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

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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. (?)

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

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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.

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.

"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