I have not read every communication about the radio and maybe someone has mentioned this. One other thing you want to make sure is that you have a strong 12V+ at the radio when the mike key is pressed in the 25 watt setting.
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Richard A Litton Sent: Wednesday, August 05, 2009 8:21 AM To: [email protected] Subject: [UnifliteWorld] Re: VHF Radio Great explanation! Thanks for taking the time. Rich and Vicky flitebuilder wrote: > 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 BlackBerryR 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 -~----------~----~----~----~------~----~------~--~---
