Frequency Types All Types of Frequency

[asimrsiddiqui 0]

EXTREMELY LOW-FREQUENCY

Extremely low frequency or ELF refers to the band of radio frequencies from 3 to 30Hz. The purpose of the EXTREMELY LOW-FREQUENCY (elf) communications system is to send short "phonetic letter spelled out" (PLSO) messages from operating authorities to submarines operating at normal mission speeds and depths. Elf has the ability to penetrate ocean depths to several hundred feet with little signal loss. This ability allows submarines to be operated well below the immediate surface and enhances submarine survivability by making detection more difficult.

 

Application

ELF is used by the US Navy to communicate with submerged submarines Despite the extremely high electrical conductivity of salt water, the water's density shields submarines from most electromagnetic communications. Signals in the ELF frequency range, however, can penetrate much more deeply. The low transmission rate of most ELF communications limits their use as communications channels; generally an ELF signal serves to request that a submarine surface and initiate some other form of contact.

 

Limitations

One of the difficulties posed when broadcasting in the ELF frequency range is antenna size. In order to transmit internationally using ELF frequencies, an extremely large antenna is required.

This is a one-way communications system from the operating authority to submarines at sea. The large size of elf transmitters and antennas makes elf transmission from submarines impractical.

 

VERY-LOW-FREQUENCY

Very low frequency or VLF refers to radio frequencies (RF) in the range of 3 to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals are used, such as for radionavigation. Because VLF can penetrate water to a depth of 20 metres (66 feet), they are used to communicate with submarines near the surface. (ELF is used for fully submerged vessels.)

VERY-LOW-FREQUENCY (vlf) transmissions provide a highly reliable path for communications in these northern latitudes as well as over and under all oceans and seas of the world.

 

Application

Vlf is currently used for communications to large numbers of satellites and as a backup to shortwave communications blacked out by nuclear activity.

Secondary applications of the vlf range include worldwide transmission of standard frequency and time signals. Standard frequency and time signals with high accuracy over long distances have become increasingly important in many fields of science. It is essential for tracking space vehicles, worldwide clock synchronization and oscillator calibration, international comparisons of atomic frequency standards, radio navigational aids, astronomy, national standardizing laboratories, and communications systems.

 

LOW-FREQUENCY

Low Frequency or Longwave radio frequencies are those below 500 kHz, which correspond to wavelengths longer than 600 meters. They have the property of following the curvature of the earth, making them ideal for continuous, continental communications. Unlike shortwave radio, longwave signals do not reflect nor refract using the ionosphere, so there are fewer phase-caused fadeouts.

The LOW-FREQUENCY (lf) band occupies only a very small part of the radio-frequency spectrum. This small band of frequencies has been used for communications since the advent of radio.

 

Application

In the past, the fleet broadcast system provided ships at sea with low-frequency communications via cw telegraph transmissions. As technology advanced, the system was converted to single-channel radio teletypewriter transmission. Today If communications is used to provide eight channels of frequency-division multiplex rtty traffic on each transmission of the fleet multichannel broadcast system

 

Limitations

Low-frequency transmitting installations are characterized by their large physical size and by their high construction and maintenance costs. Another disadvantage is low-frequency signal reception being seriously hampered by atmospheric noise, particularly at low geographical latitudes.

MEDIUM-FREQUENCY

Medium frequency or MF (sometimes called mediumwave) refers to radio frequencies (RF) in the range of 300-3000 kHz. The regular AM broadcast band is found in this range.

The MEDIUM-FREQUENCY (mf) band of the radio-frequency spectrum includes the international distress frequencies (500 kilohertz and approximately 484 kilohertz).

 

Applications

Mediumwave signals have the properties of following the curvature of the earth (the groundwave) and reflecting or refracting off the ionosphere at night (skywave). This makes this frequency ideal for both local and continent-wide service, depending on the time of day.

 

Limitations

Only the upper and lower ends of the mf band have naval use because of the commercial broadcast band (AM) extending from 535 to 1,605 kilohertz. Frequencies in the lower portion of the mf band (300 to 500 kilohertz) are used primarily for ground-wave transmission for moderately long distances over water and for moderate to short distances over land. Transmission in the upper mf band is generally limited to short-haul communications (400 miles or less).

