No affordable field strength meter is going to tell you any kind of reliable measure of uV/m. Plus an anechoic radio chamber.
under "Any" it says 200 uV/m @3m, . is that means 3 minutes of continuous transmission?
You've figured out now that this is a measure of signal strength, yes? 200uV/m measured at 3meters distance?
This part I think excludes you from altering the transmitter in any way, including the antenna:
In order to prevent such interference problems, each Part 15 transmitter must be
designed to ensure that no type of antenna can be used with it other than the one used
to demonstrate compliance with the technical standards. This means that Part 15
transmitters must have permanently attached antennas, or detachable antennas with
unique connectors. A "unique connector" is one that is not of a standard type found in
electronic supply stores.
It is recognized that suppliers of Part 15 transmitters often want their customers to be
able to replace an antenna if it should break. With this in mind, Part 15 allows
transmitters to be designed so that the user can replace a broken antenna. When this
is done, the replacement antenna must be electrically identical to the antenna that was
used to obtain FCC authorization for the transmitter. The replacement antenna also
must include the unique connector described above to ensure it is used with the proper
What you are reading is really more for an EE and GROL license holder who is designing a Part 15 transmitter.
What is it you are trying to do? Digikey, Mouser, Jameco, Seeed Studio, Sparkfun, Amazon, and others sell RF modules. Presumably, if they weren't legal, they'd have been stopped by now. As far as FCC certification, those are unlicensed bands as long as they stay within the confines of the regulations, so I don't think the FCC certifies them.
Since wireless LANs, Bluetooth, and ZigBee have been introduced, much of the design effort within the unlicensed spectrum in the U.S. has been focused on the 2.4-GHz band. But other unlicensed bands that the Federal Communications Commission (FCC) set aside for industrial, science and medical (ISM) applications also have a lot to offer design engineers who need wireless links for short-range audio and video transmission, as well as a variety of remote control, metering and sensing applications.
FCC regulations for the 915-MHz ISM band, for example, place no restrictions on type of application or duty cycle. In addition, the power output permitted by the regulations is considerably higher than it is in other portions of the ISM spectrum.
915 MHz is the center frequency of the band bounded by 902 and 928 MHz. Within this band, FCC regulations allow 50 mV/m electrical field strength, at a distance of 3 meters from the transmitting antenna.