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Category «Circuits»

Ten Minute QRP Transmitter

Ten Minute QRP Transmitter The design apparently originated in 1996 in an amateur radio club QRP publication.  The name originates since the original author claimed he built this transmitter and make a QSO with it in just 10 minutes time. There are no coils to wind  it tunes a wide range of crystal frequencies, and it outputs an …

Circuits – Sovina2 40M Class E Transmitter

Adaptation of Class E amplifier for amateur radio application is very rare due to inherent difficulties in filter design associated with it till release of usdx transceivers. The above compact transmitter uses class E amplification with three BS170 mosfets, a popular approach in usdx final. What’s new is the oscillator…any similarity with the NS40 is …

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 …

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.

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 …