Signal questions......

Dude111

Im kinda curious,if someone was 3048 Meters up on a mountain HOW FAR AWAY COULD THEY TALK TO SOMEONE WHO IS ALSO 3048 Meters on a mountain? (NO ACTIVE SKIP)

Say someone on the east was 3048 Meters on a mountain and someone far far away was 3048 Meters up,could they here each other seeing they are at the same elevation?

Now the lower the freq they are on the better chance obviously but regardless,at 3048 Meters I RECKON ANY FREQ CAN BE HEARD WAY FAR AWAY (@ the same elevation)

Just something i was curious of.......

watty

At say 50MHz the distance is MUCH more than 1200MHz.

If there is a mountain half way of correct height you can get you can get much more distance.

As the height increases you reach a point where the distance will hardly increase at all.

Also there is still inverse square law. double distance gives 1/4 power. So depends on power.

brownmini

Dude111 wrote: »

Im kinda curious,if someone was 3048 Meters
up on a mountain HOW FAR AWAY COULD THEY TALK TO SOMEONE WHO IS
ALSO 3048 Meters on a mountain? (NO ACTIVE SKIP)

Say someone on the east was 3048 Meters on a mountain and someone far
far away was 3048 Meters up,could they here each other seeing they are
at the same elevation?

Now the lower the freq they are on the better chance obviously but
regardless,at 3048 Meters I RECKON ANY FREQ CAN BE HEARD WAY FAR
AWAY (@ the same elevation)

The old formula for calculating distance (in miles) line of sight used to be
1.23 x SQUARE_ROOT( height_of_TX_in_feet + height_of_RX_in_feet)

Which gives a distance of 173 miles


However if you have a gawk at
http://www.qsl.net/kd4sai/distance.html

And type in your values in feet, this website seems to suggest that the
total range of two boyos sitting at 9999 feet is 282 miles with each of
them capable of reaching 141 miles by themselves.

There is more on Wkipedia at http://en.wikipedia.org/wiki/Radio_horizon

Remember this is theory, may not work in practice.
If you are going to give it a try and if you are going to try it in Ireland then
good luck in finding even one place that is over 5000 feet high never mind
2 at 9999 feet high and especially with no obstacles in the way at the mid
point.

watty

Any decent formula should have a frequency component. Most "radio horizon" calculators are copy of WWII radar calculation with empirical constant for a high UHF frequency, so too big a number for 10GHz and too small for 30MHz. Also doesn't take into account Fresnel effects or Ground wave on LF, MF, HF and low VHF

A mid point obstacle can increase range! (Diffraction).

always do "view source"
via http://www.qsl.net/w4sat/horizon.htm

<title>VHF/UHF Line of Sight Calculator</title>
<script language="JavaScript">
<!--
function calc(page) {
   mast1 = parseFloat(page.height1.value);
   mast2 = parseFloat(page.height2.value);
   if(page.units[1].checked) {
      mast1 = mast1/0.3048;
      mast2 = mast2/0.3048;
   }
   d1 = Math.sqrt(2*mast1);
   d2 = Math.sqrt(2*mast2);
   if(page.dist[1].checked) {
      d1 = parseFloat(d1*1.609);
      d2 = parseFloat(d2*1.609);
      unit = "   Km";
   }  else unit = "   Miles";
   d1 = Math.round(d1);
   d2 = Math.round(d2);
   page.horiz1.value = d1+unit;
   page.horiz2.value = d2+unit
   page.distance.value = Math.round(d1 + d2)+unit;
}
//-->
</script>
</head>

http://www.qsl.net/kd4sai/distance.html

<script language="JavaScript">
<!--
function calc(page) {
   mast1 = parseFloat(page.height1.value);
   mast2 = parseFloat(page.height2.value);
   if(page.units[1].checked) {
      mast1 = mast1/0.3048;
      mast2 = mast2/0.3048;
   }
   d1 = Math.sqrt(2*mast1);
   d2 = Math.sqrt(2*mast2);
   if(page.dist[1].checked) {
      d1 = parseFloat(d1*1.609);
      d2 = parseFloat(d2*1.609);
      unit = "   Km";
   }  else unit = "   Miles";
   d1 = Math.round(d1);
   d2 = Math.round(d2);
   page.horiz1.value = d1+unit;
   page.horiz2.value = d2+unit
   page.distance.value = Math.round(d1 + d2)+unit;
}
//-->
</script>

Both those are not much good. They both copied something older.
This is the same and equally poor http://radarproblems.com/calculators/horizon.htm

See here. Some allowance for Frequency. http://www.fcc.gov/mb/audio/bickel/curves.html
At lower HF frequencies you also get Groundwave. This is NOT the same as LOS communications. Even 28Mhz has some Groundwave.
198kHz has lots

See http://www.smeter.net/propagation/grndwav3.php For 20MHz

Distance to the radio horizon, approximately 80/Cube-root(MHz) Km, is where diffraction loss begins to take effect. Up to the horizon the Earth is assumed flat. Diffraction loss in dB increases in proportion to path length and to the cube-root of frequency. It is also affected by the type of terrain.

download Groundwave calculator (takes frequency into account) http://www.smeter.net/software/grndwav3.exe

brownmini

watty wrote: »

Any decent formula should have a frequency component. Most "radio horizon" calculators are copy of WWII radar ...

One must learn to walk before one considers to run.

Dude111

watty wrote:

198kHz has lots

Yes i reckon it does!! (Anything below .500Mhz has excellent coverage (With less power)