Home |
Search |
Today's Posts |
#31
|
|||
|
|||
Antenna for Marine VHF
On 4/23/2017 8:17 PM, Jeff Liebermann wrote:
On Sun, 23 Apr 2017 20:34:31 +0100, highlandham wrote: It is useful to initially make the vertical radiator and radials ,say 10 mm longer than a quarter wave for the mid band frequency (somewhere between 157 and 162 MHz). Nope. You want to tune the antenna for lowest VSWR in the transmit range (156.0 to 157.5MHz) and take whatever you can get in the 162MHz receive only region. If you try to tune the antenna for the middle of the 6 MHz split, you'll end up with lousy VSWR at both extremes where you want to operate, and good VSWR where you're not operating. Frank , GM0CSZ / KN6WH in IO87AT How lousy? Enough for the transmitter to reduce power to protect itself? Do you have SWR numbers? |
#32
|
|||
|
|||
Antenna for Marine VHF
On Sun, 23 Apr 2017 23:06:37 -0500, John S
wrote: On 4/23/2017 8:17 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 20:34:31 +0100, highlandham wrote: It is useful to initially make the vertical radiator and radials ,say 10 mm longer than a quarter wave for the mid band frequency (somewhere between 157 and 162 MHz). Nope. You want to tune the antenna for lowest VSWR in the transmit range (156.0 to 157.5MHz) and take whatever you can get in the 162MHz receive only region. If you try to tune the antenna for the middle of the 6 MHz split, you'll end up with lousy VSWR at both extremes where you want to operate, and good VSWR where you're not operating. Frank , GM0CSZ / KN6WH in IO87AT How lousy? Enough for the transmitter to reduce power to protect itself? Do you have SWR numbers? Of course I have numbers. I never go anywhere without a handy NEC model of a marine VHF band ground plane. For your viewing pleasu http://www.11junk.com/jeffl/antennas/Marine%20VHF%20Ground%20Plane/index.html If you want to play with it, the 4NEC2 model is at: http://www.11junk.com/jeffl/antennas/Marine%20VHF%20Ground%20Plane/slides/Marine%20VHF%20Gnd%20Plane.html Argh, you're right. With a Ground Plane, the VSWR is low enough at the band edges (156 - 163MHz) for transmit, if I tune the antenna for mid-band (159MHz). TX reverse power protection usual kicks in at 2:1. Looks like the VSWR at 156 and 162 is about 1.2:1 which is quite safe: http://www.11junk.com/jeffl/antennas/Marine%20VHF%20Ground%20Plane/slides/VSWR.html Lame Excuse: I'm used to dealing with higher gain marine band antennas, where the bandwidth is much less. With these antennas, it's common practice to tune the antenna for the transmit range, and take whatever you can get at the higher receive only frequencies. However, it seems the bandwidth of a common ground plane is sufficiently wide to have low VSWR over the entire VHF marine band. Grumble... -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#33
|
|||
|
|||
Antenna for Marine VHF
On Sun, 23 Apr 2017, highlandham wrote:
On 23/04/17 04:03, Jeff Liebermann wrote: quote ===== When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. unquote ===== A simple alternative to the J-Pole antenna would be a ground plane antenna made of welding rod material on an SO-239 socket with a 4 hole square flange with a vertical quarter wave radiator and 4 hinged radial elements,the latter under 45 degrees when in use . The SO-239 socket would be connected to a PL-259 connector and a suitable length of coax. But on a kayak? It won't do much good lying on the kayak, and unless you get it high enough (which has problems in itself), you'll poke your eye out. Why not go for something that doesn't need horizontal radials. Michael |
#34
|
|||
|
|||
Antenna for Marine VHF
On Sun, 23 Apr 2017, rickman wrote:
On 4/23/2017 4:26 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote: I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. I believe the issue of salt water came up because of a materials concern, aluminum vs. stainless steel. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. Not sure who told you about "push poles", but I've never run into kayaker with a push pole. If you get on rocks, you have a paddle. I don't even know where you would stow a push ploe. Much better to not get on the rocks. YOu have the length of the kayak. A bamboo pole is light, and making an antenna out of wire won't burden the pole. The real issue, I'd say, is figuring out something to put on the kayak to hold the pole. For emergencies, you can probably just have some fishing line tied to the top of the pole, and hold that as a "guy wire". If there was some way to hold the oar against the kayak, some clip on antenna that used the oar as a mast would be better than nothing, and of course doesn't require an extra pole. A bit of height probably does make an improvement, after that the "mast" has to get higher and higher to be useful. Michael |
#35
|
|||
|
|||
Antenna for Marine VHF
On 4/24/2017 3:44 PM, Michael Black wrote:
