Electronics and Technical resources from vu3dxr
Rothammels Antenna Book For many years, radio amateurs have been using this reference book, which has acquired a firm place in amateur-radio literature as an “antenna cookbook.” Dating back to the fifties, it has developed into a comprehensive reference book for practical use, which has been published in numerous German-language editions. In the interest of …
1:49 UNUN using two stacked FT240-43 cores for end fed halfwave antenna In order to match the end fed half wave antenna to the coaxial feeder, it is necessary to have a matching network or transmission line transformer. The coaxial feeder is likely to be 50Ω and the antenna impedance is possibly around 4000 or …
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 …
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 …
G4RAW 80M QRP CW Transmitter: The original version was built on tag strip, hence the name. For PA, we can use BD139 instead of 2SC2078. It should have good heat sink.
VK4FUQ’s optimised sloper antenna for 3.5MHz. Radiator and counterpoise radial are both one-quarter-wave in length (length in metres = 71.37/(frequency in MHz) or in feet 234/MHz). The radial should be at least 5ft (preferably about 8ft) above ground and immediately underneath the radiator. Good quality insulators are need at the top of the preferably non-conductive …
Half Rhombic antenna with counterpoise was published in RSGB Radio Communication magazine December 1996 page 62. Refer for more info about broadband terminated end fed antenna here.
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) Author : D.Prabakaran VU3DXR 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 …
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 …