CTCSS for the Yaesu FT290R Mk1

The FT290R was introduced in 1981 and proved extremely popular as a portable 2 Metre multimode transceiver. It was replaced by the FT290R Mk2 in 1986 (See separate article). The rig originally provided the then-standard 1750Hz tone burst for opening repeaters. The tone generator was built onto the main PCB and was accessed by pressing the ‘Call’ button which momentarily switched the rig into transmit also.

This article describes the installation of an excellent CTCSS module designed and built by Colin Tuckley G8TMV in a fellow club member’s 290. The installation includes audible annunciation of the tone in use in Morse code, which is particularly useful as the rig’s owner is a white-stick operator. The CTCSS tone is selected from the front panel using the repurposed ‘Call’ button, and the board is powered and switched so that the CTCSS tones are generated only in FM mode on transmit and only when repeater shifts+ or – are selected. If CTCSS were needed in simplex mode, eg. for Echolink, the switching would need to be modified.

G8TMV has recently redesigned his board resulting in a smaller footprint (30mm x 35mm) and only 5mm in depth. This is fortunate as the new board is just small enough to squeeze between the control board and the keypad board (with suitable insulation). There is very little spare space in the rig otherwise, unless the battery container space is sacrificed.

The CTCSS board is supplied with 6.8 volts derived from the FM 6.8v terminal on the regulator board. Reference to the circuit diagram reveals that repeater shifts (either +ve or -ve), are selected by grounding one of two lines via S3c. Isolating diodes are therefore connected to each of these lines to ground the input (LED) side of an opto isolator only in repeater mode. The output side of the opto isolator is wired in series with the 6.8 volt supply, resulting in CTCSS operation only in repeater mode. This is very similar to the method already described for the Icom IC290D. The board is activated by grounding the PTT line, which is straightforward, as the 290’s PTT line is grounded on transmit.

Repeater Shift Selection

The tone selection is made by grounding the control line (labelled ‘But’ on the G8TMV board). The Yaesu circuit diagram (below) shows the front panel ‘Call’ button grounding the ‘T Call’ line. It was decided to redesignate this switch as a tone select control as the T Call (toneburst) function is now redundant. Significant angst was caused by the finding that the Call button did not, in fact, connect to ground. Eventually I discovered that the switch consists of two metallic terminals which are ‘shorted’ by a conductive rubber disc resulting in an ‘on’ resistance of around 100 Ohms. Fortunately, this resistance is sufficiently low as to reliably pull the control line ‘low’ enabling tone selection to function as intended. One end of R4003 is lifted from the PCB and the vacated hole is used to connect the’Call’ button to the G8TMV board

T-Call switch connections and FM 6.8V connection

As with the other installations of this board described on this site, the LED annunciator output is used to switch on an NPN transistor which grounds a Piezzo buzzer enabling the annunciator to be audible in Morse code. In this installation the NPN transistor, its base resistor, the buzzer, the opto isolator and its current limiting resistor are assembled ‘dead bug’ style into a small insulated cluster which tucks almost between two circuit boards and allows short wiring between it and the CTCSS board.

Repeater Mode Selection and Audible Annunciator

Connection of the tone board’s output caused some difficulty. The usual practice is to inject the tone after the deviation adjustment control (VR2002). This avoids attenuation of the low frequency CTCSS tones by the microphone amplifier filters and allows independent adjustment of deviation and CTCSS tone level. Unfortunately, the Yaesu documentation available is rather poor. The manual contains some black and white photographs which identify adjustment points, semiconductors and other major components. However, most of the passive components remain unidentified. There are no component designations on either the component or the solder sides of the circuit boards, and the values of various components on the circuit diagram appear to differ from the values given in the component listing. The result is that I found it almost impossible to accurately navigate around the PCB and to know precisely where I was! In the end the best tone insertion point was found by educated trial and error but I must confess that I could not say exactly where on the circuit diagram that point is. The best I can say is that I believe it to be just after the deviation adjustment potentiometer and that the point shown here does work.

The result is a very neat, unobstrusive installation which allows easy selection of CTCSS tones from the front panel with audible identification of the selected tone whenever the rig is switched on and repeater mode is selected. The process of installation is not unduly difficult, requiring only the ability to solder well and deal with through-hole type components. Other than lifting one end of a resistor from the PCB (R4003), no permanent alterations are made to the radio so that it could easily be returned to its original state if required. There must be many FT290Rs which could be brought out of retirement and provide useful service with this conversion.

Bill of Materials

• G8TMV tone board  (http://www.tuckley.org/ctcss/)
• NPN transistor (PN2222, BC547 or similar)
• Piezzo buzzer –must be rated to work below 6.8V e.g. Pro-Signal ABI-009-RC (CPC or Farnell)  Pro Signal ABI-009-RC Buzzer Datasheet
• Resistors 220R and 270R 0.25W or 0.125W
• 2x 1N4148 Diodes
• Opto-coupler (4pin e.g. Sharp PC817 series)  Sharp PC817 Opto-coupler Datasheet
• Thin multi-strand wire in various colours. (1mm diam.)
• Thin (2mm diam.) screened audio cable
• Heat-shrink tubing
• Laminating pouch

G8TMV Board Update

Please note that Colin has since released his Rev. 5 board which is slightly smaller and also includes a ‘down’ button. This would enable the tone to be selected by scrolling up or down the list, but would require an extra switch. The new rev. 5 board can be used exactly as described here by using only the ‘up’ button.

Installation instructions

1.  Unscrew the telescopic aerial. Remove the top and bottom panels by removing 2 crosshead screws at the rear ( top panel) and open the slide lock (bottom panel). It may also be a good idea to unsolder the speaker lead from the speaker. Remove the battery case. Unscrew and remove the two aluminium side strips. Use a 10mm socket to remove the front studs. Remove the 4 crosshead countersunk screws holding the plastic front panel to the chassis sides and ease the front panel forwards slightly.

