question: Can someone explain to me dB levels of antennas and what is good or bad?
comment: dB by itself is a relative measurement. When someone says “that antenna has 10dB of gain” that means it has 10dB of gain as compared to another antenna, usually a plain dipole or a theoretical isotropic radiator. When you get gain out of antenna, it’s always a trade off between gain and directivity. A 0db gain antenna receives equally in all directions. A 24dB parabolic dish can’t hear well from either side or the back. You may see other terms like “dBm” which is dB as referenced to 1 milliwatt. You’ll see that a lot in the wifi world. The access points output power level measurements are usually in dBm and the received signal level is the same. So if you see your access point reporting a signal level of -95dBm, that means the signal is 95dB lower than 1 milliwatt. Or “that signal was 30dB over the noise floor” which is another relative measurement.
passages: Section::::Characteristics.
  
  The antenna's power gain (or simply "gain") also takes into account the antenna's efficiency, and is often the primary figure of merit. Antennas are characterized by a number of performance measures which a user would be concerned with in selecting or designing an antenna for a particular application. A plot of the directional characteristics in the space surrounding the antenna is its "radiation pattern".
  
  Section::::Characteristics.:Bandwidth.
   Note that in the case of an impedance mismatch, "P" would be computed as the transmission line's incident power minus reflected power. Or equivalently, in terms of the rms voltage "V" at the antenna terminals:
  
  where "Z" is the feedpoint impedance.
  
  Section::::Gain in decibels.
  
  Published numbers for antenna gain are almost always expressed in decibels (dB), a logarithmic scale. From the gain factor G, one finds the gain in decibels as:
   BULLET::::- 100 dBµ or 100 mV/m: blanketing interference may occur on some receivers
  
  BULLET::::- 60 dBµ or 1.0 mV/m: frequently considered the edge of a radio station's protected area in North America
  
  BULLET::::- 40 dBµ or 0.1 mV/m: the minimum strength at which a station can be received with acceptable quality on most receivers
  
  Section::::Relationship to average radiated power.
   BULLET::::- The receiving antenna is also typically directional, and when properly oriented collects more power than an isotropic antenna would; as a consequence, the receiving antenna gain (in decibels from isotropic, dBi) adds to the received power.
  
  BULLET::::- The antenna gains (transmitting or receiving) are scaled by the wavelength of the radiation in question. This step may not be required if adequate systemic link budgets are achieved.
  
  Section::::In radio systems.:Simplifications needed.
   Section::::Locations.:In the United States.
   It can be seen that, since the radiation resistance is usually very low, the major design problem is to keep the other resistances in the antenna-ground system low to obtain the highest efficiency.
  
  Section::::Multiple-tuned antenna.
   The radiation pattern of WWVB antennas is designed to present a field strength of at least 100 μV/m over most of the continental United States and Southern Canada during some portion of the day. Although this value is well above the thermal noise floor, man-made noise and local interference from a wide range of electronic equipment can easily mask the signal. Positioning receiving antennas away from electronic equipment helps to reduce the effects of local interference.
  
  Section::::See also.
  
  BULLET::::- Radio clock
  
  BULLET::::- Watch (electronic movements)
  
  Section::::External links.
  
  BULLET::::- – official website
   All antennas’ most intense fields are local, and rapidly diminish with distance from the antenna, so ground losses "can" be reduced or effectively eliminated if the antenna can be placed strategically far away from any electrical or magnetic obstacle. For example, very high frequency (VHF) quarter-wavelengths are about 5 feet (1.5 m), so a quarter-wave or half-wave VHF antenna is small enough to be feasibly mounted on a non-conducting mast several quarter-wavelengths above the earth and far from other antennas, metal-clad or cement buildings, or metal-frame structures.
  
  Section::::Calculation.
  
  In general, electrical power is calculated by:
   The most common antennas in this band are wire antennas such as wire dipoles and the rhombic antenna; in the upper frequencies, multielement dipole antennas such as the Yagi, quad, and log-periodic antennas. Powerful shortwave broadcasting stations often use large wire curtain arrays.
   There is some confusion over the use of the term "nominal", which is often used incorrectly to mean "average or typical". The relevant definition in this case is "as per design"; gain is applied to make the average signal level correspond to the designed, or nominal, level.
  
  Section::::Standards.
   The performance of the overall system may be improved by using matched antennas at each end of the communication link, such as those described earlier.
  
  Finally, the labeled remote distance of any particular system is normally measured in an open-air line of sight configuration without any interference, but often there will be obstacles such as walls, floors, or dense construction to absorb the radio wave signals, so the effective operational distance will in most practical instances be less than specified.
  
  Section::::Module Physical Connection.
   Section::::Reception and performance.
  
