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.
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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.
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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.
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
Continue reading Why we use a Base Matching Unit (BMU) with End/Base-Fed Verticals and Inverted-Ls
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Below are presented the results of actual measurements as well as EZNec modeling of both a 90 ft long End/Base-Fed Inverted-L 45 ft high and 45 ft across, as well as a 45 ft long Inverted-L 23 ft high and 22 ft across. Measurements of both were taken with a combination of a RigExpert AA-1400 and an HP8510 Vector Network Analyzer.
The 90 ft antenna is suspended by a pair of tall LobLollies, and is driven against a counterpoise system consisting of 14 surface ground radials and a low chain link fence.
Continue reading End/Base-Fed Inverted-L, 90 ft and 45 ft versions, Feedpoint Impedance and SWR
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Below are presented the results of EZNec modeling of a 45 ft long End/Base-Fed Inverted-L, 23 ft high and 22 ft across. Elevation patterns and Azimuth patterns at the peak of low angle radiation are plotted for all ham bands 80 Meters through 6 Meters.
For modeling purposes, a multi-connection distributed grounded counterpoise is used. This empirical structure provides a reasonable broadband counterpoise over the frequency range of interest.
Continue reading End/Base-Fed Inverted-L, 45 ft version, Elevation and Azimuth Radiation Plots
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Below are presented the results of EZNec modeling of a 90 ft long End/Base-Fed Inverted-L, 45 ft high and 45 ft across. Elevation patterns and Azimuth patterns at the peak of low angle radiation are plotted for all ham bands 160 Meters through 6 Meters.
For modeling purposes, a multi-connection distributed grounded counterpoise is used. This empirical structure provides a reasonable broadband counterpoise over the frequency range of interest.
Continue reading End/Base-Fed Inverted-L, 90 ft version, Elevation and Azimuth Radiation Plots
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