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Directional antenna in the 215 to 218 MHz band
Hi Folks:
I'm looking to make a directional antenna in the 215 to 218 MHz band (215 if that's too broad), used for location of dementia patients who have wandered away from their caregivers. I'm a volunteer with an organization that locates these people. They wear a tiny transmitter which emits a chirp that can be heard from 1-2 miles on the ground and 8-10 miles via helicopter. I'm somewhat new to the program, and I'd like to do some investigation on my own regarding antenna types that would be useful, and I hope you'll all grant me a few questions. My needs are this.... the antenna must be as directional as possible. It must be most efficient in the 215 to 218 MHz band 215 is what our patients are on right now, though after we fill up that range we have licensed through 218 MHz. It must be easy for an individual to carry, and portable enough to carry through any type of terrain. It must be shaped in such a way that it's relatively safe and easy to use in an enclosed area, either in a helicopter or a car. Currently the agency is using a 4 element Yagi, which works well, but has the drawback of being a real eye-poker when used in close quarters, and in fact the California Highway Patrol will not allow them to be used in their helicopters because of that reason. One of our Search & Rescue guys built his own 4 element Quad Yagi out of some 1/2" PVC pipe and other parts that are readily available at any Home Depot. It has greater sensitivity than our stock antenna, and the CHP has said that it's OK to use in their helicopters. Rather than 4 horizontal straight beams it has 4 squarish beams, with no points to poke people's eyes out. I'm still waiting to get the plans from him for that antenna, and I though that in the meantime I'd ask in here if any of you had some interesting leads for me to follow. Many thanks! |
#2
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Directional antenna in the 215 to 218 MHz band
Clarification:
216 MHz is what we're using now. We're getting away from 215 because of interference with digital TV. |
#3
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Directional antenna in the 215 to 218 MHz band
On Thu, 20 Mar 2008 05:44:50 GMT, "usmcbrat"
wrote: My needs are this.... the antenna must be as directional as possible. It must be most efficient in the 215 to 218 MHz band 215 is what our patients are on right now, though after we fill up that range we have licensed through 218 MHz. It must be easy for an individual to carry, and portable enough to carry through any type of terrain. It must be shaped in such a way that it's relatively safe and easy to use in an enclosed area, either in a helicopter or a car. Currently the agency is using a 4 element Yagi, which works well, but has the drawback of being a real eye-poker when used in close quarters, and in fact the California Highway Patrol will not allow them to be used in their helicopters because of that reason. Hi USMCbrat, Research the Google newsgroups (for this newsgroup specifically) archive with the keyword "foxhunt." There are more issues than just directionality to be considered. ARMYbrat Richard Clark, KB7QHC |
#4
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Directional antenna in the 215 to 218 MHz band
"Richard Clark" wrote in message Research the Google newsgroups (for this newsgroup specifically) archive with the keyword "foxhunt." There are more issues than just directionality to be considered. ARMYbrat Richard Clark, KB7QHC Thanks ARMYbrat. This USMCbrat appreciates it, and everything else! Most of what I've found thus far is about the same as what we're currently using, which is a flat 4 element Yagi. I may not be versed enough to describe the plans I'm looking for, but when I find them I'll post here. The antenna I'm looking for is perhaps better described as a 4 element Box or Cube Yagi where the frame is built of 1/2 inch PCV and the elements are fairly heavy guage wire. There's no sharp points to hurt someone's eye, which is frowned upon by the California Highway Patrol for use in their helicopters. There's a guy that I trained with who has the plans and hasn't yet gotten back to me with them, but I'll be persistent and let people here know when I get the plans. |
#5
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Directional antenna in the 215 to 218 MHz band
"usmcbrat" wrote in message news:5_cFj.257$rb6.143@trnddc01... "Richard Clark" wrote in message Research the Google newsgroups (for this newsgroup specifically) archive with the keyword "foxhunt." There are more issues than just directionality to be considered. ARMYbrat Richard Clark, KB7QHC Thanks ARMYbrat. This USMCbrat appreciates it, and everything else! Most of what I've found thus far is about the same as what we're currently using, which is a flat 4 element Yagi. I may not be versed enough to describe the plans I'm looking for, but when I find them I'll post here. The antenna I'm looking for is perhaps better described as a 4 element Box or Cube Yagi where the frame is built of 1/2 inch PCV and the elements are fairly heavy guage wire. There's no sharp points to hurt someone's eye, which is frowned upon by the California Highway Patrol for use in their helicopters. There's a guy that I trained with who has the plans and hasn't yet gotten back to me with them, but I'll be persistent and let people here know when I get the plans. Search Google with "cubical quad" and you'll find what you want, I think. There are even some calculators for this type antenna listed. http://en.wikipedia.org/wiki/Quad_antenna 73, John |
#6
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Directional antenna in the 215 to 218 MHz band
"usmcbrat" wrote in message news:5_cFj.257$rb6.143@trnddc01... ..I'll be persistent and let people here know when I get the plans. I still don't have "plans", but here's a picture. Turns out it was a 3 element. My apologies for such an inaccurate memory. http://img168.imageshack.us/img168/5...ining1shk5.jpg |
#7
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Directional antenna in the 215 to 218 MHz band
