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<DIV><FONT color=#000000 size=2>Jack Carr sent this to me and I thought it might 
be interesting enough to pass on to you as you start getting those spring urges 
to get out on the water. Thanks Jack.</FONT></DIV>
<DIV><FONT color=#000000 size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2>Chuck Vande Wetering</FONT></DIV>
<DIV><FONT face=Arial size=2><B>-----Original Message-----</B><BR><B>From: 
</B>Jack Carr &lt;<A 
href="";></A>&gt;<BR><B>To: </B>Chuck Vande 
Wetering &lt;<A 
</B>Sunday, April 11, 1999 7:52 AM<BR><B>Subject: </B>Horizon (<A 
<DIV><FONT color=#000000 size=2>Hi Chuck. thought you might be 
<DIV><FONT color=#000000 size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2>Cheers</FONT></DIV>
<DIV><FONT size=2>Jack</FONT></DIV>
<DIV><FONT size=2></FONT>&nbsp;</DIV>
<CENTER><FONT color=green><FONT size=6><U><EM>The VHF/UHF Line of Sight 
Horizon</EM></U></FONT></FONT> </CENTER><BR>
<CENTER><FONT color=red>How High Determines How Far You, and Your Radio, Can 
See</FONT> </CENTER></H3>
<P>VHF and UHF radio propogation is often referred to as <EM>line of sight</EM>. 
There are many propogation modes that will vastly increase your range past line 
of sight distances, such as tropo ducting, tropo scatter and sporatic E, but 
clear line of sight is what you can always count on. </P>
<P>To give you an idea of what that is, here are a few examples. The actual 
radio horizon is usually a tiny bit further than the visual horizon, as much as 
15 percent at some frequencies. Height is everything. Not only the height of one 
antenna, but the height of the other. Each has its own horizon, and the line of 
sight between the two is the &quot;cohorizon&quot; or what distance the two 
horizons just touch. </P>

<P>So what is the mutual co-horizon of <B>two people on level</B> ground using 
HT's? Assuming an antenna height of six feet on each end and no intervening 
obstructions: </P>
<CENTER>Effective co-horizon is 6.9 miles </CENTER></H3>
<P>What happens if you mount <B>an outside antenna</B> on a single story house 
at the level of the eves, say about 14 feet up and talk to someone using an HT 
on the same level ground: </P>
<CENTER>Effective co-horizon is 8.7 miles </CENTER></H3>
<P>What happens if one person is on the <B>10th floor lanai</B> of a condo or 
has a fancy 100 foot tower: </P>
<CENTER>Effective co-horizon is 17.6 miles </CENTER></H3>
<P>How about someone on the top of <B>Mauna Kea</B> on the Big Island talking to 
an HT at sea level, such as a standing in a yacht offshore: </P>
<CENTER>Effective co-horizon is 169.7 miles </CENTER></H3>
<P>And finally, how about someone on <B>Mauna Kea</B> talking to someone on 
<B>Tantalus</B> on Oahu?: </P>
<CENTER>Effective co-horizon is 226.1 miles! </CENTER></H3>
<P>As you can see, when altitudes start being measured in thousands of feet, the 
horizon starts to really stretch outwards. This is the basis of &quot;mountain 
topping&quot;, the practice of taking VHF rigs to very high locations to see how 
distant a station you can work. </P>
<P>On the other hand, an outside antenna mounted on the eve of your single story 
house, is not going to improve your horizon that much over a handheld in your 
living room. BUT it is going to make a big difference in the efficiency of the 
radiation, being outside and mounted high and clear in an optimum place, above 
at least some of the surrounding vegetation etc. </P>
<P>Often condo dwellers can get remarkable VHF ranges by hanging up a roll up 
J-pole in an optimally exposed spot on their lanai. When their height above 
ground, which can be significant if they are on the 20th or 30th floor, is 
combined with height above sea level, which even in Honolulu can be several 
hundred feet, they end up with a rather impressive radio horizon. This can make 
such a location a surprisingly good VHF Simplex Net Control Station. </P>
<P>Take the case of a <B>20th floor lanai</B> on a condo that is up by H-1 on 
Oahu to our same person with a hand held at sea level: </P>
<CENTER>Effective co-horizon is 40.8 miles </CENTER></H3>

<P>In a recent VHF contest a station with a 25 watt mobile rig and a roll up 
ribbon J-Pole on a sixth floor lanai, worked both North and South sides of 
Kauai, Molokai, the Big Island and stations all over Oahu on both sides of the 
mountains. Maui stations were heard, but could not quite be worked. This was FM 
simplex operation with no repeaters. Most of the contacts were solid copy on 
only five watts. </P>
<P>VHF contacts from the same location in Moiliili were regularly made during a 
recent yacht race with boats in the Molokai Channel fully 15 miles from 
Diamondhead using 25 watts and a simple 5/8ths wave ground plane antenna. 
Contact was maintained all the way into the AlaWai Yacht Harbor except for a 
black out area when the boats were close under Diamondhead. </P><BR>
<P><A href="index.html">
<H3>Return to UH Ham Club Home Page</A></H3>01/98 


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