which will cover more distance: Low or high Freq. signal??

[rag_perfect]

hi friends...
can any body plz explain to me that which type of signal will cover more distance: Low frequency signal or high frequency signal?? and why so??

 

[rajanarender_suram]

high frequency will do., because higher the frequency farer they travel in dielectrics

 

[manish12]

Re: which will cover more distance: Low or high Freq. signal

i think it is depend on power.

and there is also a relation

p α f

more power , energy to travel larger distant

we say that

more freq >> more power >> more distant

 

[A.Anand Srinivasan]

high frequency signal travel longer... due to more power

 

[safwatonline]

longwaves follow the earth curvature while shortwaves are affected by the atmosphere and are refracted by the ionosphere so i think it is not an easy question and it depends on many parameters like place distance atmosphere and so on

 

[xtcx]

Re: which will cover more distance: Low or high Freq. signal

Low frequency and high frequency waves travel at the same speed, except for the fact, that the low freq carries less information per time when compared to high frequency.low frequency waves are much longer than high frequency waves. In fact both will travel long distance if the external parameters are considered nil\ideal. Because both are simply EM waves. They differ only in rate of information sent.Due to the penetration power of high frequency radio waves in general, is the major limitation of FM staions where the AM uses ionosphere for reflection and hence it covers more distance. In this scenario Low Frequency wins. But generally when you speak of sending information to some other medium with straight line of sight,high frequency wins, that means it can send more information within a given time than a low freq wave. No speed difference. Since it sends data faster, it's appeared that the wave as particle nature are slower. I guess it's a mis-belief.And in our theory, less frequency means less information per given time.Correct me if I'm wrong....

 

[safwatonline]

in AM waves the information is in the envelope so at a unit time the amount of information is the same whatever the carrier frequency

 

[xtcx]

Re: which will cover more distance: Low or high Freq. signal

in AM waves the information is in the envelope so at a unit time the amount of information is the same whatever the carrier frequency

yes!, but the AM carriers aren't supposed to reach frequencies of FM carriers. AM freq range for eg from 700KHz to 1500KHz where as FM ranges 86MHz to 109MHz approx. This standard is for radio broadcast, however the AM modulation freq is always lesser than FM.

 

[safwatonline]

it seems confusing to me,
lets say we have a PSK signal if i used the same signal with a carrier fc=1MHz this doesn't give any lower information than using the same signal with a carrier with fc=2MHz
as the information is in the signal and has nothing to do with the carrier

 

[amihomo]

Re: which will cover more distance: Low or high Freq. signal

In free space the relation between the transmitted power (Pt) and the recieved power (Pr) , is :

Pr ~ ( G/(f^2 × d ^ α )) × Pt

in which , G is the transmitter antenna gain ;
d is the distance between transmitter and the reciever ;
f is the carrier frequency ;
α is the path loss exponent;

from the above equation , we realize that the greater the frequency is , the less power will be recieved at the reciever , which means that high frequency signals can travel a smaller distance comparesd to lower frequncy signals.

That's why in GSM the 1800 Mhz band is used for small cells inside urban areas , while 900 MHz band is used for rural areas (larger cells) .

 

[xtcx]

Re: which will cover more distance: Low or high Freq. signal

it seems confusing to me,
lets say we have a PSK signal if i used the same signal with a carrier fc=1MHz this doesn't give any lower information than using the same signal with a carrier with fc=2MHz
as the information is in the signal and has nothing to do with the carrier

The carrier frequencies have nothing to do with the amount of information sent\received per given time. They help in carrying after all. It is the information signal which we send has the information. Need more info to be sent short in time?,use more bandwidth. Thats what they do.

 

[rag_perfect]

Re: which will cover more distance: Low or high Freq. signal

frnds.. thankx to all of u for giving me replies..
actually..
in modulation theroy my lecturer told that Baseband signal that is Low frequency signal that can not travel farther by itself so we are putting it over Carrier(high frequency signal) so that it can travel to longer distance.

Is it true that Baseband can not travel to longer distance by itself??

 

[the_risk_master]

Re: which will cover more distance: Low or high Freq. signal

Actually Lower frquencies travel farther than Higher Frequencies

if you take a look:

FSL = 96.6 + 20log(D) + 20log(f)

as frequency increases, free space attenuation does too (what more if it traverse air particles)

in LORAN systems too, (long-range navigation)
lower frquecies are used to extend the range of the system

the problem in baseband is the power (amplitude)
thats why we needed modulation at higher frequency carrier (high power as well)
to embed the baseband to carrier to combat noise at it travel the air medium

 

[behy]

Re: which will cover more distance: Low or high Freq. signal

of course there are some ambiguity in your question. what is your mean of high and low
each frequency band has especial transmission characteristics for example FM is not very high but because of its reflection from the atmosphier, it can pass very loge distances

 

[abbas_0612000]

Re: which will cover more distance: Low or high Freq. signal

High frequency attenuate more.

 

[rag_perfect]

Re: which will cover more distance: Low or high Freq. signal

If high frequeny attenuates more then that will be a disadvantage of modulation.but nowhere i have seen this fact??? plz help....

and frnds can anybody explain:
Is it true that Baseband can not travel to longer distance by itself??

 

[A.Anand Srinivasan]

by baseband they must have talked about speech signal... that is true due to low frequency...

 

[Element_115]

Re: which will cover more distance: Low or high Freq. signal

I think you are confusing different issues.

Base Band is the data/information to send, it is not conditioned for wireless
transmission.

As far as what Freq is best for long distance:

1) On earth communications it would be low freq's. Low Freq travel farther and
can bounce off the atmosphere. But low freqs can only send low data rates
(In general)

2) Off earth comm's they use ~ mid-freqs 1.7-2.2GHz this is so the signal can
leave the atmosphere (satellites).

3) For point to point they use higher freqs, Microwave. But this is for shorter distance
(Line of sight), Higher Freqs has their energy absorbed by the whether etc...
High Freqs can send higher data rates!

And you where also talking about modulation types. You can look at a chart that
shows the theoretical BER capability for different modulation type, it
shows what is the lowest Signal to Noise Ratio of each type that guarantees
certain a BER rate. I beleive that BPSK and PSK have the best performance.
See Dig Comm by B.Sklar

Cheers

 

[Naveed Alam]

Re: which will cover more distance: Low or high Freq. signal

If high frequeny attenuates more then that will be a disadvantage of modulation.but nowhere i have seen this fact??? plz help....
and frnds can anybody explain:
Is it true that Baseband can not travel to longer distance by itself??

if u do not modulate the baseband signal then just imagine ur antenna size. U will not be able to have a mobile phone in ur pocket.

the guy who gave explanation just above me, is good. It will clear rest of the questiones.


Naveed

 

[sayphong]

Re: which will cover more distance: Low or high Freq. signal

Hello,
high frequency travelles straight, does not follow the earth like light. low frequencies are reflexted by the ionosphere and travel around the earth. longwave was used to contact the ships anywhere on earth.
It depends if you are on earth or in space.
Sayphong