DSI 3550 Frequency Counter 50Hz-550MHz with Antenna Gate Control

DSI 3550 Frequency Counter 50Hz-550MHz with Antenna Gate Control

The DSI 3550 is a compact benchtop frequency counter covering two overlapping measurement ranges: 50Hz to 55MHz via direct input and 30MHz to 550MHz via its built-in telescoping antenna. A rotary gate-time selector on the front panel allows the operator to choose between 0.1-second and 1-second gate intervals, giving flexibility for fast sweeps or more stable readings. The unit displays frequency on a red LED numeric readout and includes a Gate indicator light on the front panel.

Specifications & What's Included

• Manufacturer: DSI
• Model: 3550
• Type: Frequency Counter
• Frequency Range (direct input): 50Hz – 55MHz
• Frequency Range (antenna): 30MHz – 550MHz
• Gate Time: 0.1 Sec / 1 Sec (rotary selector)
• Display: Red LED numeric readout
• Front panel: DSI 3550 label, LED display, Gate indicator light, gate-time selector knob
• Rear panel: Two coax/BNC-style input connectors, small auxiliary jack, power/sensitivity knob
• Form factor: Benchtop/desktop, black textured enclosure
• Includes: Telescoping whip antenna (detaches from rear panel)

Applications

The DSI 3550 is a general-purpose frequency counter suited for measuring RF signals in the HF through VHF range. Counters of this type are used by amateur radio operators, two-way radio technicians, and electronics hobbyists to identify transmitter frequencies, verify oscillator output, and check channel assignments on radios and wireless equipment. The 30MHz–550MHz antenna range makes it practical for monitoring or checking VHF and low-UHF transmitters — including FM broadcast, public safety, and land mobile radio — without a direct connection to the signal source. The dual-range design and compact desktop form factor were common in budget-oriented bench and field frequency counters from the 1980s and early 1990s.