Home › Forums › temp › Part15 FM, another approach to attempting to “verify” compliance. › Re: OK on FM only
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……Do you think that the receiving antenna and line could give the same problems for accurate FM measurements that I experienced on AM? Your S meter idea may be useful for “ballpark” measurements if somehow it could be calibrated with a known field or the antenna characteristics were known. For example we would have to know how the antenna converts the uV/m field strength to uV at the receiver input. Maybe if the field strength of a broadcast station were known with some accuracy at a certain location this could serve as a rough calibration. Any thoughts on this?
You may already know this, if so just bang me in the head. For FCC and other compliance measurements, calibrated antennas are employed with an accompaning antenna correction factors (ACF) in dB. The antennas are calibrated against a reference antenna on an open area test site.
The antennas can be adjustable dipoles, log periodics, conical, etc.. The FCC has long prefered dipoles although under certain circumstances they will allow other types of antennas as long as one can document and corrolate to a dipole.
So measuremets of field strength are made by measuring the energy at a specified distance impinging on the antenna, the ACF +/- in dB and cable loss are factored into the final measurement. A field strength meter (FSM) or spectrum analyzer is employed.
So to answer your question: yes, a receiving antenna can adversly effect the measurement. A gain antenna like a yagi would result in a higher reading.