Note
QST, Feb 1976. p 128.
intro date unknown, but before 1976.
YC-601B
QST, Jan 1979, p. 193.
intro date unknown.
QST, Aug 1976, p. 88.
QST, Feb 1977, p. 163.
The Yaesu YC-601 series consists of solid-state companion digital display accessories designed primarily to provide direct operating frequency readouts for Yaesu's classic hybrid transceiver lines. They are specifically tailored for interface with the FT-101/277 and FTdx401/505 (or FTdx401/501) series transceivers, as well as associated external VFOs (like the FV-101 and FV-401) and receivers (like the FR-101).
Both models share the same physical footprint, feature a multi-voltage internal AC power transformer, and utilize a 6-digit display that provides a standard resolution down to 100 Hz. They read the transceiver's injected VFO signal and apply a fixed offset calculation to present the exact operating frequency.
Key Differences Between the YC-601 and YC-601B
While they look similar on the bench, the YC-601B is a substantial hardware refinement over the original YC-601, introducing independent test equipment capabilities alongside layout changes.
1. Functional Capabilities: Dedicated Display vs. General-Purpose Counter
YC-601: Functions strictly as an external digital frequency display for a connected transceiver. It translates the VFO's input frequency band to match the transceiver's band position. The 601 use a blue-green vacuum fluorescent display.
YC-601B: Functions as a dual-purpose unit. It includes a front-panel MODE switch to toggle between standard BAND mode (transceiver display) and COUNTER mode. In counter mode, it functions as an independent laboratory frequency counter covering a wide range from 100 Hz to 35 MHz. The 601B uses red LED display.
2. Resolution and Gate Times
YC-601: Uses a fixed gate time of 0.1 seconds, giving it a standard resolution of 100 Hz.
YC-601B: Introduces a GATE TIME toggle switch on the front panel. When used in Counter mode, switching the gate time from 0.1 seconds to 1.0 second increases the counter's resolution tenfold—allowing it to read down to 10 Hz (displaying 5 digits past the MHz decimal point).
3. Front Panel Controls & Inputs
The front panel was completely redesigned for the "B" variant to accommodate its new counter functionality:
Input Terminal: The YC-601B adds a prominent front-panel BNC input jack labeled INPUT to hook up test probes or the supplied alligator clip cable for frequency sampling. The original YC-601 has no front-panel inputs.
New Switching: The YC-601B adds a HOLD switch (to freeze the current frequency readout on the display), a MODE (BAND/COUNTER) switch, and a GATE TIME (1s / 0.1s) switch.
Calibrate Knob Relocation: On the original YC-601, the CALIB (calibration) knob is located to the right of the display window. On the YC-601B, the CALIB knob is moved to the far left, directly above the power switch, to free up space for the counter controls and BNC jack.
4. Out-of-Band Behavior
YC-601: Features a built-in out-of-band warning system that automatically flickers the display if the transceiver's VFO frequency wanders outside of its intended 500 kHz coverage.
YC-601B: Relies instead on the manual counter constraints and the explicit position of the BAND/AUX switch matching the radio equipment.
Specifications
– Display digits: 6
– Clock frequency: 1.31072 MHz
– Ambient temperature: 0–40ºC
– Power requirements: 100/110/117/200/220/234 VAC, 50/60 Hz
– Power consumption: 7 VA nominal (10 VA for YC-601)
– Frequency coverage: Amateur bands within the range 1.5000 MHz to 29.9999 MHz
– Input frequency: 8700 kHz to 9200 kHz @100 mV RMS
– Gate time: 0.1 sec.
– Display time: 0.2 sec.
YC-601B Frequency Counter
– Frequency range: 100 Hz–35 MHz
– Input requirements:
100 Hz: 180 mV
1 kHz to 10 MHz: 30 mV
35 MHz: 90 mV
– Maximum input voltage: DC: 100 Volts, AC: 2 Volts RMS
– Input resistance: 1 MΩ
– Input capacitance: Less than 30 pf.
– Gate time: 0.1 sec. for 100 Hz resolution
– 1 sec. for 10 Hz resolution
– Clock accuracy: ±20 PPM at 25ºC
YC-601 and YC-601B
WARNING: DO NOT EXCEED input voltages: DC: 100 Volts, AC: 2 Volts RMS
