Sencore FC45 Frequency counter
With the increased popularity of personal communications, the need for accurate frequency measurements is becoming more common to many shops. Communications equipment such as CB and land-mobile transceivers, as well as AM, FM, and TV transmitters require frequency measurements within FCC specifications.
The design and troubleshooting of digital equipment often requires adjustment of reference oscillators for proper operation. A frequency Counter
also simplifies the troubleshooting of many non-digital circuits such as TV color-burst, horizontal and vertical oscillators. In addition, a high sensitivity Counter
allows alignment of other test equipment such as RF generators or function generators.
The large (.5”) 8-digit display of the FC45
allows easy reading of any frequency from the audio range through VHF. The display includes automatic decimal placement and “Hz”, “MHz” indicators for direct frequency measurements.
includes a built-in 10:1 prescaler for measurements to 230 MHz. An optional external prescaler extends the measuring capability to 600 MHz with high sensitivity. All of the measurements are accurate to 1 part per million (ppm) or .0001% to exceed FCC specifications for communications work. The crystal-controlled timebase is oven controlled to maintain this accuracy over a wide range of operating temperatures.
offers two inputs. The high-sensitivity 1 Megohm input is usable through the entire frequency measurement range of the FC45
, The second 50-0hm input provides a dummy load rated at 12 Watts RF. This dummy load is diode protected against overloads with backup fuse protection to protect the diodes.
A choice of a .1 second or 1 second timebase allows the choice of a fast 10 updates per second, or increased resolution. Sen core’s exclusive crystal check mode allows most crystals (including CB, VHF, and UHF) to be checked by simply plugging the crystal into the FC45’s front panel-socket.
Finally, a choice of 12 VDC or 117 VAC operation offers true versatility for bench or portable testing.
Service and User Manual
5.66 Mbytes (5939647 Bytes)
02 October 1977
Scanned document, all readable.
17 May 2020
SAFETY WARNINGS ... inside Front Cover
Features ... 4
Specifications ... 4
Controls ... 6
Power Connections ... 8
Fuse Replacement . ... 8
Selecting Proper Input ... 9
50 Ohm Input ... 9
1 Meg Input ... 10
Crystal Check ... 10
Selecting Frequency Range ... 11
Selecting Read Rate ... 11
Using PR47 UHF Prescaler ... 12
Signal Connections ... 12
Supplied Counter Probe
1 Meg Input, Direct Connection ... 13
1 Meg Input, Isolated Connection ... 13
50 Ohm Input, Direct Connection ... 13
50 Ohm Input, Isolated Connection ... 13
10:1 Resistive Isolation ... 13
PL207 RF Pick-Up Loop ... 14
Special Digital Applications ... 14
Counting "Noisy" Audio Signals ... 15
Modulated Waveforms ... 16
Counting "Noisy” Signals ... 16
Crossover Distortion ... 16
Signals with Ripple ... 17
Digital Noise ... 17
Pulse Ringing ... 17
Theory of Operation ... 19
Functional Block Diagram ... 19
Accuracy ... 21
Access/Disassembly ... 21
Recalibration Procedures ... 22
External Reference Drive Modification ... 23
SERVICE AND WARRANTY ... Inside Back Cover