Home |
Search |
Today's Posts |
|
#1
![]() |
|||
|
|||
![]()
On 4/23/2017 2:31 PM, Jeff Liebermann wrote:
On Sun, 23 Apr 2017 12:00:09 -0400, rickman wrote: Will 5 watts be heard that far away? Let's see what the Fiis equation says, assuming line of sight, perfect conditions, and no obstructions: http://www.proxim.com/products/knowledge-center/calculations/calculations-system-operating-margin-som Distance = 20 statute miles Operating frequency is about 156MHz Rubber ducky antenna gain is about -3dB Coax cable loss is zero. 5 watts tx power is +37dBm 25 watts tx power is +44dBm Rx sensitivity is 0.18uV = -122dBm/12dB SINAD Plugging into the above calculator, I get for 5 watts: 106.5 dB path loss -75.5 dbm rx signal strength 46.5 dB fade margin In other words, with this arrangement, your receive signal is 46.5dB stronger than the minimum level (12dB SINAD) necessary to hear a fairly weak and noisy signal. You should theoretically have no problems being heard at 20 miles. However, that's theory, not practice. At 156 MHz, the Fresnel zone is rather large. Quite a bit of signal is lost bouncing off the water surface, or being absorbed. There are waves that get in the way. The curvature of the earth raises the wave height at mid span, resulting in more blockage. My experience is about 5 miles maximum for reliable communications between two handhelds over water. Icom sorta suggests 3 to 8 miles: https://www.westmarine.com/WestAdvisor/Selecting-a-VHF-Handheld-Radio Please read the "What are the limits of range and power?" near the bottom of the page. Propagation over water is also full of oddities and anomalies: "The propagation of VHF and UHF radio waves over sea paths " https://pdfs.semanticscholar.org/a6ca/1fe1ca92e96a7e7150217b265816891b102e.pdf I've been in situations where I can see the person or station that I'm trying to communicate but because of inversion layers and surface reflections, the signal was weak, variable, or gone. You mentioned that it's not over salt water. In that case, land topography has a huge effect on propagation. If your friend is in a river canyon, raising the antenna a few feet isn't going to do anything useful. For such situations, land the kayak, climb the walls of the canyon, and try the radio where there's fewer obstacles. 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. Other uses I might have at other times would likely be on salt water such as the Chesapeake Bay and tributaries or the Atlantic ocean. Your info is helpful. Thanks. -- Rick C |
#2
![]() |
|||
|
|||
![]()
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. 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. To attach an antenna, there's the usual roll of coax cable and some kind of temporary mounting clip. Perhaps something like this, but with lower loss coax cable: http://www.dhgate.com/product/nagoya-rb-clp-window-clip-mount-rg-174-u/176624090.html https://www.aliexpress.com/store/product/NAGOYA-RB-CLP-Window-Clip-Mount-RG-174-U-3m-Cable-BNC-for-walkie-talkie-Radio/1295452_32312249435.html Or, just an L-bracket with a connector attached. Or, a big rubber band. Whatever gets the antenna higher. You're on your own on how to keep the push pole mast upright. Vessels sometimes carry "emergency" antennas. The idea is that if the main antenna is in some way lost, the emergency antenna would be substituted. Examples: https://www.westmarine.com/buy/shakespeare--stowaway-emergency-vhf-antenna--519058 http://shakespeare-ce.com/marine/product/sl-156-emergency-vhf-antenna/ They're usually small and have little gain, but might offer some useful ideas. Lunch beckons... -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#3
![]() |
|||
|
|||
![]()
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. To attach an antenna, there's the usual roll of coax cable and some kind of temporary mounting clip. Perhaps something like this, but with lower loss coax cable: http://www.dhgate.com/product/nagoya-rb-clp-window-clip-mount-rg-174-u/176624090.html https://www.aliexpress.com/store/product/NAGOYA-RB-CLP-Window-Clip-Mount-RG-174-U-3m-Cable-BNC-for-walkie-talkie-Radio/1295452_32312249435.html Or, just an L-bracket with a connector attached. Or, a big rubber band. Whatever gets the antenna higher. You're on your own on how to keep the push pole mast upright. Vessels sometimes carry "emergency" antennas. The idea is that if the main antenna is in some way lost, the emergency antenna would be substituted. Examples: https://www.westmarine.com/buy/shakespeare--stowaway-emergency-vhf-antenna--519058 http://shakespeare-ce.com/marine/product/sl-156-emergency-vhf-antenna/ They're usually small and have little gain, but might offer some useful ideas. If I find a kayak with a roll down window I'll get one of these and try it. A kayak is not a large fishing vessel. It is a small, narrow boat with little deck space. I had a deck mounted light on a two foot pole and it was always a problem by being in the way, especially when getting in and out of the boat. You wouldn't believe how stupid and crappy many kayaking products are. I seriously doubt any sort of deck mounted antenna will be acceptable to a serious kayaker, but if it is unobtrusive and light enough it might work. There are a number of commercial marine VHF antennas that should do the job. The trick will be finding one that works as well on a kayak deck as a power boat. That's the main reason why kayakers use hand held radios. -- Rick C |
#4
![]() |
|||
|
|||
![]()
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 |
#5
![]() |
|||
|
|||
![]()
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 |
#6
![]() |
|||
|
|||
![]()
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 |
#7
![]() |
|||
|
|||
![]()
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 |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
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 |