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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.

Circuit – FM Bandstop Filter for RTL SDR

fm trap

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 …

DIY – Making printed circuit boards

pcb making

Making printed circuit boards There are many ways to produce your own printed circuit boards. Small boards for DC switching circuits are easy to make because neither the size nor the shape of the copper foil traces is critical. Boards containing many digital ICs are considerably harder to lay out and etch. There are also …