"usmcbrat" wrote in message news:01HGj.3370$rb6.1690@trnddc01... "usmcbrat" wrote in message news:5_cFj.257$rb6.143@trnddc01... ..I'll be persistent and let people here know when I get the plans. I still don't have "plans", but here's a picture. Turns out it was a 3 element. My apologies for such an inaccurate memory. http://img168.imageshack.us/img168/5...ining1shk5.jpg Hi "UMC" Is it practical to mount the antenna outside toe helicopter? I once designed an antenna system for military helicopter VHF homing. I used two dipoles made of foil taped to the plastic windshield. It worked. The idea was/is simple, but you'd need to build a seperate electronic device to go between the antenna and the receiver. And, you'd (of course) need to manuver the helicopter rather than twist/turn the antenna, because, the helicopter would be the antenna. Jerry KD6JDJ |
#8
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Directional antenna in the 215 to 218 MHz band
I still don't have "plans", but here's a picture. *Turns out it was a 3 element. *My apologies for such an inaccurate memory. How about a small Yagi made with "rubber duckies"? Mark |
#9
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Directional antenna in the 215 to 218 MHz band
"Jerry" wrote in message news:SeOGj.4383$Dv5.2658@trnddc02... Is it practical to mount the antenna outside toe helicopter? I once designed an antenna system for military helicopter VHF homing. I used two dipoles made of foil taped to the plastic windshield. It worked. The idea was/is simple, but you'd need to build a seperate electronic device to go between the antenna and the receiver. And, you'd (of course) need to manuver the helicopter rather than twist/turn the antenna, because, the helicopter would be the antenna. Hi Jerry: I guess if the helicopter was specifically part of the searching agency then you could do something like that. I'm not sure if they'd ever do that. The choppers and pilots are usually "on loan" from whatever agency is available to help when someone's lost. The CHP has some, most Sheriff's departments, Feds, Military, State Police, etc. When a person is lost, people seem to come out of the woodwork with the desire to help. That often includes agencies that own helicopters. While I'm now a certified trainer because of my classroom time, I'm still a brand-newbie to search and rescue, and have never been on a "real" search for a missing person. I've located hidden transmitters on dozens of occasions, either hidden on a person who was part of the training, or just plain hidden. If I can get within a couple of miles of one of the transmitters I can normally go straight to it, even if it's down a drainpipe, under a bridge, or behind the coffee maker in a restaurant... it doesn't really matter much where it is located. More of our training is related to understanding people with Alzheimer's and other forms of dementia than is related to actual radio work, and rightfully so. There's much to study on the human side of it. One of my greatest fears now is that I'll search for a person who is at a significant danger of being injured and is lost in a giant crowd of people, and they don't want to be found. I feel uncomfortable "pointing" the antenna around crowds of people for obvious social and psychological reasons. An example might be someone "lost" in Time's Square on New Years Eve.... the very thought shivers me timbers! Luckily, being from Central California, I'll be much more likely to be searching orange groves than giant crowds. Interestingly, orange groves absorb a signal much more than I had thought they would, and, the signal propagates much better down the rows than across the rows. The trees were laden with oranges and I could barely hear a signal from one of our guys who was purposely trying to avoid us. He was literally 5 or 6 rows in (across) and I could hardly hear the signal. Once we got to the end of the grove and got to look down the rows, the signal jumped. Thanks again for all of your help! MB |
#10
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Directional antenna in the 215 to 218 MHz band
Do a search for "tape measure antenna". It is a simple to build yagi
antenna made of pvc pipe with elements made from a metal measuring tape. You can rescale it to your frequency. Kingfish On Thu, 20 Mar 2008 05:44:50 GMT, "usmcbrat" wrote: Hi Folks: I'm looking to make a directional antenna in the 215 to 218 MHz band (215 if that's too broad), used for location of dementia patients who have wandered away from their caregivers. I'm a volunteer with an organization that locates these people. They wear a tiny transmitter which emits a chirp that can be heard from 1-2 miles on the ground and 8-10 miles via helicopter. I'm somewhat new to the program, and I'd like to do some investigation on my own regarding antenna types that would be useful, and I hope you'll all grant me a few questions. My needs are this.... the antenna must be as directional as possible. It must be most efficient in the 215 to 218 MHz band 215 is what our patients are on right now, though after we fill up that range we have licensed through 218 MHz. It must be easy for an individual to carry, and portable enough to carry through any type of terrain. It must be shaped in such a way that it's relatively safe and easy to use in an enclosed area, either in a helicopter or a car. Currently the agency is using a 4 element Yagi, which works well, but has the drawback of being a real eye-poker when used in close quarters, and in fact the California Highway Patrol will not allow them to be used in their helicopters because of that reason. One of our Search & Rescue guys built his own 4 element Quad Yagi out of some 1/2" PVC pipe and other parts that are readily available at any Home Depot. It has greater sensitivity than our stock antenna, and the CHP has said that it's OK to use in their helicopters. Rather than 4 horizontal straight beams it has 4 squarish beams, with no points to poke people's eyes out. I'm still waiting to get the plans from him for that antenna, and I though that in the meantime I'd ask in here if any of you had some interesting leads for me to follow. Many thanks! |
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