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#11
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Antenna for Marine VHF
In article , rickman
wrote: Can you explain what would be preferable about the J-pole antenna? One big disadvantage is that it appears to be more like 6 foot long for 2 meter use. That could be rather heavy and clumsy on a kayak. Rick- You are correct about the size. On the other hand, any separate antenna for the VHF Marine band will be a bit clumsy on a kayak. The "J" end of a J-pole is used to match a cable to the high impedance of the end of a half wave element. One advantage of a vertical half wave entenna is that it directs more energy towards the horizon, compared to a quarter wave ground plane antenna. Jeff Liebermann's analysis sounds like the best approach to VHF on a kayak. But no matter which way you go, you are transmitting from a point close to the water. You are limited to line-of-sight to another kayak. Range to a base station will be mostly determined by the height of the base station antenna. Fred |
#12
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Antenna for Marine VHF
On 4/22/2017 12:25 PM, Fred McKenzie wrote:
In article , rickman wrote: Can you explain what would be preferable about the J-pole antenna? One big disadvantage is that it appears to be more like 6 foot long for 2 meter use. That could be rather heavy and clumsy on a kayak. Rick- You are correct about the size. On the other hand, any separate antenna for the VHF Marine band will be a bit clumsy on a kayak. The "J" end of a J-pole is used to match a cable to the high impedance of the end of a half wave element. One advantage of a vertical half wave entenna is that it directs more energy towards the horizon, compared to a quarter wave ground plane antenna. Jeff Liebermann's analysis sounds like the best approach to VHF on a kayak. But no matter which way you go, you are transmitting from a point close to the water. You are limited to line-of-sight to another kayak. Range to a base station will be mostly determined by the height of the base station antenna. That is an issue I have already explored. There is not much hard information available, but it would appear that the rubber ducky antenna is adequate for use from one kayak to another for the most part. BTW, that range is twice the distance to the horizon which is about two nautical miles. Communications to a land station such as the Coast Guard would be much longer given the height of their antennas, unless your transmitted power level is too low to reach them. You might be able to receive their transmissions which are at a higher power, but they might not be able to hear your transmissions. In that case a better antenna might make the difference between rescue and not. I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A cordless remote would be the best option I believe and I expect they are available. A power boost from 5W to 25W would easily beat the performance of a larger antenna. Not sure how much this would weigh with a battery, but I don't think the battery would need to be so large. It's not like 25W has to be used for every transmission. -- Rick C |
#13
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Antenna for Marine VHF
On Sat, 22 Apr 2017, Fred McKenzie wrote:
In article , rickman wrote: Can you explain what would be preferable about the J-pole antenna? One big disadvantage is that it appears to be more like 6 foot long for 2 meter use. That could be rather heavy and clumsy on a kayak. Rick- You are correct about the size. On the other hand, any separate antenna for the VHF Marine band will be a bit clumsy on a kayak. The "J" end of a J-pole is used to match a cable to the high impedance of the end of a half wave element. One advantage of a vertical half wave entenna is that it directs more energy towards the horizon, compared to a quarter wave ground plane antenna. Jeff Liebermann's analysis sounds like the best approach to VHF on a kayak. But no matter which way you go, you are transmitting from a point close to the water. You are limited to line-of-sight to another kayak. Range to a base station will be mostly determined by the height of the base station antenna. And with a kayak, the issue is less about "antenna gain" than that there's nothing with height on a kayak, and it's very low in the water. Figure out some sort of "mast" and the problem is close to solved. Once you have height, the actual antenna type matters less. I seem to recall George Dyson put sails on some of his really big kayaks, so that's an option, and the mast would provide some height for the antenna. Michael |
#14
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Antenna for Marine VHF
On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote:
... it would appear that the rubber ducky antenna is adequate for use from one kayak to another for the most part. BTW, that range is twice the distance to the horizon which is about two nautical miles. Conservative radio range on VHF is: Nautical_Miles = 1.225 * sqrt(antenna_ht_feet) Statute_Miles = 1.415 * sqrt(antenna_ht_feet) km = 4.124 * sqrt(antenna_ht_feet) Mo http://www.qsl.net/kd4sai/distance.html Communications to a land station such as the Coast Guard would be much longer given the height of their antennas, unless your transmitted power level is too low to reach them. You might be able to receive their transmissions which are at a higher power, but they might not be able to hear your transmissions. In that case a better antenna might make the difference between rescue and not. 