel paint, baked on the kitchen stove, gave a fairly acceptable finish to the enclosure.
Here are the design manuscripts:
This amplifier fetched me a lot of DX contacts on 7 and 14 MHz using only simple dipole antennas.
It is based on an article 'A 150-Watt Amplifier', published by ARRL in their book 'Understanding Amateur Radio'.
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| 100W Class 'C' Amplifier |
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| 100W Class 'C' Amplifier - inside top |
The project was on hold for about six months, till I succeeded in laying my hands on the wide-spaced variable seen.
The 'receiver-type' variable for Pi tank loading, mounted under the plate/grid current meter, is not visible.
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| 100W Class 'C' Amplifier - inside bottom |
The cutouts were made by drilling/filing with hand tools and the cover homebrewed by cutting/bending aluminium sheet.
A few coats of enamel paint, baked on the kitchen stove, gave a fairly acceptable finish to the enclosure.
Here are the design manuscripts:
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| Class 'C' Amplifier Schematic |
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| Power Supply Schematic |
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| Class 'C' Amplifier |
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| Class 'C' Amplifier - Instructions |
Related post: My first Homebrew HF Transmitter
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My first Homebrew HF Transmitter
It's a 15W CW/10W AM transmitter for the 40m / 20m bands, based on G3OGR - OM F.G. Rayer's
article 'QRP Transmitter for the LF Bands' published in the August 1971 issue of 'Practical Wireless'
magazine.
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| 15W CW/10W AM Transmitter for 7/14 MHz |
ECC81 - VFO on 3.5 MHz
EF89 - Buffer
EF89 - Multiplier to 7 MHz
EF89 - Multiplier to 14 Mhz
EL86 - Final with Pi tank
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| 15W CW / 10W AM Transmitter for 7/14 MHz - top inside |
It has a companion power supply cum modulator.
The modulator stages are as follows:
ECC83 - Speeech Amplifier
EL84 - Modulator
Here are the design manuscripts:
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| Transmitter |
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| Transmitter Schematic |
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| Power Supply cum Modulator |
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| Power Supply Schematic |
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| Modulator Schematic |
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| Transmitter - Instructions |
Using this transmitter, a number of CW DX stations (including a 'W' on 40m) were worked in the late 1970s. AM DX contacts were also made with 4S7 and YB0 stations.
Only simple dipole antennas were used.
Related post: A Homebrew 100W (DC Input) Class 'C' Amplifier
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My first Crystal Radio
This simple shunt-fed crystal radio uses only a OA5 diode and a pair of vintage headphones.
The DLR No.5 I.T.B.A.5 S headphones used are of the 'Balanced Armature' type and very sensitive.
Reception of the lone local 200kW 612kHz AM station, located 20km away, is quite good using a wire antenna just 60' long and earth.
External detectors may be connected through a 2-pin socket while the OA5 is disconnected through the switch provided.
Related post: Ideal detector for a Shunt-fed Crystal Radio
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| My First Crystal Radio - Schematic |
Reception of the lone local 200kW 612kHz AM station, located 20km away, is quite good using a wire antenna just 60' long and earth.
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| My First Crystal Radio |
The homebrew enclosure is of copper clad phenolic board. The centre pin of the BNC socket serves as the antenna input with a screw terminal for the earth connection. A 3-pin audio connector is used for the headphones.
External detectors may be connected through a 2-pin socket while the OA5 is disconnected through the switch provided.
Related post: Ideal detector for a Shunt-fed Crystal Radio
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My first Antenna
The 'aerial' was erected on our two storey house in the mid-1960s. It was intended for my very first crystal radio.
With electrical conduit pipes as masts, its height was about 30 feet above the ground.
The weft wire, unravelled from a length of steel mosquito mesh, was used as the conductor! The wire was quite tough for its small gauge which rendered it rather light and minimised sag.Bakelite pieces served as the insulators.
This antenna did a great job for the series of simple radios I built those days.
I now wonder how it would have performed as a long wire antenna for the HF rigs I built in later years.
Related post: Handy Crystal Radio Antenna
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| My first Antenna - details |
The weft wire, unravelled from a length of steel mosquito mesh, was used as the conductor! The wire was quite tough for its small gauge which rendered it rather light and minimised sag.Bakelite pieces served as the insulators.
