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which signal covers the more distance HF or LF

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chandu.kurapati

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Hi all,

This discussion is too much confusing for me, please explain me which signal covers the more distance i.e low frequency or high frequency and please consider all factor to convey and explain me with good example.

Thanks & Regards

Chandu.Kurapati
 

A low frequency signal undergoes less attenuation per distance transmitted as compared to a high frequency signal.This is the reason why emergency service broadcasts are made at a frequency of 50KHz..because you want your message to go as far as possible..you might be in a forest with civilization very far away..and you need to get your emergency message across.If you are looking for more range...low frequency signal is preferred.
 

Um, kind of...

The problem with low frequencys is that for good radiation efficiency the aerials become absolutely massive.

50KHz would surprise me as a viable frequency for emergency comms, getting range beond a few tens of miles on the 73KHz ham band requires hundreds of watts into the typically electrically very short aerials used, and that is a frequency 50% higher then 50K.
The emergency beacons I am aware of are usually using a mixture of 121.5MHz (Aircraft emergency channel) and ~450MHz (To earth observation satelites, sending ID number and GPS location), both are high enough to be pretty much line of sight, but as the recevers are all overhead that works.
Emergency comms within a team of responders are usually VHF/UHF often trunked these days.

The old marine band back in the spark and Paulsen arc transmitter days was 500KHz and required fairly heroic matching networks to match a wire the length of a ship operating over water, power inputs were many Kw for transatlantic operations.

Moving up the frequency range to say 20M wavelengths ~14MHz, worldwide comms can be had with 100W or so into a dipole 10M long (Conditions depending), this works by reflecting the energy off the ionosphere so allowing over the horizon operation.

Up into the VHF and UHF, we are basically down to more or less line of sight, these signals do not (usually) reflect off the ionosphere (There are conditions where it happens but they are rare), the aerials are however sane sizes for a handheld set. Long distances can be covered either via the use of a repeater station on a high location, or via advanced tequniques like moon bounce, meteor scatter and satellite comms.

Moving further up into the microwave bands, very high gain aerials become practical, but the paths become pure line of sight, howerver getting large data rates becomes progressively easier at higher frequencies....

Nothing is simple, and frequency is always a tradeoff between many constraints (as is all engineering).

Regards, Dan.
 
Hi all,

This discussion is too much confusing for me, please explain me which signal covers the more distance i.e low frequency or high frequency and please consider all factor to convey and explain me with good example.

Thanks & Regards

Chandu.Kurapati
Let me give you one general example that we can observe that all vehicles use back lights in red color ,because red light will have large wavelength they are visible even at long distances.
similarly all Radio signals but they are not visible to human eye.
 

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