 

SUPER HIGH FREQUENCY

Microwaves, also known as Super High Frequency (SHF) signals, have wavelengths approximately in the range of 30 cm (1 GHz) to 1 mm (300 GHz). However, the boundaries between far infrared light, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. The existence of electromagnetic waves, i.e. microwaves, was predicted by James Clerk Maxwell in 1864 from his famous Maxwell's equations. In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building apparatus to produce radio waves.

 

Application

The microwave spectrum is defined as electromagnetic energy ranging from approximately 300 MHz to 1000 GHz in frequency. Most common applications are within the 1 to 40 GHz range.

A microwave oven uses a magnetron microwave generator to produce microwaves at a frequency of approximately 2.4 GHz for the purpose of cooking food. Microwaves cook food by causing molecules of water and other compounds to vibrate. The vibration creates heat which warms the food. Since organic matter is made up primarily of water, food is easily cooked by this method.

Radar also uses microwave radiation to detect the range, speed, and other characteristics of remote objects.

 

 

 

VERY HIGH FREQUENCY

Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m).

VHF frequencies' propagation characteristics are ideal for short-distance terrestrial communication. Unlike high frequencies (HF), the ionosphere does not usually reflect VHF radio and thus transmissions are restricted to the local area (and can't interfere with transmissions thousands of kilometres away) It is also less affected by atmospheric noise and interference from electrical equipment than low frequencies. Whilst it is more easily blocked by land features than HF and lower frequencies, it is less bothered by buildings and other less substantial objects than higher frequencies. It was also easier to construct efficient transmitters, receivers, and antennas for it in the earlier days of radio. In most countries, the VHF spectrum is used for broadcast audio and television, as well as commercial two-way radios (such as that operated by taxis and police), marine two-way audio communications, and aircraft radios.

Application

Common uses for VHF are FM radio broadcast at 88-108 MHz and television broadcast (together with UHF). VHF is also commonly used for terrestrial navigation systems (VOR in particular) and aircraft communications.

EXTREMELY HIGH FREQUENCY

Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low (or far) infrared light. This band has a wavelength of one to ten millimeters, giving it the name millimeter band.

Limitations

Radio signals in this band are extremely prone to atmospheric attenuation, making them of very little use over long distances. Even over relatively short distances, rain fade is a serious problem, caused when absorption by rain reduces signal strength.

 

Application

This band is commonly used in radio astronomy.

 

 

 

ULTRA HIGH FREQUENCY (UHF)

Ultra high frequency (UHF) radio frequencies are those between 300 MHz and 3.0 GHz, which is higher than those of very high frequency (VHF). UHF and VHF are the most common frequency bands for television.

UHF frequencies have higher attenuation from atmospheric moisture and benefit less from 'bounce', or the reflection of signals off the ionosphere back to earth, when compared to VHF frequencies. The frequencies of 300-3000 MHz are always at least an order of magnitude above the MUF (Maximum Usable Frequency). The MUF for most of the earth is generally between 25-35 MHz. Higher frequencies also benefit less from ground mode transmission.

 

Limitations

However, the short wavelengths of UHF frequencies allow compact receiving antennas with narrow elements; many people consider them less ugly than VHF-receiving models

HIGH FREQUENCY

High frequency (HF) radio frequencies are between 3 and 30 MHz. This range is often called shortwave.

Since the ionosphere often refracts HF radio waves quite well, this range is extensively used for medium and long range terrestrial radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:

• Sunlight/darkness at site of transmission and reception

• Transmitter/receiver proximity to terminator

• Season

• Sunspot cycle

• Solar activity

• Polar aurora

• Maximum usable frequency

• Lowest usable frequency

• Frequency of operation within the HF range

 

Applications

HF is often used for continuous wave mores code transmissions.

[iGuest 3]

IF Frequency?,and RF Frequency ? the difference ?Frequency Types

I need some information of Radio FM and Radio SW. 

