Most electronics technicians are finding more and more
need for a high accuracy digital frequency counter.
Communications shops and commercial broadcast stations
need both a wide frequency range and high accuracy
in their frequency counters to meet the FCC
requirements for accurate measurements of various
transmitter frequencies. Service technicians find that
a frequency counter is a valuable piece of test equipment
for troubleshooting the digital circuits found in
UHF and VHF television tuners and the modern digital
FM receivers. Other applications (like video tape
recorder, medical equipment, and industrial maintenance)
require frequency counters for many tests and
The FC51 offers both a wide input frequency range
and high accuracy for work in any of these applications
where the signal is between 10 Hz and 1000 MHz.
Extra features, like all pushbutton operation and automatic
selection of prescalers, are normally found only
on frequency counters costing much more than the
FC51. A review of the following section will cover
these special features and explain how they simplify
the operation of the FC51 and offer versatility not
usually found in a frequency counter in this price
The FC51 1 GHz Frequency Counter allows direct
readings of all frequencies from 10 Hz through 1 GHz
with accuracies that exceed the FCC specifications
for all communications work up to 1 GHz. The metal
case of the FC51, along with internal RF shielding,
provides interference-free measurements in practically
any type of RF field.
The large (.5”) 8 -digit display allows direct readings
with automatic placement of the decimal. Special
indicator lights show whether the counter is measuring
"Hz" or “MHz”, and an overflow indicator indicates
that a reading requires more than the full 8
digits of readout.
The FC51 features large, comfort-sized pushbuttons
for ease of operation. These buttons select the desired
input jack, read rate, and frequency range. Three
inputs are available. The first is a fuse-protected 50
Ohm termination for proper reading of high frequency
signals. The 50 Ohm termination prevents cable
ringing which could cause inaccurate readings.
The second input is a high sensitivity input with 1 Megohm
loading to allow direct connections to lower frequency
circuits. This input is controlled by a frontpanel
sensitivity control which allows many noisy signals
to be measured which normally will produce erratic
readings on a high sensitivity counter.
The sensitivities of both of these inputs have been designed
for fast signal tracing in most applications. If
additional sensitivity is required for special applications,
the optional WBA52 1 MHz through 1 GHz
Wideband Amplifier provides an additional 30 dB of
input gain. The WBA52 is powered from the accessory
jack on the front of the FC51.
The third input is Sencore’s exclusive crystal check
which allows any crystal to be tested by simply inserting
it into the special front panel test socket.
Two read rates give a choice of fast updates or maximum
resolution, depending on the type of signal you
want to measure. Four different frequency range buttons
provide the best resolution for any measurement.
Two built-in prescalers extend both the high and low
frequency capabilities of the FC51. The first prescaler
allows frequencies from 100 MHz to 1 GHz to
be measured and the second “audio prescaler” provides
additional digits of resolution when measuring
frequencies below 20 KHz. Both prescaled options
provide automatic decimal placement for direct readings.
The high accuracy timebase oscillator is built into a
proportionally-controlled oven to assure the highest
accuracy possible over a wide range of ambient temperatures.
The entire oven and oscillator is contained
in a single plug-in module to allow the option of exchanging
the module with one that is freshly calibrated
so that it is not necessary to return the entire counter
for accuracy calibration.
Finally, the FC51 offers a choice of 110-120 VAC
line operation or 12 VDC operation for versatility of
use in bench or portable testing. Input connections
are made with the supplied counter probe, pickup
loop or adjustable antenna.