|
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! |
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. |
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 |
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! |
Directional antenna in the 215 to 218 MHz band
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. You might do a bit of research on the equipment that various animal tracking organizations use. They tend to use the 215 - 218 MHz band for tracking various animal species, and the equipment should suit your needs also. Ed K7AAT |
Directional antenna in the 215 to 218 MHz band
|
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. |
Directional antenna in the 215 to 218 MHz band
wrote in message
... 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 Thanks Kingfish. That's pretty cool! It's actually much like what we're using now... A 4 element Yagi, though ours don't have the flexible elements like one made of tape measure. |
Directional antenna in the 215 to 218 MHz band
"Ed_G" wrote in message You might do a bit of research on the equipment that various animal tracking organizations use. They tend to use the 215 - 218 MHz band for tracking various animal species, and the equipment should suit your needs also. Thanks Ed. That's a good idea, and you're exactly right... what we're doing looks just like what you'd see on a television nature show where someone had a radio collar on a lion or something like that. We're applying the same technology to Alzheimer's patients who are at risk of wandering. |
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 |
Directional antenna in the 215 to 218 MHz band
Thanks Ed. That's a good idea, and you're exactly right... what we're doing looks just like what you'd see on a television nature show where someone had a radio collar on a lion or something like that. We're applying the same technology to Alzheimer's patients who are at risk of wandering. You're welcome. You might also consider some of the new GPS products.... often made for tracking cars... but some small enough to place on a person. You could sit at the comfort of a computer and track them! Ed :^) |
Directional antenna in the 215 to 218 MHz band
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! I just did a quick simulation on EZNEC of your proposed Quad. At 215 mhz the element spacing on the boom is about 1 foot. That means a 4 element yagi or quad should come out to 3 feet long. Similarly, the element loops will be about 1 foot square. With no matching attempted 2:1 Swr is easily achieved. If you are so inclined you could model this antenna with the Demo version of EZNEC. You could also prototype one or more on the kitchen table with masking tape and sticks! I would think the additional gain of the Quad would make it desirable to drop back to three elements to reduce the size. John Ferrell W8CCW Beware of the dopeler effect (pronounced dope-ler). That's where bad ideas seem good if they come at you fast enough. |
Directional antenna in the 215 to 218 MHz band
"Ed_G" wrote in message You're welcome. You might also consider some of the new GPS products.... often made for tracking cars... but some small enough to place on a person. You could sit at the comfort of a computer and track them! GPS was discussed in our training, with the main drawback being that if the patient was in a building or under a canopy of trees, etc, there would be no signal. |
Directional antenna in the 215 to 218 MHz band
"John Ferrell" wrote in message I just did a quick simulation on EZNEC of your proposed Quad. At 215 mhz the element spacing on the boom is about 1 foot. That means a 4 element yagi or quad should come out to 3 feet long. Similarly, the element loops will be about 1 foot square. That sounds *exactly* like the one that we used in our training. The guy who made it said that he used an antenna design calculator on the internet to come up with the layout. I'm still awaiting plans from him, and in the meantime I'm interested in seeing if I can do it myself for the technical exercise. If you are so inclined you could model this antenna with the Demo version of EZNEC. You could also prototype one or more on the kitchen table with masking tape and sticks! I'm going to take a look at EZNEC and also google around for "Cubical Quad" as suggested upthread by John KD5YI. So far this looks like exactly what I'm looking for. Thanks! |
Directional antenna in the 215 to 218 MHz band
On Mon, 24 Mar 2008 03:28:19 GMT, "usmcbrat"
wrote: "John Ferrell" wrote in message I just did a quick simulation on EZNEC of your proposed Quad. At 215 mhz the element spacing on the boom is about 1 foot. That means a 4 element yagi or quad should come out to 3 feet long. Similarly, the element loops will be about 1 foot square. That sounds *exactly* like the one that we used in our training. The guy who made it said that he used an antenna design calculator on the internet to come up with the layout. I'm still awaiting plans from him, and in the meantime I'm interested in seeing if I can do it myself for the technical exercise. Again, I would suggest a search of the Google archives in research of the term "Foxhunting." Antennas with such gain may appear the obvious choice by graphics of their radiation characteristics, but there are more matters to location than putting a signal in the peak of a lobe. I have a friend who has lead many Search and Rescue operation in the city looking for patients who have "wandered away." Quite frequently they passed by their quarry (quite closely) simply because of the urban clutter that presents antennas with these characteristics very confusing results. On the other hand, and as many sailors may attest, sharp nulls are often more compelling location indicators. Such an antenna as the W8JK with variable phasing can give you both sharp nulls and general gain (through careful selection of the drive point) on a shorter boom (and could be designed in the way of a quad). 73's Richard Clark, KB7QHC |
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 |
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 |
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 |
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 |
Directional antenna in the 215 to 218 MHz band
"Mark" wrote in message ... How about a small Yagi made with "rubber duckies"? I admit it, I don't know what you mean. :) |
Directional antenna in the 215 to 218 MHz band
In article U7YGj.9289$Oj5.166@trnddc06,
"usmcbrat" wrote: "Mark" wrote in message ... How about a small Yagi made with "rubber duckies"? I admit it, I don't know what you mean. :) USMCBrat- I think the cubical quad may be the best antenna for your situation, but there are other options. "Rubber duckie" refers to the shortened rubber-coated antenna on a walkie talkie. If several of these were arranged as a yagi, they would not have the sharp points your full size yagi has. Another is called a "Doppler Direction Finder", and requires an electronics package. It has 4 vertical antennas arranged in a square on a metal plate. Take a look at http://www.ramseyelectronics.com/cgi...dd=action&key= DDF1 for an example of this kind of system. The vertical antennas might be "rubber duckies" as well. Fred K4DII |
Directional antenna in the 215 to 218 MHz band
Another is called a "Doppler Direction Finder", and requires an
electronics package. It has 4 vertical antennas arranged in a square on a metal plate. Take a look at http://www.ramseyelectronics.com/cgi...dd=action&key= DDF1 for an example of this kind of system. The vertical antennas might be "rubber duckies" as well. Fred K4DII I would also have a search for 'Handifinder', it is a simplified version of the above that uses 2 small loop antennas and is easily hand portable. It is cheap and easy to build and I think kits are available. It does have a 180 degree ambiguity but in real use that is not a great problem. 73 Jeff |
| All times are GMT +1. The time now is 09:37 AM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com