You may have wondered why some of us keep yammering on regarding “Common Mode Current” on the coax, and why common-mode prone designs (like end-feds and JPoles) are so problematic. Here’s an example of a 915 MHz antenna for a wideband comm system prototype I am designing. I decided on a wide-band vertical dipole.
In the pix below, we see the dipole front, and the dipole rear in it’s final form (sans heat shrink) – with a single loop binocular type 61 core performing the 1:1 current BalUn / choke function (they are the same thing):
Continue reading Why We Don’t Like Unintended Common-Mode Current Flow On Our Transmission Lines
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Apparently there are lot’s of differing opinions on antennas – now there’s a shocker Hopefully, we can put some rough numbers on things to help folks to figure out where opinion ends and basic principle begins.
Continue reading Low Gain Ground Mounted Antennas for LEO Satellites
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The 40 Meter Pixie (available at the time of writing for about $7 assembled on eBay) is an interesting minimalist transceiver design – crystal controlled, 2 transistors and an audio amplifier chip. And you are on the air with a unit that you can make QSO’s with! Naturally, there is much room for improvement, and it can in fact be done for only a few dollars more. Below I describe a set of additions that I think really enhances the Pixie’s usefulness.
Continue reading Project LOAP (Lipstick On A Pig) – Pixie XCVR Mods with Outboard CW Filter and Audio Amp
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The unit on the left below is the medium power BMU (Base Matching Unit) intended for 42 foot to 48 foot vertical, sloper, or Inverted-L antennas. Naturally, these antennas (like all end-fed antennas) require a decent radial system for efficient operation on the lower bands.
Continue reading 80 Meters and Up – Portable Base Matching Unit for 42 to 48 Foot Verticals and Inverted-Ls – Medium Power Version
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The unit on the right below is the QRP BMU (Base Matching Unit) intended for 42 foot to 48 foot vertical, sloper, or Inverted-L antennas. Naturally, these antennas (like all end-fed antennas) require a decent radial system for efficient operation on the lower bands.
Continue reading 80 Meters and Up – Portable Base Matching Unit for 42 to 48 Foot Verticals and Inverted-Ls – QRP Version
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As part of renewed interest in portable medium power operations, I wanted a small cheap matcher. The units below are simply standard T-Tuners. Using dirt-cheap construction technique and commonly available parts, these units perform well at a very low cost.
Continue reading Still More Medium Power T-Tuners for Cheap
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As part of project LOAP (Lipstick On A Pig ===> http://vtenn.com/Blog/?p=1348), I wanted a small cheap matching and SWR indication unit for the Pixie-based transceiver system. The T-Tuner and SWR bridge unit on the right, in the picture below, is not vastly different from others, but here it is for your consideration as a good performer at a low cost. Note however, that it has been characterized into real-world impedances with a worst-case loss of less than 0.9 dB.
Continue reading Yet Another QRP Portable T-Tuner and SWR Bridge for Cheap
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Often one sees characterization and loss measurement of UNUNs using an SWR measurement of the UNUN when terminated in it’s transformation resistance, or with the “back-to-back” 2-x-Loss method. Each method reveals something about some quality of the UNUN, but neither method tell us much about how much power the UNUN will deliver to the actual antenna.
In this article I will show a simple method of measuring actual UNUN losses into the actual load impedances that the UNUN will see in service.
Continue reading “Z-Substitution” Method for Measuring UNUN Loss Into Real-World Load Impedances
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Excellent technical article regarding limited space antennas:
Limited Space Antennas
Continue reading Classic W8JI Limited Space Antennas Article
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