-reply by abdo abdel regal

 

[bobbybeeelan 0]

HiI think you're talking about AM And FM if so AM is good for carring long distance and FM is good if you want a channel to be goodByeP.S. Hope this helps

[iGuest 3]

AM transmission uses a specific (center) carrier frequency, and the receiver is tuned to that exact frequency. The bulk of the energy used supports this carrier frequency, and it is transmitted constantly, even if no audio is present. The audio portion is mirrored and each identical, reversed half surrounds the carrier at slightly lower and higher frequencies. Low notes and high notes 'wobble' around the solid center carrier frequency (thus Amplitude Modulation). There must be a minimum distance between each channel or their audio information streams would interfere with each other. You'll notice that some internationally-sold receivers may have a 9kHz/10kHz switch. Different countries have chosen to permit different spacing between channels. This limits the frequency range / fidelity of music but permits more usable AM channels in 9kHz countries. Since human voice varies from about 1 kHz to 3 kHz, there's plenty of room for vocal audio, but music is limited to about 10 kHz (music typically uses a range of about 0.2 kHz to 15 kHz, or 200 Hz to 15,000 Hz). The AM Broadcast Band is usually assigned to a range of 560 kHz (0.56 mHz) to 1605 kHz (1.605 mHz), but AM mode transmissions can occur over a much wider range of transmitted frequencies. AM is a simple wave; thus a basic crystal radio receives AM signals.

FM transmission 'wobbles' the carrier frequency up and down, according to the audio content (thus Frequency Modulation) and so requires sophisticated circuitry. Low notes transmit at a lower frequency on the dial than do high notes, so FM receivers must capture a slightly wider channel than what's shown on the dial. The FM Broadcast Band is often 88 mHz to 108 mHz, though some countries move it slightly. In those cases, a switch may be found on the receiver to choose the allocation of the FM Broadcast Band.

FM transmission can be used only at frequencies that support its bandwidth needs, but occasionally, the AM and FM systems leapfrog on the dial. For example, a commercial radio station at 1000 kHz (WCFL in Chicago) transmits in AM mode in the middle of the AM Band, a shortwave radio operator may use AM mode at 30 mHz and FM at 52 mHz for improved clarity, a television station will use FM for their audio content at 56 mHz, a commercial radio station at 107 mHz also broadcasts in FM mode, while an aircraft radio at 122 mHz operates in AM mode, largely for convenience and backward compatibility. Two AM transmitters on the same frequency will "heterodyne" or squeal, making both largely unintelligible as their carrier waves interfere. Two FM transmitters on the same frequency will merely sound confusing, like two people talking at the same time.

Spread-Spectrum radio varies the frequency used very widely, making jamming difficult or impossible, and can even make reception impossible without knowing how the frequencies will be varied. They are used by the military, but are finding their way into consumer products due to their ability to ignore interference. The concept was first patented by Hollywood actress Hedy Lamar during WWII (mid-1940's) using player piano rolls to quickly, predictably switch the channels used by torpedoes in their search for their target so they could not be jammed by the enemy. The technology was impractical at the time, but finally found use 10 or 20 years later and is in wide use today.  Multiple stations can use spread-spectrum in the same range, and experience no interference, since each follows a prescribed pattern, bouncing from one channel to another in very rapid succession. This also means atmospheric interference and enemy jamming are ignored.

Another mode not mentioned is sideband. All sideband methods are similar to AM mode, but gain greater distance by substituting some of the energy allotted for the audio portion to the carrier portion of the signal. Single Sideband strips one-half of the audio wave (which is actually a mirror of the remaining section) and uses the available energy to boost the carrier wave. Additionally, the carrier may completely disappear when no audio is present, thus saving additional energy. A special circuit, called a Beat Frequency Oscillator or BFO must be adjusted on the receiver to replace the missing sideband portion. If the lower portion is removed, then the transmitted signal uses only the Upper Sideband or USB. If the lower portion is used, the signal is Lower Sideband, or LSB. In theory, two different stations could transmit on the same carrier channel with limited interference, since much of the time, their carriers would be 'off' while no audio was present and their audio portions would be found in a different place, thus doubling available frequency allocations. Since the available energy is distributed differently, SSB radios are typically granted twice the legal limit for power output, permitting even greater distance (amateur radio operators are typically granted a maximum of 1,000 watts of final output power before the final RF stage in AM mode, so slightly less is presented to the base of the antenna, yet 2,000 watts SSB is permitted, and each watt travels farther). SSB is the choice for achieving the greatest range between transmitter and receiver, but requires mild discipline to tune the BFO correctly. SSB signals received without a BFO are garbled and cannot be understood, since only half (one side of) the original audio wave is present.

Double Sideband transmits both mirrored audio halves of an AM signal, so no BFO is required, simplifying reception. It still varies the carrier signal strength with the volume of the audio channel, so it can also dramatically vary the power used, and thus achieve greater distance. In other words, much more of the transmitted signal is devoted to the valuable audio signal, and far less to the relatively unimportant carrier wave.

