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#1
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Potted 900MHz PCB antenna
Hi,
I have an interesting project! I am using a RF receiver device which has a 50 Ohm RF input. I want to use a PCB printed antenna on FR4 board, not unusual you say. but I need to pot the whole PCB in resin to make it waterproof. The receiver only needs to work when floating on water! Has anyone any experience in PCB antenna who would be so kind to comment on the effects, and possible actions to counter any effects, of the potting. The resin is much like araldite. Any thoughts much appreciated. Will |
#2
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On Tue, 14 Oct 2003 18:27:50 +0000 (UTC), "Will Reeve"
wrote: Hi, I have an interesting project! I am using a RF receiver device which has a 50 Ohm RF input. I want to use a PCB printed antenna on FR4 board, not unusual you say. but I need to pot the whole PCB in resin to make it waterproof. The receiver only needs to work when floating on water! Has anyone any experience in PCB antenna who would be so kind to comment on the effects, and possible actions to counter any effects, of the potting. The resin is much like araldite. Any thoughts much appreciated. Will Hi Will, Look into conformal coating as an alternative. Or simply mix acetone and RTV to create one and paint it on. To cut down on water losses, it would do well to provide an air jacket around the antenna elements that is roughly a tenth wavelength in diameter (and from the tips). 73's Richard Clark, KB7QHC |
#3
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Will Reeve wrote:
Hi, I have an interesting project! I am using a RF receiver device which has a 50 Ohm RF input. I want to use a PCB printed antenna on FR4 board, not unusual you say. but I need to pot the whole PCB in resin to make it waterproof. The receiver only needs to work when floating on water! Has anyone any experience in PCB antenna who would be so kind to comment on the effects, and possible actions to counter any effects, of the potting. The resin is much like araldite. Any thoughts much appreciated. Will The potting compound will act as a dielectric load. My bet is that the dielectric constant will be about 3. Your antenna will have to shrink. If you know the dielectric properties of the potting compound, and your antenna is simple, then I might be able to run a simulation (and optimization) for you with IE3D.... I work with 900 MHz antennas on FR4 every day Wayne Shanks Senior RF and Antenna Engineer, Matrics Inc. |
#4
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If the antenna is in close proximity to water, the water's dielectric
constant of about 80 will have a profound effect, as will its very high loss. Roy Lewallen, W7EL Wayne Shanks wrote: Will Reeve wrote: Hi, I have an interesting project! I am using a RF receiver device which has a 50 Ohm RF input. I want to use a PCB printed antenna on FR4 board, not unusual you say. but I need to pot the whole PCB in resin to make it waterproof. The receiver only needs to work when floating on water! Has anyone any experience in PCB antenna who would be so kind to comment on the effects, and possible actions to counter any effects, of the potting. The resin is much like araldite. Any thoughts much appreciated. Will The potting compound will act as a dielectric load. My bet is that the dielectric constant will be about 3. Your antenna will have to shrink. If you know the dielectric properties of the potting compound, and your antenna is simple, then I might be able to run a simulation (and optimization) for you with IE3D.... I work with 900 MHz antennas on FR4 every day Wayne Shanks Senior RF and Antenna Engineer, Matrics Inc. |
#5
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www.fwt.niat.net
This dielectric embedded antennas are smaller than naturally occurs and yet have a net gain "Roy Lewallen" wrote in message ... If the antenna is in close proximity to water, the water's dielectric constant of about 80 will have a profound effect, as will its very high loss. Roy Lewallen, W7EL Wayne Shanks wrote: Will Reeve wrote: Hi, I have an interesting project! I am using a RF receiver device which has a 50 Ohm RF input. I want to use a PCB printed antenna on FR4 board, not unusual you say. but I need to pot the whole PCB in resin to make it waterproof. The receiver only needs to work when floating on water! Has anyone any experience in PCB antenna who would be so kind to comment on the effects, and possible actions to counter any effects, of the potting. The resin is much like araldite. Any thoughts much appreciated. Will The potting compound will act as a dielectric load. My bet is that the dielectric constant will be about 3. Your antenna will have to shrink. If you know the dielectric properties of the potting compound, and your antenna is simple, then I might be able to run a simulation (and optimization) for you with IE3D.... I work with 900 MHz antennas on FR4 every day Wayne Shanks Senior RF and Antenna Engineer, Matrics Inc. |
#6
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On Mon, 03 Nov 2003 17:00:58 GMT, "Marc H.Popek"
wrote: www.fwt.niat.net This dielectric embedded antennas are smaller than naturally occurs and yet have a net gain Hi Marc, Interesting sentence construction. A cogent question would reveal some perspective: How much would your 13dBi dielectric embedded antennas for TV Channel 2 weigh? 73's Richard Clark, KB7QHC |
#7
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"Marc H.Popek" wrote in message ... www.fwt.niat.net This dielectric embedded antennas are smaller than naturally occurs and yet have a net gain More correctly, they CLAIM a gain, relative to isotropic. If the antenna is smaller than a free space antenna, then it looses capture area. I would be very interested to know how they recoup that. I suspect these antennas might need some power to drive an on-board amplifier, which means that their gain claim is bogus, and what they aren't telling you is that the noise floor comes up also. TANSTAAFL. |
#8
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On Mon, 3 Nov 2003 16:40:59 -0500, "Dave VanHorn"
wrote: "Marc H.Popek" wrote in message ... www.fwt.niat.net This dielectric embedded antennas are smaller than naturally occurs and yet have a net gain More correctly, they CLAIM a gain, relative to isotropic. They? HE (the CTO in fact). American business has a recent history of clown elevation. If the antenna is smaller than a free space antenna, then it looses capture area. Capture area is hardly an issue for even the full size antennas they replace. I would be very interested to know how they recoup that. I suspect these antennas might need some power to drive an on-board amplifier, which means that their gain claim is bogus, and what they aren't telling you is that the noise floor comes up also. TANSTAAFL. Hi Dave, What is more to the matter is unstated issues of efficiency. I will let the claims of 8 fold boons pass (which is marketese from the world of ENRON). Compare these "advantages" of reclaimed volume to the unanswered query of weight (no claims about density are there?). Leftover halloween candy. 73's Richard Clark, KB7QHC |
#9
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Richard Clark wrote:
On Mon, 03 Nov 2003 17:00:58 GMT, "Marc H.Popek" wrote: www.fwt.niat.net This dielectric embedded antennas are smaller than naturally occurs and yet have a net gain Hi Marc, Interesting sentence construction. A cogent question would reveal some perspective: How much would your 13dBi dielectric embedded antennas for TV Channel 2 weigh? 73's Richard Clark, KB7QHC A lot less than they would for the 160 meter ham band. -- Many thanks, Don Lancaster Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 voice: (928)428-4073 email: fax 847-574-1462 Please visit my GURU's LAIR web site at http://www.tinaja.com |
#10
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Funnily enough, there is no decrease in capture area with simple, very small
antennas. This is a difficult conception to get people's brains around. There is only a (but important) decrease in efficiency because radiation resistance decreases faster than the loss resistances incurred in matching the antenna to the receiver. Matching loss resistance increases as the antenna dimensions become smaller. For example, think in terms of the Q and loss resistance of the high inductance coil needed in an antenna tuner. |
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