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FM Transmitter in a hot air balloon?
So I was doing some reading and one article mentioned that a group
mounted an FM transmitter on a hot air balloon. I was also researching on the methods used by the FCC to measured field strengths. So how does one go about measuring field strength levels if a company somewhere, somehow, sometime decides to mount their transmitter on a hot air balloon to avoid building a tower? Would the FCC procedures still be valid? I wondering how the field strength tester would go mobile 30 meters from the radial or measurement point if the transmitter is changing position constantly. |
#2
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FM Transmitter in a hot air balloon?
Ron J wrote:
So I was doing some reading and one article mentioned that a group mounted an FM transmitter on a hot air balloon. I was also researching on the methods used by the FCC to measured field strengths. So how does one go about measuring field strength levels if a company somewhere, somehow, sometime decides to mount their transmitter on a hot air balloon to avoid building a tower? Would the FCC procedures still be valid? I wondering how the field strength tester would go mobile 30 meters from the radial or measurement point if the transmitter is changing position constantly. Well, since it wouldn't conform to any of the standard charts, they would have to use a real field strength meter. -- Jim Pennino Remove .spam.sux to reply. |
#3
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FM Transmitter in a hot air balloon?
On Jan 24, 6:55 pm, wrote:
Well, since it wouldn't conform to any of the standard charts, they would have to use a real field strength meter. -- Jim Pennino Real field strength meters? Like these: http://www.pi-usa.com/products.htm . I thought field strength measurements require real field strength meters. (?) |
#4
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FM Transmitter in a hot air balloon?
Ron J wrote:
On Jan 24, 6:55 pm, wrote: Well, since it wouldn't conform to any of the standard charts, they would have to use a real field strength meter. -- Jim Pennino Real field strength meters? Like these: http://www.pi-usa.com/products.htm . I thought field strength measurements require real field strength meters. (?) I didn't bother to read the ad, but if it can be calibrated to NIST standards, yes. You can also do it with a spectrum analyzer and a calibrated antenna. -- Jim Pennino Remove .spam.sux to reply. |
#5
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FM Transmitter in a hot air balloon?
On Jan 25, 12:35 pm, wrote:
I didn't bother to read the ad, but if it can be calibrated to NIST standards, yes. You can also do it with a spectrum analyzer and a calibrated antenna. -- Jim Pennino I think my school will lend me a spectrum analyzer, but not sure if I can get access to a calibrated antenna. One of my school projects involves in measuring the field strength of a low power FM transmitter mounted in a "smart" flyer. Really the flyer is just a toy helicopter fitted with sensors and given a "brain" by the computer science folks. The idea behind it is that it's suppose to monitor local traffic conditions using a video feed and then it will broadcast some pre-recorded messages via the FM transmitter warning on-coming drivers of potential road blocks. However, the drivers will need to tune their radio station to a specified frequency. I'm not involved with the frequency stuff, so I don't know how it's going to play out with the feds. Anyway, I'm supposed to determine the range of the FM transmitter by measuring the field strength. But I'm reading some propagation text like Les Barclay's Propogation of Radio Waves and found out that field strength varies with antenna height, distance from receiver and transmitter, and also the landscape. I've also scoped out some FCC procedures for measuring radio broadcast, and they have some 50,50 curves that I don't understand too much. But the FCC assumes that the transmitter is fixed. In this thing, the transmitter is moving around, so I'm having a difficult time figuring out how to come up with some transmission range diagram. The intent of my original question is to find out how someone would measure it. I'm sure the balloon folks had the same issue. |
#6
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FM Transmitter in a hot air balloon?
Ron J wrote:
On Jan 25, 12:35 pm, wrote: I didn't bother to read the ad, but if it can be calibrated to NIST standards, yes. You can also do it with a spectrum analyzer and a calibrated antenna. -- Jim Pennino I think my school will lend me a spectrum analyzer, but not sure if I can get access to a calibrated antenna. One of my school projects involves in measuring the field strength of a low power FM transmitter mounted in a "smart" flyer. Really the flyer is just a toy helicopter fitted with sensors and given a "brain" by the computer science folks. The idea behind it is that it's suppose to monitor local traffic conditions using a video feed and then it will broadcast some pre-recorded messages via the FM transmitter warning on-coming drivers of potential road blocks. However, the drivers will need to tune their radio station to a specified frequency. I'm not involved with the frequency stuff, so I don't know how it's going to play out with the feds. Anyway, I'm supposed to determine the range of the FM transmitter by measuring the field strength. But I'm reading some propagation text like Les Barclay's Propogation of Radio Waves and found out that field strength varies with antenna height, distance from receiver and transmitter, and also the landscape. I've also scoped out some FCC procedures for measuring radio broadcast, and they have some 50,50 curves that I don't understand too much. But the FCC assumes that the transmitter is fixed. In this thing, the transmitter is moving around, so I'm having a difficult time figuring out how to come up with some transmission range diagram. The intent of my original question is to find out how someone would measure it. I'm sure the balloon folks had the same issue. "Real" calibrated antennas that meet FCC requirements with calibration traceable to NIST aren't cheap. Though if all you are doing is trying to estimate range and don't have to send traceable data to the FCC, you could get a good idea by using antenna modeling software and modeling the antenna in free space. -- Jim Pennino Remove .spam.sux to reply. |
#7
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FM Transmitter in a hot air balloon?
