Band help

[biferi]

I know that Ground Wave or Serface Waves are VLF and LFF Bands.

What Bands are Line Of Site or Direct Wave???

 

[park]

I know that Ground Wave or Serface Waves are VLF and LFF Bands.

What Bands are Line Of Site or Direct Wave???

"they" say 2 meters and up are line of site. But from my own experience 800 mhz and above are in fact line of site.

 

[Chernobyl2]

I thought VHF and upwards was LOS?

FM radio at 100 MHz or so can be lost quite easily if there are obstructions.

http://en.wikipedia.org/wiki/Line-of-sight_propagation

Chernobyl2.

 

[biferi]

Thanks But??

So Line Of Site would be
VHF UHF and what other Bands??

 

[Beetle]

So Line Of Site would be
VHF UHF and what other Bands??

Any other band that doesn't have propagation beyond the RF horizon at the time.

 

[Robb]

If the question is 'at what frequency is line of sight propagation becomes an issue'? Then; I would say somewhere in between 6 meters and 2 meters - closer to 2 meters. After that - 440mhz is really 'iffy'. IF you have enough power and IF your antenna is in the right place - it will work.

My limited experience thus far...

 

[biferi]

Thanks again but?

So anything but HF is Line Of Site right??

 

[Chernobyl2]

If we are talking theoretically, VHF and above is, yes.

Practically, up to about 300 MHz can be received quite a distance from the source, but it depends on the landscape/obstructions between you and it, and its transmit power.

Assuming the ground followed the curvature of the earth, there is a cut-off at which the signal can no longer be received. This is the "horizon" with respect to the signal. Beyond this horizon, you are not "line of sight" with the transmitter, so to receive anything beyond this point requires one or more of the following:

* Reflection (ionosphere, buildings)
* Refraction (ionosphere. All signals refract slightly around the curvature of the earth, but those that refract sufficiently to enable you to receive a transmission, say, 100 miles away don't class as LoS).
* The charateristics of the signal created by the aerial.

If the signals don't do the above to a great extent (and this is true with higher frequencies) you need to be able to see the transmitter to receive.

Great examples of LoS:

* GPS (doesn't work indoors generally, and is sketchy at best through trees) - ~1.3 GHz

* Mobile telephones - 800 MHz to ~2.2 GHz

http://en.wikipedia.org/wiki/Ionosphere

Chernobyl2.

 

[Robb]

So anything but HF is Line Of Site right??

Well, up to 6 meters can produce 'skip' when conditions are there. But VHF and UHF is line of sight - a built-in limitation due to the way that it propagates. Some guys use satellites to bounce 2m and 440mhz. When you get closer to 1ghz; it is very directional and easily blocked. Just like a cell phone!

 

[Beetle]

Well, up to 6 meters can produce 'skip' when conditions are there. But VHF and UHF is line of sight - a built-in limitation due to the way that it propagates. Some guys use satellites to bounce 2m and 440mhz. When you get closer to 1ghz; it is very directional and easily blocked. Just like a cell phone!

Two meters will do that just as much as six meters given the proper conditions. Tropospheric ducting/sporadic "E" - call it what you will. Sometimes a band that's supposed to be LOS only will surprise you big time. Probability decreases inversely as frequency, however.