# Tag Info

12

Remember that carriers are selling bandwidth, that’s it. Actually, they are overselling it, exactly like cable modems (but that's another story). If everyone in the coverage area of a cell tower tried to make a call at once, most of them would be unhappy. The carriers paid a boat load of money for their chunk of spectrum and their overriding goal is to ...

8

Some of both! It's normal for a linear power amplifier for HF to be something like 50% - 60% efficient. So to make 100W, the radio probably needs 170 - 200 W. There are other power draws in the radio, let's say about 20W if it's a fancy modern rig with lots of electronics and a backlit LCD. Your radio is 13.8V nominal, but it's probably rated for 13.8V +/- ...

8

You are making an unfair comparison. HTs and amateur repeaters use the same technology now as they did forever ago. If you want to compare HT performance with cell phones, compare it with one of these: In that light, I think HTs fare favorably. Modern HTs have grown more modern batteries (NiCd -> Ni-MH -> Li-ion), but the RF bits have seen about as much ...

7

The purpose of the radials is to increase the effective ground conductivity, thus reducing losses. As you propose to have 16 radials but in four groups, I'd expect the efficiency to be somewhere between 4 radials and 16 radials evenly spaced. That said, if you need to do this to work around some obstacle, then by all means do it. You can also make the ...

6

The rest (of the current) is why your transmitter requires heat sinks (and/or airflow for thermal dissipation). Linear amplifiers are usually not anywhere close to 100% efficient. A high SWR might reduce the efficiency even further. If it's a transceiver, then the receive circuitry, front panel, and transmit idle bias also takes some wattage to run.

6

I applaud you for diving into this topic. The notion of trap efficiency has been driven largely by antenna marketing FUD (Fear, Uncertainty, and Doubt) with implicative phrases such as "no lossy traps". Since then, hams have been wringing their hands at the thought of all of those losses in their favorite trap antenna. Here is a current example of such an ...

5

"The ARRL Antenna Book" uses the lumped circuit model for HF loading coils which is an inaccurate thing to do in a distributed network circuit with reflections. The helix model in EZNEC presents a much more accurate picture as does the distributed network model or Maxwell's Equations. My web page at www.w5dxp.com has a lot of information on HF loading coils,...

5

There are far more cell phone towers than repeaters. Imagine if you lived only 2 miles from a repeater. You'd probably hit it with only 1W all the time, and have no problems getting a full quieting signal. Cell phone towers are commonly even closer than that. As far as receive only, you should be able to receive for a long time on a simple battery. Perhaps ...

5

For all practical purposes, the radiation efficiency of a folded dipole versus an ordinary dipole is the same. Consider, they are essentially the same antenna. simulate this circuit – Schematic created using CircuitLab The only difference is that in the folded dipole, we've replaced the feedpoint with a short. Since the Thévenin equivalent resistance ...

5

Hoisting a vertical antenna with a balloon seems to be a fairly-common trick for Field Day. A web search for tethered balloon antenna returns many interesting results. Here are some points brought up by several of those web pages: Ordinary round weather balloons or 36" (91 cm) party balloons work okay, until the wind blows, which causes the antenna to be ...

4

Please reconsider your weather balloon hoisting scheme, at least if you plan to use helium as your lifting gas. Helium is a non-renewable resource derived from fossil fuel (natural gas wells are the only source). It migrates through all materials light enough to make good balloons, and can't be recaptured even if the balloon is recovered before significant ...

4

Given the information supplied, and no other independent measurements, you can't really tell. You could guess, by looking at the size of the antenna, which is ~3.25 wavelengths long, and figuring that it's probably such-and-such a colinear design, which should have such-and-such a directivity. But that's probably a pointless exercise, because manufacturers ...

4

The effects of using unequal length buried radials on the radiation patterns of a monopole are not very significant, as shown by the NEC4.2 analysis below.

4

There isn't a way to calculate efficiency from gain, in general. If you had the gain for every possible direction then you could integrate over the entire sphere and calculate the total radiated power and compare that to an ideal isotropic antenna. From that you could calculate efficiency since the reference isotropic antenna is 100% efficient by definition. ...

3

Below for some perspective on this topic is a NEC4.2 analysis showing the difference in performance of a 40m, 1/4-wavelength, unloaded, base-fed vertical monopole antenna system when driven against either a 5/8" OD or a 12" OD, copper-clad, 8-ft long ground rod buried in poor Earth (1 mS/m, d.c. 5). Increasing the ground rod OD up to 12" is ...