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. I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A higher power transmitter will help the Coast Guard hear you but will do nothing for you hearing the Coast Guard. More antenna gain, and a higher antenna are better solutions. A cordless remote would be the best option I believe and I expect they are available. A power boost from 5W to 25W would easily beat the performance of a larger antenna. Not sure how much this would weigh with a battery, but I don't think the battery would need to be so large. It's not like 25W has to be used for every transmission. The biggest headache with using a 25 watt radio on battery power is that the receive current drain is rather high thanks to the display backlighting. For example: http://www.standardhorizon.com/indexVS.cfm?cmd=DisplayProducts&ProdCatID=83&encPr odID=1BFCB309CEE0FEE9385740D0F23313FA&DivisionID=3 &isArchived=0 0.45A very low audio 0.8A full audio 5.0A 25 w transmit 1.0A 1 w transmit So, let's say you start off with a 12V 7A-hr SLA battery commonly found in a UPS. You don't want to kill the battery so let's only drain it down to 40% capacity. That would give you: 12V * 7A-hr * 0.6 = 50.4 watt-hrs In 25 watt transmit, that give you: 50.4 watt-hrs / (12v * 5A) = 0.84 hrs * 60 min/hr = 50.4 minutes talk time That's actually quite a long time for a fairly small battery. However, if you leave it running in receive, you get: 50.4 watt-hrs / (12v * 0.45A) = 6.22 hrs listen time That's at low audio. If you wanted to hear something or transmit, it would be much lower. You could do better with a LiIon battery pack. The problem is that most such packs either 3 cells, which yields about 10.8V which is insufficient, or 4 cells, which could be as high as: 4.1v * 4 = 16.4v which might be over the maximum voltage rating for the radio. The Standard GX1600 is rated for 11 to 16.5V operating voltage, so you should be ok with 4 cells. Yep, a 25 watt radio might work. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#15
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Antenna for Marine VHF
On Sat, 22 Apr 2017 20:03:49 -0700, Jeff Liebermann
wrote: Conservative radio range on VHF is: Nautical_Miles = 1.225 * sqrt(antenna_ht_feet) Statute_Miles = 1.415 * sqrt(antenna_ht_feet) km = 4.124 * sqrt(antenna_ht_feet) Something is wrong with the km line above. Perhaps the antenna height should be in meters? Or, the constant should be 2.278. |
#16
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Antenna for Marine VHF
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#17
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Antenna for Marine VHF
On 4/23/2017 10:17 AM, Ralph Mowery wrote:
In article , says... On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote: I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A higher power transmitter will help the Coast Guard hear you but will do nothing for you hearing the Coast Guard. More antenna gain, and a higher antenna are better solutions. Going from 5 to 25 watts of FM will gain almost nothing. Raising the antenna several feet from the sitting down position will gain a lot. Are you saying that a hand held 5 watt transceiver with a rubber ducky antenna will reach all receivers because of the line of sight limitation? Is that true even for contacting a land station with a 200 foot high antenna? A 3 foot high antenna and a 200 foot high antenna give nearly 20 statute miles of range. Will 5 watts be heard that far away? -- Rick C |
#18
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Antenna for Marine VHF
On 4/23/2017 12:00 PM, rickman wrote:
On 4/23/2017 10:17 AM, Ralph Mowery wrote: In article , says... On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote: I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A higher power transmitter will help the Coast Guard hear you but will do nothing for you hearing the Coast Guard. More antenna gain, and a higher antenna are better solutions. Going from 5 to 25 watts of FM will gain almost nothing. Raising the antenna several feet from the sitting down position will gain a lot. Are you saying that a hand held 5 watt transceiver with a rubber ducky antenna will reach all receivers because of the line of sight limitation? Is that true even for contacting a land station with a 200 foot high antenna? A 3 foot high antenna and a 200 foot high antenna give nearly 20 statute miles of range. Will 5 watts be heard that far away? Opps, make that nearly 20 nautical miles. It's over 22 statute miles. -- Rick C |
#19
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Antenna for Marine VHF
rickman wrote:
On 4/23/2017 10:17 AM, Ralph Mowery wrote: In article , says... On Sat, 22 Apr 2017 12:43:39 -0400, rickman wrote: I've also considered the possibility of a higher powered unit built into the boat with a small remote control. A higher power transmitter will help the Coast Guard hear you but will do nothing for you hearing the Coast Guard. More antenna gain, and a higher antenna are better solutions. Going from 5 to 25 watts of FM will gain almost nothing. Raising the antenna several feet from the sitting down position will gain a lot. Are you saying that a hand held 5 watt transceiver with a rubber ducky antenna will reach all receivers because of the line of sight limitation? Is that true even for contacting a land station with a 200 foot high antenna? A 3 foot high antenna and a 200 foot high antenna give nearly 20 statute miles of range. Will 5 watts be heard that far away? Radio amateurs have launched satellites which usually have about 1 to 5 W of power on VHF and UHF. Those can be clearly heard on a portable with a very small antenna even when 2000-3000km away. The loss of signal on line of sight is easy to overcome with narrow band modulation and this kind of power. It is the "beyond line of sight" attennuation that is the problem. Everything you can do to remove that will help a lot more than power. Today I was working at the repeater in our local radio/tv tower. We were at 220m above ground level and it was easy to work over a repeater about 80km away from us using only a handy with 1W of output. Only because at that height this is (almost) line of sight. |
#20
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Antenna for Marine VHF
In article , rickman
wrote: A 3 foot high antenna and a 200 foot high antenna give nearly 20 statute miles of range. Will 5 watts be heard that far away? Rick- I have not done the calculations, but think your limit is line-of-sight rather than power. I once talked 50 miles to an aircraft on Two Meters, using a 1 watt handheld with rubber ducky antenna. This assumes the Coast Guard does not have their squelch set too tight. Fred |
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