-2. The John Fluke Model 7220A is a nine-digit portable, bench-type Counter that provides wide-range frequency measurement capability up to 1300 MHz. There are two input channels. The ac-coupled Channel A input allows frequency measurements from 10 Hz to 125 MHz with I Megohm input impedance. The Channel B input allows prescaled frequency measurements of continuous wave or burst signals from I00 MHz to 1300 MHz with 50 ohm input impedance. Channel A signal conditioning includes a X 10 fixed attenuator and a X10 variable attenuator. For low frequency measurements, a 100 kHz low-pass filter may be selected. Four standard resolution .settings and gate times may be selected that allow resolution in decade steps from 100 Hz to 0.1 Hz. Four additional resolution settings (up to .0001 Hz) are available when the Resolution Multiplier Option-351 is installed. 1-3. Measurements are displayed on a nine-digit LED display. Three LED annunciators indicate gate time, measurement overflow, and if optional oven time base is receiving power. The 7220A may be operated with the standard 10 MHz timebase, an optional TCXO (Temperature Compensated Crystal Oscillator) time base, or either of two optional low power oven time bases. A self check mode applies the time base signal to the internal counters, thus providing a check for most of the 7220A internal circuitry. 1-4. The 7220A is enclosed in a PTI (Portable Test Instrument) case which includes an inner metal lining for RF1 shielding. The counter may be operated at switch selectable line voltages of 100V, 120V, 220V or 240V at 47-63 Hz, or with an optional battery pack. 1-5. OPTIONS AND ACCESSORIES l-6. When the Battery Pack Option -0I0 is installed along with one of the optional oven time bases, high measurement accuracy is provided with portable convenience. When the Digital Interface Option -521 is installed in the 7220A, serial BCD data is available at a rear panel output. Option -521 also allows the counter to operate directly into a Fluke 2020A, 2021 A, or 2030A Printer (with Option -004 installed in the Printer). When Option »521 is installed in the 7220A, and it is used with a Fluke I120A Translator with Option -522 installed (in the 1120A), the 7220A is compatible with the IEEE-488 Bus. All of the options are described in detail in Section 6. Tables 1-1 and 1-2 list the available options and accessories for the 7220A.