3

VERTICAL MONOPOLE, EARTH, and BURIED RADIALS as FACTORS in ANTENNA SYSTEM RADIATION EFFICIENCY Considerations: The components shown in the graphic below, and the soil where they are located/buried are elements of the complete antenna system. R-F currents flowing on/in the earth within a radius of 1/2 wavelength from the monopole as a result of its ...

3

If by “a regulated power supply” you mean specifically a non-switching one as your second paragraph, then “a regulated power supply” and “an AC/DC adapter (linear, non-switching)” are exactly the same thing. Types of power supplies There are basically only three categories of Things You Plug Into The Wall And Get DC Out: Unregulated linear power supplies. ...

3

The first part of your question seems to be about transmitter efficiency. Engineers designing transmitters must make many design compromises at any frequency. At frequencies of several gigahertz amplifier and oscillator efficiency drops tremendously, and producing even a 10-Watt signal can be a real achievement. Speaking very roughly, losses increase as ...

3

As long as the radials are symetrical it will make no noticable difference. A single radial opposite the other half of a dipole or 2 radials opposite each other will yield a reasonable pattern. The key is symetry so that the radiation pattern is not distorted. Any number of radials will do, even odd numbers, if kept symetrical. Most people agree that more ...

3

Antenna efficiency can be defined as the ratio of the radiation resistance to the total resistance of the antenna (radiation resistance, plus ohmic resistance of the antenna, plus ground losses, etc), normalized to the feedpoint impedance. If radiation resistance is the only resistance in the antenna, then it's 100% efficient. $$\text{efficiency} = \frac{... 3 Copper indeed would be better. Silver would be better yet. These materials, however, are heavier and less rigid than aluminum. So there is that. To aluminum's advantage, it can be laser cut at very high accuracy. Copper has to be water-jet cut, at lower accuracy and higher cost. Beryllium copper alloy would be stiffer, but it's a health hazard and no shop ... 2 There are a couple of ways to approximately determine the antenna Q-factor (which is related to the bandwidth) without a full 3D simulation. One is to use this MATLAB script, which determines the antenna's theoretical bounds from its polarizability. Another approximation of the Q-factor which is from the 40's is to use the Chu limit$$Q_{\text{Chu}} = \...

2

Actual realistic and therefore useful antennas are not described by simple analytic formulas where you just plug in various parameters to compute a solution. Also, these other features such as bandwidth, impedance matching, SWR is not computed from simple formulas for such antennas. They can be computed from a numerical modeling program that performs a ...

2

I'm not familiar with the practical design of such antennas (so consider this answer a placeholder until someone more knowledgeable comes along), but here are some speculations: The current density in the capacitor plates is much lower than in the connections to the capacitor, because (in a typical air-variable) there are many plates, and within each plate ...

2

Below is a NEC4.2 study comparing the fields radiated by an eighth-wave, series-fed vertical monopole driven against sets of thirty buried radials of 1/4 and 1/8 wavelength (other things equal). The X axis shows field intensity (E), and the Y axis shows elevation (Z) above a flat Earth ground plane, at a horizontal distance of 100 meters from the base of ...

2

Below is a table showing that this is not always the result, for every antenna configuration. In this case, the configuration with the lowest system SWR(50) also has the lowest system radiation efficiency. The system in this analysis using 0.5λ buried radials has higher SWR(50), with higher system gain and higher radiation efficiency than the system using 0....

2

No, minimizing the SWR at load (antenna) interface is not sufficient for the minimization of the end-to-end loss at system level (Transducer Loss). A Figure (screenshot) might be helpful for illustration. The case is for SWR=2.06 at load, implying a SWR=1.88 at the input of an example lossy transmission line (50Ω). The purple curve is the total system loss ...

1

Radiation efficiency and radiated power from a system (transmitter, feedline and antenna) are different things. Lowest SWR minimizes losses in the transmission line. Example for more power at mismatch: assume a TX with a low-impedance output, designed for termination with 50 Ohm but allowing some mismatch. With 40 Ohm load the SWR is 1.25 and the output ...

1

If by improving conductivity, you mean flooding several acres or square miles with ocean (or saltier) sea water (or via natural intrusion near a low lying shoreline or wetlands), or installing a solid copper floor several square wavelengths in size in the parking lot, yes. But some people have reported improved antenna performance by putting a metal mesh of ...

1

Calculating the current distribution on the antenna might be a way to determine the radiation resistance, but to arrive at efficiency will require incorporating loss in the equation. It will be tricky: as Cecil notes the current in the trap could be quite high. Depending on the kind of trap there may be significant dielectric losses to take into account. ...

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