"Ron J" wrote:
The idea behind it is that it's suppose to monitor local traffic conditions using a video feed and then it will broadcast some pre-recorded messages via the FM transmitter warning on- coming drivers of potential road blocks. If this application is a real project, and intended for the US, and you need it to "broadcast" to FM receivers over an area that would be fairly useful for this purpose, then a station license will be needed from the FCC. Unlicensed transmitters in the 88-108 MHz band are restricted under 47 CFR Part 15 to radiated field strengths not exceeding 250 µV/m at a distance of three meters in all directions from the transmit antenna. The transmit antenna needs to radiate only ~18.8 nanowatts in order to generate that field. FCC OET Bulletin 63 is a good resource for this situation http://www.fcc.gov/Bureaus/Engineeri...3/oet63rev.pdf . Anyway, I'm supposed to determine the range of the FM transmitter by measuring the field strength. The propagation paths for these circumstances will be line-of-sight, so except for reflections, received field strength will be inversely proportional to the distance from the transmit antenna. A system operating legally under Part 15 would produce a field of about 2 µV/m at a distance of about 1,400 feet. So if the airborne tx system elevation was 500 feet, its ability to cover a significant area on the ground with useful signal strengths will be reduced. Hopefully this background information will be useful. RF http://rfry.org |
#8
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FM Transmitter in a hot air balloon?
Ron J wrote:
So I was doing some reading and one article mentioned that a group mounted an FM transmitter on a hot air balloon. I was also researching on the methods used by the FCC to measured field strengths. So how does one go about measuring field strength levels if a company somewhere, somehow, sometime decides to mount their transmitter on a hot air balloon to avoid building a tower? Because the communications are likely to be line of sight, you could use inverse square law equations to predict the signal strength. Would the FCC procedures still be valid? I wondering how the field strength tester would go mobile 30 meters from the radial or measurement point if the transmitter is changing position constantly. FCC test procedures? How about FAA procedures? Keep in mind that with balloon launches such as this group does, there are notices issued warning aviators and air traffic controllers about it's existence. If you poke something any higher than 700 or 1200 feet in the air (depending where you are), you're in controlled airspace. You must notify the local flight service station and provide position information IN ADVANCE. Jake Brodsky, AB3A PP-ASEL-IA, Cessna Cardinal N30946 based KFME |
#9
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FM Transmitter in a hot air balloon?
Jake Brodsky ) writes:
Ron J wrote: So I was doing some reading and one article mentioned that a group mounted an FM transmitter on a hot air balloon. I was also researching on the methods used by the FCC to measured field strengths. So how does one go about measuring field strength levels if a company somewhere, somehow, sometime decides to mount their transmitter on a hot air balloon to avoid building a tower? Because the communications are likely to be line of sight, you could use inverse square law equations to predict the signal strength. I was reading the problem as "since the balloon is moving, how can you even fix on a pattern" A lot of that isn't so much about field strength as pattern. They want that controlled. And that's arrangeable when the antenna is fixed. But if the antenna is moving about, then the pattern will change as it moves, so you can't guarantee that it won't interfere with that station in the next town over, while a fixed antenna would allow some sort of directionality to provide a shadow in that direction. Reminds me of people using 2M FM in the early seventies, from small airplanes. They had no problem with a handie-talkie's low power output, they had all kinds of problems with not being able to control it so transmitting on a popular frequency would trigger a bunch of repeaters at one time. Michael VE2BVW |
#10
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FM Transmitter in a hot air balloon?
On Jan 25, 8:14 pm, Jake Brodsky wrote: Ron J wrote: So I was doing some reading and one article mentioned that a group mounted anFMtransmitteron ahotairballoon. I was also researching on the methods used by the FCC to measured field strengths. So how does one go about measuring field strength levels if a company somewhere, somehow, sometime decides to mount theirtransmitteron ahotair balloonto avoid building a tower? Because the communications are likely to be line of sight, you could use inverse square law equations to predict the signal strength. Actually, no, inverse square (free space) will underestimate the received signal strength. There's also a "height above the ground" factor that would need to be taken into account for UHF and VHF links, because the ground reflections are significant on both ends of the link. A program called Radio Mobile (google for it) can do the modeling over your terrain. Or, you can probably find one of the quick approximations for uniform terrain. The usual model is called Longley-Rice, but Bullington has a quick approximation. |
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