  Section::::Reception and performance.:Critical reception.
   Antennas are a common source of weak signals. An outdoor antenna is often connected to its receiver by a transmission line called a "feed line". Losses in the feed line lower the received signal-to-noise ratio: a feed line loss of degrades the signal-to-noise ratio (SNR) by .
   Antenna height considerations
  
  The Aspects for Antenna heights considerations are depending upon the wave range and economical reasons.
  
  Section::::Longwave/low frequency antennas.
   With any such receiver, a high-performance loop antenna may be employed, or in the alternative, one or more outdoor longwire "Beverage antennas", sometimes many hundreds of meters long. In order to cancel out reception of unwanted stations, some DX listeners employ elaborate "phased arrays" of multiple Beverage antennas. 
   If you are doing tests in an Anechoic or Semi-Anechoic chamber, you have to account for the conversion between dBm power in a 50ohm cable to dBuV/m electric field over the air, as well as the antenna and preamp gains and the long cable loss between the receiving chamber antenna and the spectrum analyzer. For an example calculation, see pages 13–15 of the TDK Test Report for FCC ID: YYJ-5390144, the "WUSB Host Radio Board".
  
  Section::::Practical Considerations.
   BULLET::::- Details of the overall signal quality (normally using the SINPO code)
   Section::::Ground loss.
  
  For monopole and other ground-based antennas, ground loss occurs due to ohmic resistance in the antenna's connection to its ground plane/counterpoise, including its mast or stalk and its bonding connections, as well as the ohmic resistance encountered by radio-frequency currents in the ground plane in the vicinity of the antenna.
  
  Section::::Aperture efficiency.
   BULLET::::- "Yagi-Uda" – One of the most common directional antennas at HF, VHF, and UHF frequencies. Consists of multiple half-wave dipole elements in a line, with a single driven element and multiple parasitic elements which serve to create a uni-directional or beam antenna. These typically have gains between 10–20 dBi depending on the number of elements used, and are very narrow band (with a usable bandwidth of only a few percent) though there are derivative designs which relax this limitation. Used for rooftop television antennas, point-to-point communication links, and long distance shortwave communication using skywave ("skip") reflection from the ionosphere.
   Section::::Antenna parameters.:Directivity.
   Minor components - CES (Complete Equipment Schedule):
  
  BULLET::::- 3 ft antenna - 'bush/battle whip'
  
  BULLET::::- 10 ft antenna
  
  BULLET::::- 3 ft antenna base - 'gooseneck'
  
  BULLET::::- 10 ft antenna base
  
  BULLET::::- Handset
  
  BULLET::::- Harness
  
  Section::::Users.
   BULLET::::- Off-center fed dipole antennas – also called “Windom” antennas – By carefully selecting the position of a feedpoint about of the way from the end of a half-wavelength wire, its feedpoint impedance is nearly constant for a variety of nearly-harmonic frequencies of the half-wave frequency. All Windom-style antennas have wide coverage gaps inbetween their nearly-harmonic working bands. Varying the position and length of the antenna, and adding loading stubs near its center can alter the sequence of feasible frequencies, and add more frequencies to the list. Among the off-center-fed designs are the “Carolina Windom”, which deliberately uses radiation from its feedline, K5GP antenna, ON4AA antenna (six bands).
   BULLET::::- Stage 1: formula_1 is equal to the loss of the cable and will increase with ambient temperature
  
  BULLET::::- Stage 2: formula_2 will depend on the lossiness of the cable. Since the element is lossy formula_2 is less than one; in order words, it will increase formula_13. The more loss, the closer formula_2 is to zero and the more formula_5 will increase.
  
  What can be done to improve the receiver to pick up very weak signals? It must have a lower noise figure; that is when the TMA comes into use.
  
  Section::::Applying the Friis formula to TMAs.:Typical receiver with TMA.
   BULLET::::- Bell Laboratories Layered Space-Time (BLAST), Gerard. J. Foschini (1996)
  
  BULLET::::- Per Antenna Rate Control (PARC), Varanasi, Guess (1998), Chung, Huang, Lozano (2001)
  
  BULLET::::- Selective Per Antenna Rate Control (SPARC), Ericsson (2004)
  
  BULLET::::- Some limitations
  
  BULLET::::- The physical antenna spacing is selected to be large; multiple wavelengths at the base station. The antenna separation at the receiver is heavily space-constrained in handsets, though advanced antenna design and algorithm techniques are under discussion. "Refer to: multi-user MIMO"
  
  Section::::Forms.:Multi-user types.
   The "low level analog front end (AFE) amplifier circuitry of receivers sensitive enough to detect signals at -130dBm levels and below are invariably extremely sensitive to high power levels. Typically, without the protection and isolation provided by T/R switches, the receiver AFE would be overwhelmed or destroyed by the normal transmitter power" levels which are in the +50dBm or more range. Consequently, receiver AFE antenna input terminals must be protected. With QSK operation this receiver protection is provided by well designed robust analog hardware T/R switches placed between the receiver AFE circuitry and the radio antenna.
  