Question: Why Day And Night Frequency Is Different In HF Communication?

What is difference between HF and VHF?

VHF operates at a higher frequency range than HF, usually between 30-300 MHz.

These transmissions, due to their higher frequency, penetrate through the Ionosphere, with little or no refraction.

VHF propagation is ‘line of sight’ in nature and so is restricted to shorter-range communications..

What is the advantage of high frequency?

Smaller antennas require less material, are easier to mount, and are more discrete. Higher frequencies provide more bandwidth; you could send far more data in less time with a VHF antenna than a lower frequency antenna.

Which frequency band is used for long distance?

For radio frequencies, around 20 Meter/14 MHz is a workhorse (DX – Long distance) frequency range, and the 40 Meter/7–7.3 MHz band is also often the best for long distance communications.

How far can an AM radio signal travel?

about 100 milesUseful daytime AM service is generally limited to a radius of no more than about 100 miles (162 km), even for the most powerful stations. However, during nighttime hours the AM signals can travel over hundreds of miles by reflection from the ionosphere, a phenomenon called “skywave” propagation.

Why do we use high frequency in communication?

So high frequency carrier frequencies are used in RADIO transmission because space is an insulator and one can have electric current in it to magnetise it only if the source contains a RATE OF CHANGE OF VOLTAGE or a varying electric field.

Why does AM radio go further than FM?

Both AM and FM transmit a signal via electromagnetic waves. … AM radio provides a much stronger signal: the carrier wave on AM can travel for longer distances because it can adapt its direction to accommodate what is going on in the ionosphere.

Can VHF communicate with UHF?

It is not possible to match UHF and VHF frequencies, because UHF radios only communicate in UHF 430-470 MHZ range and VHF radios communicate in VHF 150-174 MHZ range.

Is HF line of sight?

HF (3-30 MHz) radio waves propagate either as line-of-sight (space) or sky waves. … Usually the straight line distance is limited by the horizon (the point where the straight line path is tangent to the earth).

Is VHF or UHF better?

In general, UHF radios are better for indoor use because their wavelengths are shorter and better able to penetrate through steel and concrete. … VHF radio signals tend to degrade more than UHF signals indoors.

What HF frequency is best?

A good rule of thumb for the time of day is that the higher frequencies are best during daylight (10 to 29.9999 MHz) and lower frequencies work best at night (2 to 10 Mhz).

What is a problem associated with very high frequency waves?

VHF waves, unlike longer waves, are not strongly reflected from the atmosphere; therefore, they do not bend readily around the Earth’s curvature and cannot be transmitted beyond the horizon. Their range is further limited by their inability to pass through hills or large structures.

Does higher frequency mean louder sound?

Finding out about frequency When a noise is made, it creates a vibration – the size of this vibration is called amplitude, and the speed of the vibration is called frequency. Larger vibrations means the sound is louder – called high amplitude – whereas high frequency refers to a higher pitch of sound.

Do radio waves travel farther at night?

Not all radio waves travel farther at night than during the day, but some, short and medium wave, which AM radio signals fall under, definitely can given the right conditions. … Without interference, radio waves travel in a straight line from the broadcast source, ultimately hitting the ionosphere.

Why is high frequency reception better at night?

It is called the ionosphere because when the sun’s rays hit this layer, many of the atoms there lose electrons and turn into ions. … You can pick up some radio stations better at night because the reflection characteristics of the ionosphere are better at night.

What is the range of HF?

High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred metres).