Add a digital display to your Kenwood TS-520S Transceiver

​The Problem

As any owner of a Kenwood TS-520S can attest to, it is a real pain to calibrate the analog tuning dial so that the frequency read is the truly accurate. The process involves changing the function switch to CAL-25kHz, this is an internal reference signal, then you turn the main tuning knob until you zero beat the the internal reference signal, adjust the dial scale until it shows the correct reading. In order to maintain turning dial accuracy, you have to do the dial calibration again when changing bands or modes of operation (Upper Sideband, Continuous Wave, Lower Sideband). I thought it would be cool to eliminate all of this calibration nonsense by adding a digital frequency counter to the to the TS-520S so that you always have the tuning frequency accurately displayed.

​Video showing the process of zero beating for dial calibration against station WWV

​Easier procedure for analog dial calibration by K4TFJ

The DG-5

Kenwood did build an add-on digital display for the TS-520S called the "DG-5 Digital Display". Kenwood claims that it had an accuracy to 100 Hz. It required multiple RF connections to the back of the TS-520S. The TS-520S also provided 13.8 Volts DC power to the DG-5 unit was well. These units are difficult to find, and when you do find one, they are expensive as most ham radio enthusiasts know that they are rare. "Rare" and "expensive" are not in my vocabulary, so I decided to built my own frequency counter. Image Credit

​The Bad News

One of my goals was to provide a readout of the current tuning frequency on the frequency counter but it does not look it is quite that simple. I am not sure what "Magic" the DG-5 does to directly perform a readout of the tuning frequency. It somehow does this while monitoring the signals of the CAR OUT, HET OUT, and VFO OUT jacks on the back of the TS-520S.Here are the outputs and their frequencies:VFO OUT: Same frequency variation not matter what the setting of the Band Switch.With both the Main Tuning Knob and Sub-dial set to 0: 5.5MHZWith the Sub-dial set to 600 and the main tuning dial set to 0: 4.9Mhz CAR OUT: Constant 3.2987Mhz no matter where the tuning dial or Band Switch are set.HET OUT: Changes with the Band Switch setting:1.8 - 10.693MHZ3.5 - 3.1239Mhz7 - 15.893MHZ14 - 22.892MHZ21 - 028 - 028.5 - 0I have not yet solved this riddle.

The Good News

If you connect your frequency counter to the VFO OUT on the TS-520S, with some simple math you should be able to determine the true tuning frequency.For you consideration:With both the Main Tuning Knob and Sub-dial set to 0: 5.5MHZWith the Sub-dial set to 600 and the main tuning dial set to 0: 4.9Mhz 5.5MHz - 4.9MHz = 600kHzFormula:True Tuning Frequency = Band Switch + + 100kHzFor example, if the Band Switch is set to 7 and frequency counter reading is 5.200MHz, the true dial frequency is:7MHz + 200kHz + 100kHz = 7.300Mhz

​Connecting your Frequency Counter to the TS-520S VFO Output

I use a short video cable with RCA jacks on the ends to connect my frequency counter to the VFO Output on the back of the TS-520S. I removed the RCA jack from one of the cable ends, stripped the insulation back and separate the outside braid from the internal conductor. I then tinned the ends of the outside braid and internal conductor so that they would not come unwound and connected them to the Fahnestock clips which serves and input terminals to my frequency counter. See area circled in the above picture.

The Frequency Counter in Action!

Conclusion

Adding a PIC based frequency counter is a great way to calibrate your tuning dial and provide digital accuracy to your vintage Kenwood TS-520S SSB Transceiver.