I must admin that i never had a frequency counter in my bench. Never understood why…
My KN-Q7A doesn’t have any frequency counter at all so i decided to build a small one for measuring the IF and LO frequencies and provide an indication of where exactly i am transmitting (till i add a DDS VFO)
There are many different designs on the Internet based on AVR and PIC but there is ONE that grabbed my attention. I would consider the easiest to build.
So i grabbed the design of DL4YHF http://www.qsl.net/dl4yhf/freq_counter/freq_counter.html and build it on a perfboard and here you go. I used a 4-digit Common Anode Display 5461BS to reduce the amount of wires.
I have also modified the firmware to add the IF i use 8.467 MHz for CA display (counter_CA_8467IF.hex) In the cost of removing the 4.433619 MHz which could potential be used in the 136 kHz amateur radio band.
8.467 MHz IF for CC display is available for the Chinese clone counter_CC_8467IF.hex.
You will need an preamplifier to measure the KN-Q7A internals but make sure that you will use one with a high impedance input in place. Try to measure your local oscillator and you will understand.
The high input impedance amplifier is based on common sourced parts, no special JFETs at all and basically it works. it’s based on the work of wb9kzy.
I would love to run a spice simulator to found out the gain…
The DL4YHF frequency counter has been cloned by our Chinese friends, you can find one on ebay/banggood/dx for about 6 Euro, complete with PCB and parts !!! Ordered one.