On Sun, 23 Apr 2017, rickman wrote: On 4/23/2017 4:26 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote: I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. I believe the issue of salt water came up because of a materials concern, aluminum vs. stainless steel. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. Not sure who told you about "push poles", but I've never run into kayaker with a push pole. If you get on rocks, you have a paddle. I don't even know where you would stow a push ploe. Much better to not get on the rocks. YOu have the length of the kayak. A bamboo pole is light, and making an antenna out of wire won't burden the pole. The real issue, I'd say, is figuring out something to put on the kayak to hold the pole. For emergencies, you can probably just have some fishing line tied to the top of the pole, and hold that as a "guy wire". If there was some way to hold the oar against the kayak, some clip on antenna that used the oar as a mast would be better than nothing, and of course doesn't require an extra pole. A bit of height probably does make an improvement, after that the "mast" has to get higher and higher to be useful. Bamboo poles are not all that light and they get water logged. Everything on a kayak gets wet. So far I haven't found anything definitive that even shows a better antenna is needed. It would appear if you are trying to contact a station with a high antenna some 20 miles away you might have trouble with range, but the problem isn't that your antenna isn't high enough. Reaching other handheld units is limited by line of sight which would be helped by a higher antenna. I'm not sure which problem was being addressed. Next time I talk to my buddy I'll ask more about this. I think in reality this was prompted by someone recommending a home brew antenna when the nature of the problem wasn't even explored. -- Rick C |
#36
|
|||
|
|||
Antenna for Marine VHF
On 4/24/2017 3:39 PM, Michael Black wrote:
On Sun, 23 Apr 2017, highlandham wrote: On 23/04/17 04:03, Jeff Liebermann wrote: quote ===== When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. unquote ===== A simple alternative to the J-Pole antenna would be a ground plane antenna made of welding rod material on an SO-239 socket with a 4 hole square flange with a vertical quarter wave radiator and 4 hinged radial elements,the latter under 45 degrees when in use . The SO-239 socket would be connected to a PL-259 connector and a suitable length of coax. But on a kayak? It won't do much good lying on the kayak, and unless you get it high enough (which has problems in itself), you'll poke your eye out. Why not go for something that doesn't need horizontal radials. Actually I gave this antenna some thought. If the radials were attached by some sort of hinge for example a heavy braid, they could fold up while still being electrically attached. The antenna could slide into a tube when not in use. It might be a bit complex to rig up, but this is the sort of thing I can give some thought to and maybe come up with something workable. -- Rick C |
#37
|
|||
|
|||
Antenna for Marine VHF
In article , rickman
wrote: On 4/24/2017 3:39 PM, Michael Black wrote: On Sun, 23 Apr 2017, highlandham wrote: On 23/04/17 04:03, Jeff Liebermann wrote: quote ===== When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. unquote ===== A simple alternative to the J-Pole antenna would be a ground plane antenna made of welding rod material on an SO-239 socket with a 4 hole square flange with a vertical quarter wave radiator and 4 hinged radial elements,the latter under 45 degrees when in use . The SO-239 socket would be connected to a PL-259 connector and a suitable length of coax. But on a kayak? It won't do much good lying on the kayak, and unless you get it high enough (which has problems in itself), you'll poke your eye out. Why not go for something that doesn't need horizontal radials. Actually I gave this antenna some thought. If the radials were attached by some sort of hinge for example a heavy braid, they could fold up while still being electrically attached. The antenna could slide into a tube when not in use. It might be a bit complex to rig up, but this is the sort of thing I can give some thought to and maybe come up with something workable. Back to the J-Pole! You can make a light, flexible J-Pole out of 300 Ohm twinlead. Feed it with RG-174 cable. Use some kind of oar or pole to raise it when needed. Fred |
#38
|
|||
|
|||
Antenna for Marine VHF
On Mon, 24 Apr 2017, rickman wrote:
On 4/24/2017 3:44 PM, Michael Black wrote: On Sun, 23 Apr 2017, rickman wrote: On 4/23/2017 4:26 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote: I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. I believe the issue of salt water came up because of a materials concern, aluminum vs. stainless steel. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. Not sure who told you about "push poles", but I've never run into kayaker with a push pole. If you get on rocks, you have a paddle. I don't even know where you would stow a push ploe. Much better to not get on the rocks. YOu have the length of the kayak. A bamboo pole is light, and making an antenna out of wire won't burden the pole. The real issue, I'd say, is figuring out something to put on the kayak to hold the pole. For emergencies, you can probably just have some fishing line tied to the top of the pole, and hold that as a "guy wire". If there was some way to hold the oar against the kayak, some clip on antenna that used the oar as a mast would be better than nothing, and of course doesn't require an extra pole. A bit of height probably does make an improvement, after that the "mast" has to get higher and higher to be useful. Bamboo poles are not all that light and they get water logged. Everything on a kayak gets wet. I was thinking of the bamboo stakes sold for tying plants to. Those are thin, but so long as the antenna is made of wire, and thus light, would work fine. I've used the stakes, because they were handy, to get a TV loop up a bit higher to scan the channels on the tv set. But I wasn't thinking of the water, and you're right, they wouldn't hold up after being kept wet a few times. How about fibreglass? Those flags seen on bicycles to give some height for oncoming vehicles, one of those might do. Or I have a vague memory of seeing such things sold for kayaks, to be seen a bit sooner than when a bigger boat stumbles on them. If they have them for kayaks, that's a good route to take, they would come with something to use to mount on the kayak. Michael |