An AM signal heard on a receiver that has a Signal Strength (SS) Meter will display a specific meter reading created by the carrier wave. The actual reading is based on distance, power, both antennas, receiver sensitivity, etc. This reading is ambiguous; a nearby, weak station can give the same SS reading as a distant, powerful station, and another, more sensitive receiver can give a higher SS reading using the same antenna. Using a different antenna can change the reading; SS is merely a relative comparison used to compare changes in equipment. A broadcast transmitted by DSB will bounce the meter down to zero when the audio is silent, reach the same height or higher as the AM reading when the transmitted audio is at maximum, and bounce between the two during normal speech or music. Since the overwhelming bulk of a transmitter's power is used to develop the carrier wave, moving energy from the carrier to the audio portion of the wave in DSB results in greater distance using the same average transmitted power.

Finally, sub-carrier FM transmissions are an inexpensive way to piggy-back an audio signal alongside a commercial FM-band transmission. Instead of shifting the carrier signal slightly as an FM radio, sub-carrier shifts a second audio signal dramatically to a distant area. This requires a special receiver or adapter since the audio portion is radically displaced from the carrier signal. It offers an inexpensive way to provide a second content channel using the same range as the FM station without interfering with the FM broadcast. They have been used by Public Radio stations to read to the blind. In this way, a blind person who lives near a commercial FM station can hear a special signal, perhaps the entire daily newspaper being read by volunteers, right down to the ads and sales events. Books, recordings and other content are popular, too.

-reply by Charlie Gosh

 

[iGuest 3]

IF / RFFrequency Types

IF stands for Intermediate Frequency. Modern receivers use IF to remove background noise and interference. The original received channel is 'bumped' to a second frequency by the amount of the IF, then both are compared. These two channels are combined and provide signal to later stages in the radio, so any noise that spreads across the entire radio band is ignored.

Early radios used Regenerative coupling to accomplish much the same effect, but they required the operator to manually adjust a 'Regen' control to tune the receiver properly. The invention of IF stages removed this control and made AM radios simple to tune.

So, if you tune an AM radio to 1000 kHz, the radio will actually generate a small second signal at1455 kHz (1000 plus 455). If you place a second AM radio nearby tuned to 1455 you can hear this as interference or a quiet zone. Tuning the second radio to an AM station, then sweeping the first radio up and down the dial will cause a heterodyne interference squeal to the radio station. The IF circuit listens to everything common to both channels, while ignoring everything else.

FM radios typically use a 10.7 mHz IF, so a radio tuned to 90 mHz will generate a small signal at 100.7 mHz. Some use a negative IF, so the second generated signal could be at 79.3 mHz (90 minus 10.7). Citizens Band operators used to modify (any modifications to a CB radio were illegal) specific radios by switching a transmit crystal to a receive socket to permit them to listen to Civil Air Patrol transmissions (but not transmit), as they were slightly below the CB band. The crystal was set to a frequency 455 kHz away from the actual channel. Later, the crystal arrangement was changed (combinations of much lower frequencies were added together) and this could no longer be done.

Some radios use non-standard IF frequencies for odd purposes, but they are rare. Nearly all consumer radio receivers use the IF method. There is no need for an IF stage in a transmitter.

RF is simply Radio Frequency. Any radio or television transmission is considered an RF signal. Microwaves signals are often called RF, but they are, in many ways, substantively different from radio waves. Moving up the spectrum, we find radio waves, microwaves, infrared (heat) waves, then visible light (red, orange, yellow, green, blue, indigo, violet), ultraviolet waves, far ultraviolet, and finally radiation-type waves (gamma rays, X-ray, cosmic rays, etc.).

Wavelengths below light are considered harmless (non-ionizing) while those above light are considered damaging (ionizing). That's the reason enough UV from sunlight damages skin, and enough X-rays damage tissue. Unfortunately, this old, simple distinction does not take into consideration the resonant frequency of any RF wave. If you carry a length of pipe on your shoulder as you walk, you will discover a specific pace that will bounce the pipe to match your stride. Any other pace will mismatch and repeatedly bang the center of the pipe into your shoulder. The matching pace is the pipe's resonant frequency. RF waves can match molecules and other objects, much the same way a specific musical note can match the resonant frequency of a wine glass and shatter it, or soldiers marching in unison across a bridge can destroy it (soldiers always break their march and walk normally). Two musical instruments can almost match notes and you'll hear a third 'beat' wave. When they match, they sound twice as loud. Microwave ovens rely on matching the exact resonant frequency of water molecules to excite and cause them to rub against each other, creating friction and heat.

