With his low cost, high precision Vector Network Analyzer, Tom (DG8SAQ) started a revolution in Ham Radio. Thanks to his efforts, amateur (and professional!) enthusiasts have now the possibility to perform measurements which were reserved to well funded HF laboratories before. In this video, Tom explains the evolution and capabilities of his VNWA and why even NASA relies on it now as well! The presentation was held during the Ham Radio Hamfest in Friedrichshafen, Germany in June 2012.

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During the summer break it became quite here on my blog. While Instead of chilling at the beach, I spend a lot of time on new Hardware and Software projects. Most of them are done, and now it’s time to document them. In this blogpost I want to share the construction of a versatile 4:1 Balun. In combination with ladder line and an automatic Antenna tuner you can use any dipol on almost all frequencies.

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Over the last years I spent a lot of time simulating antennas. One annoyance I encountered over and over was the unavailablity of values for ground conductivity and the relative permittivity. Two figures which have quite an impact on the antenna performance, especially on vertical antennas. This finally led to the conclusion that both figures need to be measured. In early 2012 I built a measurement kit and finally determined ground conductivity and relative permittivity at our contest station.

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Last weekend I was invited to speak in the Contest Forum at HamRadio convention in Friedrichshafen, Germany. The presentation was about our Contest Activity from northern tip of Qatar. We participated in the Multi/Multi category and used almost exclusively verticals antennas. For everyone who missed the event, here are the slides! A73A CQWW 2012 Contest operation from the Desert of Qatar from Tobias Wellnitz

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Where ever I operate contest in a multi transceiver environment interferences between the 40m and 20m are guaranteed. An easy way to reduce interferences are coax stub filters. Dave, K1TTT has a great website with a lot of useful technical resources. One of them is dedicated to coax stub filters. After building up two sets of stub filters (one in Namibia at V55V and the other one in Spain at ED1R) it’s time to document it.

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In untrusted environments like open WiFi Hotspots you want to tunnel your traffic through an encrypted channel to the internet. Last year Firesheep has proven successfully how dangerous surfing in a public, non encrypted hotspot can be. A Virtual Private Network (VPN) can also be used to access internet services with IP Address restictions (e.g. Video or Music streaming services like Netflix, Hulu or Spotify). In this post I’ll show you a VPN solution which can be easily set up and used. The tutorial will work with the Windows and Mac OSX.

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Tobias Wellnitz, DH1TW


Software Engineer

Germany