#39
|
|||
|
|||
Antenna for Marine VHF
On 4/25/2017 1:46 PM, Michael Black wrote:
On Mon, 24 Apr 2017, rickman wrote: On 4/24/2017 3:44 PM, Michael Black wrote: On Sun, 23 Apr 2017, rickman wrote: On 4/23/2017 4:26 PM, Jeff Liebermann wrote: On Sun, 23 Apr 2017 15:16:40 -0400, rickman wrote: I said the particular case I was being asked about was not over salt water. I didn't say it was on a river. The particular case is for use on the Great Lakes. It's my understanding the propagation over the Great Lakes is similar to that over the ocean. However, I have no experience on the Great Lakes. I believe the issue of salt water came up because of a materials concern, aluminum vs. stainless steel. Your info is helpful. Thanks. Y're welcome. I mentioned the problem to a friend who was into kayaking when he was younger. He said that kayaks often carry push poles to get them off the rocks. These are often used as an improvised distress flag mast. I found this one: https://thesuperstick.com/product/push-pole/ which goes to 17ft extended. Hopefully, there are cheaper models. Not sure who told you about "push poles", but I've never run into kayaker with a push pole. If you get on rocks, you have a paddle. I don't even know where you would stow a push ploe. Much better to not get on the rocks. YOu have the length of the kayak. A bamboo pole is light, and making an antenna out of wire won't burden the pole. The real issue, I'd say, is figuring out something to put on the kayak to hold the pole. For emergencies, you can probably just have some fishing line tied to the top of the pole, and hold that as a "guy wire". If there was some way to hold the oar against the kayak, some clip on antenna that used the oar as a mast would be better than nothing, and of course doesn't require an extra pole. A bit of height probably does make an improvement, after that the "mast" has to get higher and higher to be useful. Bamboo poles are not all that light and they get water logged. Everything on a kayak gets wet. I was thinking of the bamboo stakes sold for tying plants to. Those are thin, but so long as the antenna is made of wire, and thus light, would work fine. I've used the stakes, because they were handy, to get a TV loop up a bit higher to scan the channels on the tv set. But I wasn't thinking of the water, and you're right, they wouldn't hold up after being kept wet a few times. How about fibreglass? Those flags seen on bicycles to give some height for oncoming vehicles, one of those might do. Or I have a vague memory of seeing such things sold for kayaks, to be seen a bit sooner than when a bigger boat stumbles on them. If they have them for kayaks, that's a good route to take, they would come with something to use to mount on the kayak. I think the best fiberglass for a marine VHF antenna would be the stuff you can get when you buy a marine VHF antenna. lol If you are talking about a simple wire the paddle would be ok. They are typically around 7 foot long. Clip the wire on the end of the paddle and Bob's your uncle. It's not like you will be transmitting for hours, so you can just hold the paddle up. Yesterday I couldn't think of the term for the antenna style they use in the commercial marine VHF antennas, but I believe it is called "co-linear" or something like that. It is a bunch of coax sections connected inner to outer at specific lengths. I have never seen a Ham recommend using that type. But I guess Hams go more for permanent installations with ground planes of some type. The co-linear needs no ground plane I believe. -- Rick C |
#40
|
|||
|
|||
Antenna for Marine VHF
On 4/25/2017 12:07 PM, Fred McKenzie wrote:
In article , rickman wrote: On 4/24/2017 3:39 PM, Michael Black wrote: On Sun, 23 Apr 2017, highlandham wrote: On 23/04/17 04:03, Jeff Liebermann wrote: quote ===== When you're on the water line, antenna height does make a big difference. Prepare a roll of coax cable setup as an RF extension cable. Attach connectors and adapters so that they fit the radio and the antenna. If in trouble at sea, lash the antenna to the top of a pole or oar to gain altitude. A separate antenna, such as a common ground plane or coax sleeve antenna at the end of the coax cable would make a better antenna than a rubber ducky. unquote ===== A simple alternative to the J-Pole antenna would be a ground plane antenna made of welding rod material on an SO-239 socket with a 4 hole square flange with a vertical quarter wave radiator and 4 hinged radial elements,the latter under 45 degrees when in use . The SO-239 socket would be connected to a PL-259 connector and a suitable length of coax. But on a kayak? It won't do much good lying on the kayak, and unless you get it high enough (which has problems in itself), you'll poke your eye out. Why not go for something that doesn't need horizontal radials. Actually I gave this antenna some thought. If the radials were attached by some sort of hinge for example a heavy braid, they could fold up while still being electrically attached. The antenna could slide into a tube when not in use. It might be a bit complex to rig up, but this is the sort of thing I can give some thought to and maybe come up with something workable. Back to the J-Pole! You can make a light, flexible J-Pole out of 300 Ohm twinlead. Feed it with RG-174 cable. Use some kind of oar or pole to raise it when needed. I wouldn't know where to begin in sizing the components. -- Rick C |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Marine antenna ?? | Antenna | |||
Marine 2m Antenna wanted | Antenna | |||
help with a marine antenna | Antenna | |||
FA: CB ANTENNA M'CYLE-MARINE-BOAT>ANTENNA SPECIALIST MR306 | CB | |||
Is it a CB or VHF marine antenna? | Antenna |