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.

Low Cost ½ λ Dipole
The cores are separated to get the λ/2 radiating length and then tied together with string to arrest further separation.

Telephone Drop Wire
The string could be done away with, and the λ/2 length yet maintained, using the reliable 'Underwriters Knot'.

Underwriter's 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.
______________________________

Improved 7 MHz QRP CW Rig

This QRP CW transmitter's output is of the order of 5W.

Improved 7 MHz QRP CW Rig
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.

Improved 7 MHz QRP CW Rig - Schematic
The variable capacitors, coil cores and 100Ω potentiometer are adjusted for maximum clean output.

Related post: Standard 7 MHz QRP CW Rig
______________________________

Standard 7 MHz QRP CW Rig

This rig works well even with low-activity crystals.

Standard 7 MHz QRP CW Rig
Heat sinks are required for the buffer and final transistors. The variable capacitors and coil cores are adjusted for maximum clean output.

Standard 7 MHz QRP CW Rig - Schematic
The enclosure is homebrew.

Related post: Basic 7 MHz QRP CW Rig
______________________________

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.

Basic 7 MHz QRP CW Rig - schematic
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
______________________________

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.

Simple 7 MHz QRP CW Rig - schematic
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
______________________________

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.

Simple CW Keyer
The difference is that I used two 555s instead of one 7413 for the clock and tone generator functions.

Simple CW Keyer - inside view
The paddle is made of spring strip, silver contacts, nuts, screws and bakelite pieces. The enclosure is also homebrewed.
______________________________

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'.

100W Class 'C' Amplifier
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.

100W Class 'C' Amplifier - inside top 
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.

100W Class 'C' Amplifier - inside bottom
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:

Class 'C' Amplifier Schematic
Power Supply Schematic
Class 'C' Amplifier 
Class 'C' Amplifier - Instructions
This amplifier fetched me a lot of DX contacts on 7 and 14 MHz using only simple dipole antennas.


Related post: My first Homebrew HF Transmitter
______________________________

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.

15W CW/10W AM Transmitter for 7/14 MHz
The transmitter stages are as follows:

 ECC81 - VFO on 3.5 MHz
EF89 - Buffer
EF89 - Multiplier to 7 MHz
EF89 - Multiplier to 14 Mhz
EL86 - Final with Pi tank

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:

Transmitter 
Transmitter Schematic
Power Supply cum Modulator
Power Supply Schematic
Modulator Schematic
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
______________________________