General-purpose AM-FM synthesizer for 0.1 to 520 MHz or 0.1 to 1040 MHz; low noise and excellent AM, FM modulation characteristics. Compact, low-priced signal generator for use in development, production and servicing; can be tailored to customer requirements by adding options. Keyboard entry and LED display of frequency, modulation and level make it easy to operate. Numerical value and unit can be input in ordinary notation; all the values can be varied in single steps or quasi-continuously with selectable step size. Wide output voltage range, exact level setting in dBm, dBµV, µV or mV. Overvoltage protection and IEC-bus programmability (setting time 40 ms) are standard features. Main improvements as against SMS: Low SSB phase noise. Conversion into any of the four level units at the push of a button. Addition and subtraction of freely selectable level steps In dB. Non-volatile storage of 40 complete device settings. Current device setting is saved in case of AC supply failure. Self-test facility. Frequency. The wide frequency range from 100 kHz to 520 MHz (Models 24 and 26) and from 100 kHz to 1040 MHz (Model 28) covers all the sound broadcasting ranges from medium wave to shortwave to VHF, as well as the frequencies of the main radiotelephony bands and radio services up to the UHF region. The Options SMS-B2 permit frequency range extension of the Models 24 and 26 to 1000 or 1040 MHz. The crystal-controlled frequency is read out on the display with a resolution of 100 Hz. The Reference Oscillator Option SMS-B1 (aging < 1 * 10⁻⁶/year) further enhances the accuracy. A reference frequency input is provided on the rear panel of the signal generator (photograph lower right-hand side). The keys permit easy channel stepping with any desired step size. The output signal features low spurious deviation, only 3 Hz (CCITT) or 15 Hz (30 Hz to 20 kHz). The SSB noise 20 kHz from the carrier at a test bandwidth of 1 Hz is between -120 and -126 dBc depending on the frequency. It is -145 dBc at 1 MHz from the carrier. Modulation. The SMS 2 is suitable for all types of modulation: AM up to m - 95% and FM up to deviation = 125 kHz are possible with the aid of the internal modulation generator (400 or 1000 Hz) or an external signal. Modulation frequency and modulation depth or frequency deviation can be entered via a keyboard and are read out on a 3-digit display with 0.05/0.5% and 50 Hz/500 Hz/1 kHz resolution. The maximum frequency deviation of 125 kHz is available over the entire frequency range. The high resolution of the frequency deviation of 50 Hz is helpful when testing transceivers. In addition to AM and FM, the SMS2 offers the following types of modulation: AM + FM together frequency-shift keying for data transmission (FSK) external level control (ALC).