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| Improved 7 MHz QRP CW Rig |
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| Improved 7 MHz QRP CW Rig - Schematic |
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.
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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