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30 MHz Frequency Counter (MHSZ BRK 1978) Andrew Sümegi (HA2ERZ)

This is a simple TTL lab frequency counter which I built decades ago. At that time I was a young student and short on funds and commercial laboratory instruments were totally out of my reach so I had to build my own. This frequency counter has been designed at Hungarian Defense Sport Association (MHSZ) in 1978, and built any for next several years. Today it would probably not make sense to build this type of instrument as there are commercial units for very reasonable prices and it would be more productive to just work to earn the needed money. The instrument which I built has been destroyed completely by an earthquake in 1985. Sometime last year I found an other unused circuit board in my collection and tried reverse engineering the schematic. As you can see, this schematic contains simple asynchronous counter/divider ICs type Texas Instruments SN7490. You can read all about this here: R. M. Marston: Modern TTL Circuits Manual, and you can replace them with 74LS90. This circuit diagram dioes not shows the display unit. It is not the PCB. Originally we used six Nixie-tubes with SN74141, but you can use a LED display too if you want it.

Specs:  Maximum



SN74LS196 30 MHz minimum (40 MHz typical). With SN74S196 measuring is possible up to 100 MHz. Timebase: 1 MHz crystal oscillator

Display resolution: 0,1 kHz

RMS sine wave sensitivity: cca. 0,1 V

Power: +5V DC

Display: 6-digits BCD (not included)

This is a similar instrument by HP





30 MHz Frequency Counter (MHSZ BRK 1978)  
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