Whether non-ionizing radio waves can cause similar interference and destruction of living body tissue remains to be seen, but it is an obvious physical principle. I wouldn't really care to live near a 50,000 Watt television transmitter. There is some research that suggests that the 60 Hz signal emitted by common telephone pole-mounted AC power transformers can be harmful, especially if a child spends every night near it for years. Cellphone transmitters are too new and too variable to be certain. Solid working knowledge of resonant frequency is critical in radio transmitter installations, and sometimes there are some surprises. Radio waves are funny stuff.

You'll sometimes notice radio frequencies listed in megahertz or meters (30 mHz equals 10 meters, while 300 mHz equals 1 meter). The mHz number is the number of times per second the wave of the radio signal oscillates, or changes direction. The meter number is the length between each wave. So, higher oscillations means shorter distance between each one. The meter number is the resonant frequency of the wave. Ideally, a 30 mHz transmitter or receiver would be matched to an antenna 10 meters (400 inches) at resonant length, or 800 inches (double-wave), or 250 inches (5/8 wave), or 200 inches (half-wave), or 100 inches (quarter-wave), or 50 inches (eighth-wave), etc. So, and old car with an AM radio needs a long antenna (1000 kHz at 1/100-wave is 30 inches), while a modern car with an FM radio uses a shorter antenna (100 mHz at 1/10-wave is only 15 inches). Antennas can be matched a multiple of the resonant frequency, so an antenna half as long is still useful, but won't capture or transmit as much signal strength. A small coil or other circuit is used to fine-tune to an exact frequency, if desired. Old AM car radios had a tiny screwdriver adjustment hidden underneath the tuning knob to final match the antenna to the middle of the AM band and account for cable, connectors, etc.; everything else was 'close enough.' The antenna on your computer's wireless router, operating in the same range as a microwave oven, is even shorter. Your cellphone's quarter-wave antenna can be so short it's placed inside the case. The low frequencies used decades ago on ships and aircraft meant a long wire antenna that stretched nearly the length of the ship or aircraft. Advancing technology meant higher frequencies could be used, and thus shorter antennas. A quarter-wave antenna at microwave frequencies would be very short.

Another phenomenon of RF energy and resonant frequency is an RF burn. Under certain conditions, an RF wave's resonant frequency can match the gap (or some multiple of it) between two objects (say, your hand and a transmitter antenna). The RF signal can unexpectedly be rectified by this gap and can instantly cause a very serious burn to tissue deep below the skin that can take months to heal, yet may leave the surface of the skin untouched. This is the (misguided) reason that cellphone users were once directed not to use their phone when pumping gasoline. The odds of the tiny transmitter in cellphones (on the order of 0.003 to 0.3 Watts in modern cellphones) creating an energy discharge border on the impossible. Technically? Yes. In reality? No. Key the microphone on your 200 Watt mobile amateur rig while pumping gas? Not a good plan.

An RF Stage is the last RF amplifier found in a transmitter before the signal is sent to the antenna. There is some loss in this stage. A transmitter rated at 5 Watts means that the manufacturer can deliver a 5 Watt signal to the final RF stage. The loss depends on the efficiency of the final RF stage, so the actual power delivered to the antenna may be only 4 Watts. Some regulations may specify 5 Watts max to final RF, 4 Watts max permitted to the antenna. If the final RF stage is cheap, poorly designed, or poorly adjusted, the actual output will be even less.

-reply by Charlie Gosh

 

[iGuest 3]

FM / AM distanceFrequency Types

AM and FM signals are generally lost over the horizon.  This makes FM signals perfect for local communications. There's no reason for Chicago police radio traffic to be heard in Dallas, or a Miami radio station playing ads to an audience in Boise. Since they don't interfere with each other, they can both use the same channels, minimizing the need for frequency space. FM Broadcast Band radio stations generally fade at about 50 miles on flat land, but if you're on a high hill, you can get considerably more distance.

