This article describes my installation of Colin Tuckley G8TMV’s CTCSS module in the Yaesu FT221R. The rig was acquired at a bargain price from the National Hamfest and had been sitting untouched in the jobs queue. A request as to how to install the board in the radio prompted this project.
The board is now in version 5, measuring 31mm by 28mm. This most recent version adds a new ‘down’ connection, allowing the use of two switches to scroll both up and down the list of available tones. In this installation I am still only using the ‘up’ button due to the challenge of accommodating additional switches.
If the board is powered while the transceiver is in receive mode it is easy to select the CTCSS frequency required, in this case (as in my other installations) by an audible tone giving the selection in Morse code. In this installation, the CTCSS tone is only generated when the transceiver is transmitting on FM, in Repeat mode. If users wish to use CTCSS in simplex mode then there will need to be changes to the circuit.
Here is the circuit I designed for the installation. It is similar to the arrangement used in my other descriptions, IC290D, FT290R Mk1 and Mk2. My article re the IC290D might well be useful in conjunction with this one.
As the tone board is only to be used in FM mode, I had anticipated stealing a supply for it from the mode switch when switched to FM. Unfortunately, in the FT221 there is no single FM supply rail which is powered in both transmit and receive. S3B switches 8 volts to pin 14 on the AF amp board and pin 6 on the FM IF board ‘FM8V’, but only on receive. Studying the circuit diagram, I found that S3E directs 8 volts to pin 9 of the Mic Amp board ‘TX8V’ in transmit mode and only on FM. The solution was to connect both of these supplies via diodes (“diode OR-ing”) so that either would supply the CTCSS encoder. A 10uF capacitor is connected from the diode junction to ground in order to prevent the encoder board restarting if its supply voltage drops during Tx/Rx switching.
In repeat mode, the Rep/Rev switch supplies 13 volts to a front panel LED indicator (D11) via R14. This same 13 Volt supply is tapped into to supply the LED side of an optocoupler, which is then used to enable the supply to the encoder.
As in previous installations, the encoder’s LED output is used to switch on an NPN transistor which enables a piezo sounder supplied from the 13 Volt line.
As is usual, the FT221’s PTT line is connected to ground to switch to transmit. The encoder’s PTT connection is simply made to the PTT terminal on the Mic connector.
The tone encoder’s audio output is connected to the Mic Amp, via the slider of the deviation adjustment trimmer VR1101. Conveniently, Yaesu have brought this connection to one of the board edge connectors, so access is easy. Unfortunately, I found in practice, I suspect due to the low value of VR1101 (2K), that connection of the encoder’s output to VR1101 caused the output to be drastically attenuated. Insertion of a 22K resistor in series with the audio connection improved matters dramatically.
The remaining issue is how to arrange switching to change the tone selected. There are no redundant front panel switches which could be re-purposed. One option would be to drill the rear panel in order to mount a momentary push switch or a centre biased SPDT miniature toggle switch for up and down selection. Not wishing to alter the outside of an otherwise original radio, my solution utilises an unused contact on the rear mounted DIN socket. A miniature momentary push switch mounted within a DIN plug allows the tone to be changed with no physical alteration to the appearance of the rig. My example is a late model with the internal wiring arranged for the use of a YC-221 digital display, leaving two contacts unallocated on the DIN socket. Earlier versions may not have any unused terminals so drilling and mounting a new switch may prove the best option here.
Bill of Materials
- Tone encoder from Colin Tuckley
- Opto-isolator eg. PC817
- NPN transistor eg. 2n2222 Almost any small signal NPN will do
- Piezo buzzer eg. ABI-001-RC (CPC)
- 2 diodes. (I used 1N4148)
- 10uf 25V Electrolytic capacitor
- 1K resistor x3
- 22K resistor x1
- Momentary push switch eg. CPC SW05489
- DIN plug 5 pin 180′ Metal bodied eg. CPC CN00052
- Hook-up wire
- Thin screened lead for tone output
There is enough room within the FT221R to mount the encoder board and associated components properly. I therefore designed and made a small single sided PCB on which to mount everything. This board was then fixed with 2x M3 bolts to the bulkhead behind the front panel on the right hand side. There are alternative suitable places. As the circuit is simple, veroboard or plain perforated board could also be used.
The encoder board was mounted on the PCB using component leg offcuts as short legs, leaving around 3-4mm between the boards.
Instructions for installation
- Remove top of case: 4 pull-studs. Remove bottom of case by removing 12 x M3 screws. Disconnect the loudspeaker.
- Remove the tuning knobs. Each is attached with 2 grub-screws. Use a straight blade driver.
- Remove 8 x M3 screws holding the front of the radio to the chassis – 2 on each side and 2 top and bottom near the panel middle. The front panel can then be carefully eased forwards and tilted down over the tuning shaft.
- Mount the PCB in your favoured position. The only problem with the position I chose is the difficulty of adjusting the encoder output level – a short trimming tool is needed when the front panel is in place.
- Solder wires to the PCB. I used 1mm vero-pins but wires could be directly attached to the board. (See below)
- Route the 13V supply wire to behind the ‘Rep’ switch and solder to the point shown below, circled in red.
- The front panel can now be replaced and fixed. This is an opportunity to clean the inside of the tuning window.
- Feed all the wiring to the lower part of the chassis and turn the set upside down. Solder the PTT connection to the rear of the microphone socket. I actually soldered to the non-grounded lead of C22. (Below)
- The ‘FM8V’ connection is made to pin 6 on the FM IF board connector. (Below)
- The ‘TX8V’ connection is made to pin 9 of the Mic Amp board connector. (Below)
- The tone output is connected to the mic amp board connector (Below). The signal connects to a previously unconnected terminal, marked ’10’. The screen is trimmed back and covered with heatshrink insulation. Also within the heatshrink is the series 22k resistor.
- The ‘Up’ button connection is routed to the rear of the rig and in my example is connected to a vacant pin on the DIN socket (Pin 3). The small momentary push switch is mounted to the metal case of the DIN plug from which the strain relief sleeve has been removed. The switch is wired across pins 2 (ground) and 3.
In practice, the tone select switch protrudes from the rear less than the mains power cable, or the PL259 aerial plug, so it is not obtrusive. Remember also that the DIN plug/switch only need be inserted when it is required to change the CTCSS tone.
- Finally the deviation of the transmitter should be checked and if need be, reduced to +/-2.5KHz. The preset on the G8TMV board should then be adjusted to around +/-250 Hz deviation, or in the absence of a deviation meter, to the minimum level which opens repeaters reliably.
- Once everything is working properly, replace the casework, not forgetting to reconnect the loudspeaker.
- As an alternative to the single switch in the DIN plug, some may wish to drill the rear panel in order to mount the switch. In this case a miniature switch such as CPC SW04080 would enable use of the ‘down’ function as well as ‘up’.
- In these days of 12.5KHz channel spacing, the original FM ceramic IF filter is strictly too wide. Replacing the original with a 455G filter will narrow the IF passband, reducing the risk of adjacent channel interference. This is on my ‘To Do’ list.
- Having installed CTCSS, there is no need now for the obsolete toneburst function. I disabled toneburst by lifting one end of R1013, disconnecting it from pin 14 on the toneburst board connector.
- If it was desired to use CTCSS in simplex mode, the optocoupler could be omitted and pins 3 and 4 bridged. This would mean that the encoder was active whenever FM mode was selected, irrespective of the ‘Rep’ switch position.