UHF-MOD AM/FM Modulation

The AM/FM modulation option allows the direct measurement of sidebands in dynamic AM (amplitude modulation) and FM (frequency modulation) schemes. This option helps the user to precisely measure the periodic variations in the frequency or the amplitude in the first sideband of the carrier frequency.

UHF-MOD Key Features

• Two independent AM/FM modulation units
• Amplitude modulation and demodulation (simultaneous)
• Frequency modulation and demodulation (simultaneous),
  for narrow-band specs
• Dual-modulator (signal output) configuration
• Harmonic sideband analysis (2 sidebands)
• Sideband separation (single-sided modulation)

UHF-MOD Upgrade and Compatibility

• Option upgradeable in the field
• Requires UHF-MF Multi-frequency option
• Compatible with all other UHF options

UHF-MOD Functional Diagram

UHF-MOD Amplitude Modulation

s(t) = [ A_c + A_m * sin(ω_mt) ] * sin(ω_ct)

In AM the amplitude of a carrier signal is periodically changing (modulated). In most applications this modulation is small and is therefore subject to noise. The purpose of recovering an AM signal with a lock-in amplifier is to take advantage of its steep filters and time integration to extract the signals of interest. As the AM spectrum consists of 3 bands, the UHF-MOD uses 3 demodulators to demodulate all 3 bands simultaneously providing a best-in-class signal recovery performance. Simultaneous amplitude modulation and demodulation is supported and can be entirely controlled from the graphical user interface of the UHF Instrument. The generation of AM signals is useful for stimulus generation in the application, but can also be utilized for system testing purposes.

UHF-MOD Frequency Modulation

s(t) = sin[ ω_ct + ω_p/ω_m * sin(ω_mt) ]

In FM the frequency of a carrier signal is periodically changing (modulated). As the modulation is often a small signal and therefore subject to noise, the demodulation with a lock-in amplifier can be advantageous thanks to its configurable filtering. The UHF Instrument is capable to demodulate a signal of interest at several frequencies simultaneously, and the UHF-MOD option provides the FM demodulation at the carrier frequency and a selectable pair of sidebands (ω_c ± n * ω_m). For narrow-band operation, the peak frequency deviation and the modulation frequency shall satisfy the relation ω_p/ω_m << 1 , but the UHF-MOD option operates also above this limit with a decreasing accuracy, i.e. ω_p/ω_m < 2 .

UHF-MOD User Benefits

• Single-box solution for bimodal, multi-modal measurement challenges
• Tandem demodulation implemented using 1 lock-in amplifier (instead of 2), no intermediate signal conversion
• Easy to use: less cabling compared to tandem
• Phase coherence between carrier and modulation: allows sideband phase measurement (not possible with tandem demodulation)
• Modulation frequency may be arbitrarily big compared to carrier frequency
• Compatibility with UHF-PID option allows that carrier and modulation frequency can be derived from a high-performance PLL
• Accounts for system asymmetries by separating upper and lower sideband

UHF-MOD Specifications