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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 |
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