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Monthly archives: January, 2022

Circuits – LM386 Audio oscillator

LM386 Audio oscillator This one is excellent application of widely used audio amplifier IC LM386.Its output is square wave at no load condition. Its frequency is governed by supply voltage. It can be used as code practice oscillator, even as side tone for your qrp radio. The LM386 is an widely abused integrated circuit containing …

Terminated End Fed Vee Antenna (TEFV)

Terminated End Fed Vee Antenna (TEFV) Figure1 – Terminated End Fed Vee antenna   It is a travelling wave antenna, which has a constant current distribution along its length. Antennas usually used by radio amateurs are resonant standing wave types like dipoles. It is built to a specific tuned length so that a standing wave is …

Circuits – Simple Crystal Tester

Simple Crystal tester – The idea for this crystal tester circuit sprung out of the need of testing a large number of oscillator crystals lying unused in a big hobby box. testing the crystals one by one without the appropriate device would have been very slow and a time consuming task. Commercial crystal testers are …

Circuits – 40M tag QRP Transmitter

Here is another qrp cw transmitter pulled out from SPRAT back issues, which is simple to build with commonly available components from every one shack. We can subsititute 2N2222 for BC108 and BD139 for BD 131.

Antenna – Foldaway Loop antenna

This loop antenna is based on one published in one of back issues of sprat by DL1HCU. It worked well with QRP power from 20-10 metres, including WARC bands. The tuning capacitor is twin gang type salvaged from old radio.

Circuits – Pippin QRP Transmitter

This pippin QRP transmitter is basically a conventional colpitts type crystal oscillator with output taken from a low value collector load resistor  and direct coupling is made into the base of PNP transistor used as an amplifier. This simple circuit develops around one watt output with 12V as power supply.  

Circuits – Battery Low Power Indicator

Circuits – Battery Low Power Indicator – This circuit provides a flashing pilot indicator for equipment where low battery drain is essential. The LED flashes approximately once per second and total drain current is only 320 microamps.