The 'fancy math' is actually a rule of thumb. it does not take into account the other ship's antenna. If the RX antenna is 100 + feet in the air then you could have a hand held radio in a dinghy 30 miles away and they would be able to hear you.
To use the term that VHF is line of sight is a little mis-leading. Line of sight usually referrs to radio apparatus that operate in the microwave and higher ranges. Examples are radar sets and satellite communication. VHF marine communication is very close to the old analog TV transmissions. it is affected by the weather tremendously. For instance, on a heavily overcast day you can expect to get at least twice the range from your radio. At night the range is also increased. To really figure out how far a transmission will go requires a lot of parameters. The rule of thumb is used as a tool in selecting an antenna and determining where to install it. It gives you a minimum transmit distance that you can expect. One rule that never changes in the world of radio communication is higher is better (unless you have a SSB and that is better left to a seperate thread). One other item that is constantly overlooked in a radio installation are the connections from the antenna to the radio. if these connections get any corrosion on them then you can expect NOT to hear remote stations or be able to transmit as far either. When looking at radio signals they are extremely small and and type of resistance between the antenna and the radio will greatly affect them. Thanks, Victor On Aug 4, 1:11 am, [email protected] wrote: > I do not know where the fancy math formula came from but I have talked from > my home slip to a person over thirty miles away several times. Standard > Horizon 16 ft. Eight foot extension ona eight foot antenna both from > Shakespere. > Jim > -------------- Original message from [email protected]: -------------- > > > > > Don't fuck around! When you need a ship radio you can't depend on a hand > > held! Don't pinch! Hand held is for use in a dingy or day trip. You want to > > take the boat out with > > people aboard? Equip with a ship radio. > > Not discussion. > > Sent from my BlackBerry® wireless device > > > -----Original Message----- > > From: waterguy > > > Date: Mon, 3 Aug 2009 19:02:02 > > To: UnifliteWorld > > Subject: [UnifliteWorld] Re: VHF Radio > > > Two things to keep in mind. First, VHF is line-of-sight; the radio > > waves don't follow the curvature of the earth. Your antenna must > > "see" the other antenna. This means, the higher the antenna, the > > greater the range. Generally speaking, the top of a mounted whip > > antenna for a fixed unit will be higher than the top of an antenna for > > a handheld. I think some handhelds have connectors to attach to an > > external antenna, but I don't know for sure. > > > Second, there's a significant performance difference: The maximum > > power output of a handheld is 6 watts. Maximum output of a stationary > > mount unit is 25 watts. Power and antenna height translate directly > > to range. Most handhelds aren't dependable for more than about 5 > > miles. Being that VHF is line-of-sight, the power issue is not such a > > big deal because you'll frequently lose contact because the other > > station goes over the horizon rather than losing the signal due to > > insufficient power. However, more power when the stations are just at > > the margin of losing contact due to going out of line of sight can > > make the difference between understanding and not understanding a > > message. > > > The formula for determining range is: (Square root of height of > > antenna above the water) x 1.42 = range in miles. > > > So if you're standing at your lower helm with a handheld, and the > > height of the antenna is 9 feet above the water, the range would be > > SQRT(9) x 1.42 > > 3 x 1.42 > > = 4.26 miles. > > > If you have an 8-foot antenna (most 6 dB antennas), mounted on a > > flybridge rail 15 feet above the water, the antenna height would be 23 > > feet, so the range would be > > SQRT(23) x 1.42 > > 4.795 x 1.42 > > =6.81 miles -- almost a 40% improvement in range. > > > If you have a 20-foot fixed antenna (most 9 dB antennas are between 18 > > and 23 feet) mounted on a rail 15 feet above the water (35 foot > > antenna height), range would be > > SQRT (35) x 1.42 > > 5.91 x 1.42 > > =8.4 miles - double the range of the handheld. > > > That's why I'd buy a handheld for use in the dinghy or in harbor, or > > with someone you know to be close, or if you have to ditch; but I'd > > always want to have a fixed mount unit with a good whip antenna, with > > a 9 dB gain and a 5/8 standing wave ratio (SWR) antenna. If I hit a > > log and start taking on water, I want my Mayday signal to blast the > > Coast Guard radio operator and everyone else around out of their seats.- > > Hide quoted text - > > - Show quoted text - --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/UnifliteWorld?hl=en -~----------~----~----~----~------~----~------~--~---
