The basic idea was to make installation as easy as possible. That and the intention to keep the connection between the display and main counter unit as short as possible, resulted in the istallation as shown on the photos below. The double sided Scotch tape is used to attach the main counter bracket to the top of the VFO. The doublesided tape is available in different thicknesses, use the thinnest you can get.

Despite the initial assumptions that the connection between the main and display board could be a source of interference, it turned out that the major source of interference is actually the microcontroller itself or more precisely its proximity to the transceiver's bandpass filter board. The interferences are otherwise quite weak, with the antenna connected they are barely noticeable. Some "birdies" may be spoted in the 15 m and 10 m bands, but as already mentioned, only if the antenna is disconnected and the AF volume potentiometer turned way above normal listening level. As soon as the antenna is connected to the transceiver, the birdies, or at least most of them, dive into the HF background noise, picked by the antenna.

Installation II

Experiments with the replacement frequency counter have shown that the connection between the display and the main board, despite the relatively high multiplexing frequency of 96 kHz and changing nature of the sequence as well as width of the pulses at the display board bus, does not actually cause any internal (local) interference to the transceiver. Considering that and trying to follow the installation concept as originally implemented by the manufacturer, seemed like a better idea. Especially since such an installation results in an increased distance between the counter's microcontroller unit and transceiver's bandpass filter board. The number of unwanted "birdies" has been further reduced and limited mainly to the 10 m frequency band. Again, with a decent antenna connected, the few remaining "birdies" are almost impossible to spot.

Replacement 5V power supply regulator and the TS-820 (base) model installation particularities

The original frequency counter requires precise adjustment of both input signal levels. The replacement frequency counter is less demanding in this regard. However, when installed in the base TS-820 model, it is still necessary to adjust the BFO level as it seems to be set to the minimum level by the manufacturer.

The BFO signal level setup is described in the transceiver's service manual and requires an RF voltmeter with a high-impedance input. In the absence of a suitable measuring instrument, try to ajust the TC1 so that a reliable frequency measurement and a stable frequency display is obtained in both receive and transmit.

There was no factory installed frequency counter in the base model TS-820 (non "S" version) transceiver. Besides the counter module and coresponding display unit the 15 V to 5 V linear power supply voltage regulator is also missing. To solve this issue a simple replacement voltage regulator was designed. The regulator is built on a double-sided 1,5 mm thick PCB. The current consumption of the replacement counter is drastically reduced compared to the original counter, therefore a simple LM7805 IC voltage regulator can easy handle the necessary voltage drop even without an extra heatsink. Heat dissipation to the PCB as well as through a 33 Ohm resistor is sufficient for the regulator to heat up only moderately.

The replacement power supply unit can be installed to the spacers above the power supply choke, as in the case of factory provided solution or it can be placed besides the replacmenet frequency counter and attached by the plastic mounting clamp (see pictures below). The later requires an additional metal mounting bracket cut and bent out of a 1 mm thick aluminium sheet, as suggested in the sketch below.

Please note that the replacement 15 V to 5 V regulator is only designed to power the replacement frequency counter. The replacement voltage regulator cannot power the original Kenwood frequency counter.

Plastic parts 3D printing

3D printing of the plastic parts in the PLA should be good enough in most cases. If operation in a higher temperature environment is expected, a more resistant PETG can be used instead.