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The average recognized figure for ground loss, varies from 10 to 2 ohms (80 through 10 meters). Further, a ground strap to the nearest hard point is not a substitute for proper mounting! In fact, excessive and/or incorrect grounding can cause ground loops to occur, often masquerading as RFI! The one lower left depicts an incorrectly mounting style. In other words, It is the metal mass directly under the antenna, not what's along side, that counts! The drawing at right depicts the correct mounting style. Toward that goal, the most important consideration is proper Antenna Mounting. Ground losses (Rg) dominate the efficiency equation, and keeping them low is a worthy exercise. Since they're usually (not always) small compared to the other losses, we can just ignore them. Stray capacitance and conductor losses are the main ones. It should be mentioned at this point, that there are other losses combined with the input impedance. However, we can get a lot closer if we know a few basic facts about the input impedance (total losses). It should be apparent that accurately calculating efficiency can not be done with simple test tools, or anecdotal formulas commonly found on the internet. However, the change in the input impedance may be due to an increase in the radiation resistance, or to additional resistive (Q) losses in the coil, depending on where along the length the cap hat is installed. This will cause the input impedance to increase. No matter where it is placed along that length, it adds the same amount of capacitance. A good example of the complexity herein, is the addition of a cap hat.Ī cap hat adds capacitance to that portion (length) of the antenna above the loading coil.
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#Venturi flowmeter calculator mobile apps 1 mobile series#
Since these values are in series with one another, if we change one, it has an effect on the others. Unfortunately, we don't know any of these values with any certainty, although we can use an antenna analyzer to measure their total series value-the input impedance in other words. We can calculate it easily (close) enough, if we know three things: What the ground losses are, along with the radiation resistance and coil Q. Contents: Basics Ground Losses Radiation Resistance Coil Losses Calculating Efficiency Bandwidth Notes Īntenna efficiency is an elusive quantity, which is difficult to qualify.