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Home / Electronics / Equipment / Panel Mounting Radio Frequency Counter |
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Radio Frequency Counter |
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This very tiny frequency counter was built to fit inside the front panel
of a radio tranceiver. It now occupies pride of place in the front panel of my HF Receiver, alongside my panel mounting clock.
One of the switches is used to switch the counter on and off, the other
sets the display resolution. The two choices for display resolution are
1Hz, which will read one measurement per second, or 10Hz, which will read
10 measurements per second. The decimal points are automatically displayed
in the correct position to indicate MHz and KHz markers. The counter uses
CMOS 74HC chips. Like the matching clock, the counter uses switching of
the display LEDs instead of a real voltage regulator. Unlike the clock,
it didn't undergo a meltdown...
The counter is shown in the photo (above left) with the matching panel mounting clock in
the background, measuring a frequency of 384 KHz from the timing chain
of the clock.
The counter is encased in single-sided unetched PCB material, soldered
together on the inside into a box shape. The nuts on the toggle switches
are used to secure the counter inside the case of a radio tranceiver.
I actually built this counter during my finals at university, it was a
good break.
At the left of the counter a coil can be seen - this is input filtering of the supply voltage, the idea being to prevent spurious signals from the frequency counter's timing chain from entering the host radio receiver.
The circuit is built on a triple-decker vero-board arrangement (see right). Compact, but difficult to make repairs! On the left note the coil for supply line filtering. The bolts protruding from the rear circuit board are used to fix the assembly in it's PCB-material case, although its such a tight fit they're scarcely needed!
CLICK HERE for an Adobe Acrobat .pdf file containing the three pages of circuit diagrams.
Page 1: Counting chain, display decoders and 7-segment displays.
Page 2: Timing chain and logic.
Page 3: The placement of the chips on the boards, and pinouts.