AM signals can sometimes be heard thousands of miles away. This is caused by a phenomenon called 'skip' and is caused by a layer high in the atmosphere (the ionosphere) that causes the radio signal to reflect back to Earth. The reflected signal can then bounce off the Earth, then again off the skip layer, and continue around the globe. These signals often fade in and out as the skip layer shifts.

This generally occurs only at night, but there are exceptions. Solar activity scrambles the layers during daylight. At night, they layers of the ionosphere settle down and stratify into distinct zones. In the same way that still water becomes a mirror because of the difference in density between the air and the water, or the way a mirage appears in the desert, the layers act as a mirror to certain waves. Waves that are too long or too short pass right through these layers and escape to space.

Sunspots can increase this effect when their energy bursts 'charge' the ionosphere layers. Since sunspots have a natural 11-year cycle, distant radio stations may be available one year, then disappear the next, only to return 11 years in the future. The Aurora Borealis, or Northern Lights are also related to sunspot activity charging particles in the upper atmosphere (there is a similar activity over the South Pole).

So, on a clear summer night you may hear AM radio stations from very distant cities, but they disappear during the day. For this reason, AM stations typically have multiple antenna arrays that enable them to shape the direction of their signal. Government regulators tell them where they can direct their signal at night so they don't inadvertently interfere with other stations far away, then permit a different pattern during daylight hours.

Decades ago, ships at sea used on skip for radio communications. The low frequencies used then were even better than AM Broadcast Band channels for this purpose, though their lower frequencies also tend to follow the curvature of the Earth better than higher frequencies.

In the 1960's, Wolfman Jack got his start on Mexican AM radio station XERB which beamed its five-times-U.S.-standard powerful nighttime signal directly northward into southern California, giving him an enormous audience.

-reply by Charlie Gosh

 

[iGuest 3]

Typo - correctionFrequency Types

Typo: "Single Sideband strips one-half of the audio wave (which is actually a mirror of the remaining section) and uses the available energy to boost the carrier wave."

should read, "SSB strips much of the energy used for the carrier portion of the wave and puts it to use on the audio portion.  This makes the audio portion of the signal much stronger, enabling greater distance than a simple AM signal. Additionally, since the carrier is practically eliminated during silent moments, the operator benefits from averaging the total output over time. This enables an even stronger signal to legally be broadcast, since the "average" includes silent, low-power periods mixed with high-power audio passages.  Therefore, a 1,000 watt AM license permits 2,000 watts using single-sideband, and the signal itself penetrates even further because more power is diverted to audio rather than the non-informational carrier portion. Double sideband does not require a BFO at the receiver, but still benefits from transferring energy from the carrier to the audio sidebands to increase distance. You can tell a DSB signal on a signal-strength meter (S-meter) as the needle bounces up and down as the audio volume goes up and down. An AM signal has a steady S-meter reading. An SSB signal also bounces the S-meter, travels the furthest of the three modes, but requires a BFO to make the audio intelligible."

Also, FM sub-carrier transmissions have been used to carry instant information on traffic updates, severe weather, sports scores, stock prices, and other commercial ventures that would otherwise require tremendous capital expenditures, equipment and licensing to get the information to any users that have access to an ordinary commercial FM radio station.

-reply by Charlie Gosh

[iGuest 3]

Frequency requirement for the transmitter to a receiver in wireless microphoneFrequency Types

Hi,

I like to verify or get some info with regard to the transmitter and receiver of a wireless microphone as follows:

1. The required frequency have to be exact for proper function of the transmitter and receiver is this correct? say both have to exact in 171.9 mhz frequency.

2. In the commercial application of a transmitter or receiver (wireless microphone) frequency can be adjusted for it to match and function properly. Is this correct?

3. Commercial wireless microphone design frequency could vary so it is not interchangeable. But if two different mfg transmitter and receiver have the exact frequency then it should work - yes?

Thanks in advance for your reply

 -reply by John Wei

[iGuest 3]

ELF propertiesFrequency Types

Hi,

The extremely high frequencies are prone to atmospheric attenuation, and absorbtion, like rainfade.

In a similar way, the ELF, "extremely low frequencies" should be prone to some kind of attenuation, reflection, deflection, absorbtion or something equivalent of rainfading.

Does anybody know what attenuates or fades the ELF, "extremely low frequency" in the range of 3 to 30 hertz ?

Kind Regards.

-question by Ozgur