80 Meters and Up – Portable Base Matching Unit for 42 to 48 Foot Verticals and Inverted-Ls – Medium Power Version

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.

BMUs Top View QRP Portable and Med Pwr 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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80 Meters and Up – Portable Base Matching Unit for 42 to 48 Foot Verticals and Inverted-Ls – QRP Version

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.

BMUs Top View QRP Portable and Med Pwr 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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Why we use a Base Matching Unit (BMU) with End/Base-Fed Verticals and Inverted-Ls

In this article we look at the reduction in feedline loss when we use a BMU to mitigate impedance extremes at the base feedpoint of a Vertical or Inverted-L antenna.  Naturally, these antennas are worked against a proper counterpoise radial system for decent efficiency, especially on the low bands.

We look at the cases of a 42 ft antenna, and use an average of the measured and modeled feedpoint impedance to calculate feedline losses* for 50 ft of RG8x and for 100 ft LMR400.

BMUs Bottom View Portable QRP and Med Power

The BMU referred to here is:

A 9:1 UNUN for the mid and high bands
A Loading Coil, switched in instead of the UNUN, for the low bands

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Non-Resonant 25 ft Vertical with Metal Fence Counterpoise – 7 Bands

With the interest in 43 foot untuned verticals, and some of the less than accurate claims being made, I thought I’d share the results of a 25 foot untuned vertical antenna I developed a few years ago. Hopefully, I can shed some more light on its practical use, as well as show how to gain a bit more performance.

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