DIY Antennas, QRP, SDR & Ham Radio Projects from VU3DXR
The inverted rhombic antenna boasts a distinctive half-rhombic configuration. Its directivity focuses toward the terminated end, enhancing signal precision. Developed by Bruce, it demands a non-conductive mast for optimal performance. This design delivers significant gain across the 50 to 70MHz bands. A non-inductive terminating resistor is essential, tailored to the RF power delivered. For SSB […]
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 […]
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 […]
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.
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. The foldaway loop antenna represents one of amateur radio’s most ingenious space-saving designs, offering impressive […]
Rockloop HF antenna for 10,15,20 metre ham bands The Rockloop HF Antenna ‘s a tuned loop antenna measuring 33 feet square (10m x 10m) designed for 15m, 20m, and 30m bands.This rock loop antenna tunes to 15 meter band with 15 to 20pf,20 meters with about 30pf, and 30 meters with about 60pf, much suitable […]
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. At the heart of this […]
This is a clever Battery low power indicator circuit designed by G3AGX that provides a visual indication when equipment is drawing power, even at very low current levels. The circuit is particularly useful for monitoring standby power consumption or confirming that equipment is actually powered on. Battery Low Power Indicator Circuit Analysis The heart of […]
The above 7 Mhz 5 Watts CW Transmitter circuit was found in one of back issues of sprat. Still i am wondering how 5 watts juiced out from this tiny crystal oscillator circuit. This classic 7 MHz CW Transmitter circuit demonstrates how effective amateur radio equipment can be built with minimal components and straightforward design […]
FM Bandstop Filter for RTL SDR The given FM band stop filter is nothing more than a simple Band stop filter for the frequency range of 88-108Mhz. FM Broadcast transmitters transmit at high power and can cause overloading and intermodulation problems on simple receivers like RTL-SDR due to its wide open front end. The said […]