This antenna did a great job for the series of simple radios I built those days.
I now wonder how it would have performed as a long wire antenna for the HF rigs I built in later years.
Related post: Handy Crystal Radio Antenna
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How I became a ham
My fascination with Radio began in the mid-1950s. Our family radio, a General Electric AC/DC valve-type tabletop set, started it all. It required a mains connection and a copper braid ‘aerial’, with cotton-covered lead-in, strung across the living room ceiling.
I was even more thrilled with the arrival of an ‘Emerson 888 Pioneer MW Pocket Radio’, as it was literally ‘wireless’!
A decade later, I got a book ‘Build your own Transistor Radios’ by mail order, not knowing there was a radio parts store across town. Likewise, I got a soldering iron, solder, flux, a diode and a transistor.
Hooking the 6V soldering iron to our car battery kick-started my preoccupation with crystal radios, antennas, earthing, TRFs, superhets, audio amplifiers and whatnot.
Meanwhile, I chanced upon an article 'G3MY Calling!' in an issue of 'Doctors Only'. OM Mike was a doctor and a ham. My father was a doctor too and I had discovered that the magazine made for interesting reading.
Mike, now no more, made a lasting impression. It was the mid-1960s and my first awareness of ham radio. I wondered if it was permitted in India.
There was yet another article, I came across, about Australian housewives keeping in touch through two-way radio.
I turned to shortwave listening, using a Philips 4-band Transistor Portable and a long wire. I also heard aircraft transmissions on 8.8 MHz AM. In the course of these activities I stumbled upon what turned out to be a QSO between two South Indian hams. I regularly monitored the transmissions and realized that ham radio did exist in India.
A few enquiries led to a meeting with OM Pai-VU2PF and OM Ramesh-VU2NRS.
Ramesh, then a teenager, readily agreed to teach me the Morse Code. His tireless efforts and his family’s active support resulted in my successfully learning the Morse Code and eventually getting my call sign in the year 1977.
I was even more thrilled with the arrival of an ‘Emerson 888 Pioneer MW Pocket Radio’, as it was literally ‘wireless’!
A decade later, I got a book ‘Build your own Transistor Radios’ by mail order, not knowing there was a radio parts store across town. Likewise, I got a soldering iron, solder, flux, a diode and a transistor.
Hooking the 6V soldering iron to our car battery kick-started my preoccupation with crystal radios, antennas, earthing, TRFs, superhets, audio amplifiers and whatnot.
Meanwhile, I chanced upon an article 'G3MY Calling!' in an issue of 'Doctors Only'. OM Mike was a doctor and a ham. My father was a doctor too and I had discovered that the magazine made for interesting reading.
Mike, now no more, made a lasting impression. It was the mid-1960s and my first awareness of ham radio. I wondered if it was permitted in India.
There was yet another article, I came across, about Australian housewives keeping in touch through two-way radio.
I turned to shortwave listening, using a Philips 4-band Transistor Portable and a long wire. I also heard aircraft transmissions on 8.8 MHz AM. In the course of these activities I stumbled upon what turned out to be a QSO between two South Indian hams. I regularly monitored the transmissions and realized that ham radio did exist in India.
A few enquiries led to a meeting with OM Pai-VU2PF and OM Ramesh-VU2NRS.
Ramesh, then a teenager, readily agreed to teach me the Morse Code. His tireless efforts and his family’s active support resulted in my successfully learning the Morse Code and eventually getting my call sign in the year 1977.
OM Ramesh - VU2NRS
Ramesh was truly intelligent, highly motivated and very mature for one so young. He was very active on 40m/20m CW/AM. Later he homebrewed a crystal filter type SSB Transmitter for 40m/20m. It was a 50W PEP all-tube version with a built-in VFO. With able support from his father, a 3-element 20m Yagi beam followed.
Unfortunately Ramesh passed away at a very young age.
As a ham, I am highly indebted to OM Ramesh and his family.
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Unfortunately Ramesh passed away at a very young age.
As a ham, I am highly indebted to OM Ramesh and his family.
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