Really? Here is a comprehensive "datasheet"
describing the handheld Rhode & Schwarz FSH6
Spectrum Analyzer. Searching with Google, I couldn't find any information on "R&S FHS6
's" that you claim to have. But, congratulations on having two
of whatever it is that you DO have.
If I were looking to measure spectrum occupancy or signal density in both the AM radio band (550kHz to 1200kHz) and the commercial FM band (88MHz to 108MHz) in fringe reception areas, then I would connect an antenna
to the spectrum analyzer, with or without a suitable pre-amplifier. You could use a ferrite loop-stick (un-tuned) antenna to sample the AM spectrum... or perhaps a largish flat coil of wire to create a small magnetic loop antenna. Either approach will be somewhat directional however. Perhaps a mono-pole vertical antenna will suffice for the FM spectrum, but these are sensitive to polarization. I would not attempt to measure both the AM and FM bands simultaneously, and certainly not with the same antenna..
It is not immediately clear to me that you actually know how a Rohde & Schwarz spectrum analyzer works. Maybe this datasheet
(in English) will help. Perhaps that isn't necessary in your line of work.
Most spectrum analyzer input(s) are quite sensitive to damage from excessively strong signals. The low-noise mixer, to which is applied the input signal(s), is easily damaged. Be careful to measure (and/or attenuate) unknown signals before connecting them to the spectrum analyzer input(s).
And it is also not obvious that you have any idea how an AM/FM radio works, but feel free to correct me if am wrong about any of the above.
Virtually ALL AM/FM radios (and any other serious radio beyond crystal sets and ancient TRF models) operate on the superheterodyne
principal. This means they all mix (heterodyne) the antenna signal (possibly amplified with a tuned RF amplifier) with a local oscillator (LO) signal to obtain a single range (or spectrum) of sum and difference frequencies. Both the sum and difference frequency spectrum equally represent the frequency spectrum of the received signal, although typically only the difference frequency spectrum is amplified and later demodulated to an audio frequency spectrum. Usually, the difference frequency spectral range is amplified by an intermediate frequency
or IF RF amplifier, tuned to accept whatever modulation bandwidth is expected from the signal source. Note that the spectrum band of frequencies is different for each transmitting station, but by changing the local oscillator (LO) frequency, each station's spectrum can be made to fall within the IF amplifier bandwidth. Thus the IF amplifier is tuned to amplify a particular portion of the radio spectrum whose information content, regardless of modulation, is a duplicate of the original transmitted spectrum.
For the sake of completeness, I should mention that most communications receivers of newer design use direct conversion instead of superheterodyne conversion, and digital sampling of the antenna signal. With direct conversion, the local oscillator is tuned to the carrier frequency (or a replication of the original carrier frequency) and the difference spectrum is processed as a pseudo-audio signal. With in-phase and quadruture-phase demodulation, a pair of signals is created that can be used for a spectral display, much like a spectrum analyzer but with limited frequency range and functionality.
It is very efficient to design an RF amplifier that need respond to only a fixed and relatively narrow band of frequencies. Those little "cans" you see scattered about the innards of your AM/FM radio are shields for the LC tuned transformers that are connected to the inputs and outputs of the IF amplifiers. Because of the huge difference in frequencies used between the AM and FM bands, the IF RF amplifiers for each of these bands are also different and the intermediate frequency provided by the local oscillator is also different. Bear in mind that there is also a LOT of very active spectrum space between the largest AM broadcast frequency and the lowest FM broadcast frequency. Your AM/FM receiver is designed to ignore this spectrum.
Much of this "ignored" spectrum space, up to about 30MHz or so, is usually described as the the high-frequency (HF) "shortwave band" and is accessible by superheterodyne communication receivers. Some communication receivers have more than one intermediate frequency and are called dual-conversion receivers. The higher received frequencies, as selected by a local oscillator, are amplified in the first IF amplifier and then that output is mixed with a second local oscillator to create a second IF band of frequencies at a lower intermediate frequency.
The Rohde & Schwarz spectrum analyzer operates much like a communications radio, except the tunable local oscillator (LO) In a spectrum analyzer, the LO frequency, is not used to select a particular band of frequencies. The LO frequency is swept from a lower frequency to a higher frequency so the output at any instant represents a "snapshot" of the radio frequency energy present in a narrow, usually operator-adjustable, frequency band surrounding the local oscillator frequency.
my aim is to monitor the AM/FM frequency spectrum in poor reception areas.
Gee, us po' folk do this all the time when we are out traveling in the boondocks. We tune the car radio from one end of the band to the other hoping to hear a broadcast radio station. Hmmmm. Nothing but static noise on AM. FM is quieter, but still no stations are heard. Maybe we are in a radio "quiet zone". The nearest one to me is near Greenbank, WVA. My wife and I have never left the broad interstate trail to visit the National Radio Telescope, but I have, on my own, found some relatively quiet places while traveling in the great American West. Such "radio quiet" places are difficult to find, especially for AM signals at night: AM covers a LOT more distance at night than FM.