2.  With the rig upside down and the battery case removed, the regulator board can now be eased away upwards. The regulator board is the one closest to the battery container and carries the lithium back-up battery and a fuse. In the rig shown, there were dried out remnants of tape and adhesive around this area which were cleaned off. Also the back-up battery had expired (exploded) and was replaced during this installation with a coin cell case soldered to the PCB to ease future replacement.

3.  6.8Volt Supply: Locate the connector at the top edge of the board and solder a wire to the land shown below. This is the 6.8 volt FM supply. When the PCB is back in place this wire will pass between the top edge of the PCB and the battery tray.

4.  Tone Select: Unsolder the end of R4003 and lift it from the PCB, as shown below. From the component side of the board insert and solder a wire to the land vacated by R4003. This is the connection to the T-Call button.  I slipped a short length of heatshrink sleeve over R4003 to isolate it.

Connections to Regulator Board

The regulator board can now be replaced in its locating slots.

5.  PTT: With the rig still bottom side up, unsolder the ground strap from the top left corner of the keyboard PCB. This is the board closest to the front panel. Ease the front panel away to expose the wiring at the back of the microphone socket. Solder a wire to the terminal third down on the outer aspect of the socket. The existing wire is white/green in the two examples I have seen.

PTT Pin (Note rig is upside down)

There are two alternatives to soldering to the rear of the microphone socket. The first is to connect a wire to the pin next to the relay (see below) and run the wire forwards and then feed it through to the underside of the radio. The other potential connection point is the center pin of the ‘Standby’ jack on the left hand side of the rig. If there is any doubt, check for direct continuity with the socket pin shown above.

Alternative PTT Main Board Connection

Alternative Standby Jack PTT Connection

6.  Repeater Mode Selection: Turn the radio top side upppermost. Identify the 12 way connector on the top right hand side of the control unit PCB just in front of the screening enclosure. The left hand two connections (pins 11 and 12) are what we are interested in. Ease the board forwards away from the screened enclosure to enable access to the soldered connections on the PCB. Take the two 1N4148 diodes and trim and tin the cathode (bar end) leads at about 6mm. Carefully solder each diode to the lands corresponding to pins 11 and 12 of the connector. The other ends of the diodes (anodes) are soldered together and to another length of connecting wire. This connects to the opto-isolator LED (pin 2) via a 270R resistor. Apply some heatshrink sleeving to cover the diodes and the junction with the wire and dress the assembly so that it sits neatly between the control unit PCB and the screened enclosure. Feed the wire between the control PCB and the keyboard PCB, to the underside of the rig.

Repeater Mode Selection Diodes

7.  Ground: Offer up the front panel and refit the 4 screws connecting it to the chassis sides. Re-solder the ground strap to the keyboard PCB and solder a wire to the same point. This is the ground connection for the tone board.

8.  Tone Output: I used thin audio screened lead (2mm diameter) connected as shown below. Feed the screened lead across the print side of the main PCB and underneath the regulator unit PCB.

Tone Injection Point

9.  The tone encoder board now needs to be insulated. I fabricated a pocket by cutting, scoring and folding an envelope made from a 125 micron laminating pouch which was passed, empty, through a hot laminator. Alternatively, suitable plastic could be rescued from the recycling box. Measure and cut out the shape shown below and lightly score the creases to enable the folds to be made accurately. Punch holes to allow for connecting wires to reach the board, the hole in the top edge allows adjustment of the tone output level trimmer.

Insulating Pouch (Dimensions in mm)

G8TMV Board about to be enveloped

10.  Now build the opto-isolator / buzzer cluster. I started by extending the +ve lead of the buzzer with tinned copper wire. Pins 1 and 4 of the opto-isolator were gently bent so that they could both be attached to this wire, which is then connected to the 6.8V supply wire. Connect buzzer -ve to the transistor collector. Connect the base to the 220R resistor, the other end of which is then wired to the ‘LED’ pad on the tone board. The transistor emitter is wired to ground at the same point as the ground wire to the tone board. Opto-isolator pin 2 connects to the 270R resistor and then to the wire from the two diodes. Opto-isolator pin 3 is wired to the +ve pad on the tone board.

As all these connections are made, slip thin heatshrink sleeving over the joints and shrink it with a hot air gun or hairdryer.

Buzzer Assembly under construction

11. The board can now be wired up; screened lead to ‘Out’ and ‘Gnd’, single wires to ‘+ve’, ‘Gnd’, ‘PTT’, ‘But’ and ‘LED’. Remember to thread the wires through the nearest hole in the insulation envelope before soldering to the appropriate pad.

12.  The insulated G8TMV board will just fit between the keyboard PCB and the control unit PCB, inserted from the underside of the rig, just next to the mode switch. (See below).

G8TMV board in its final resting place

When working properly, put heatshrink sleeving over the buzzer assembly and tuck it between the edges of the control PCB and the keyboard PCB.

Final positions of Tone Board and Buzzer Assembly

Remember to resolder the speaker lead and refit the side, top and bottom case panels.

Testing and Commissioning

1. Switch on the rig.
2. Set MODE to FM,+ or – repeater offset.
3.  There should be an audible Morse code character.
4. Press the ‘CALL’ button. Another Morse character should be heard. With successive presses of the ‘CALL’ button the CTCSS board will scroll through the 10 available tones. When the tone you wish to use is selected press and hold ‘CALL’ until you hear a beep. That tone is now set as the default tone until deliberately changed.
5. Finally, the tone deviation needs to be set by adjustment of the trimpot on the board. Ideally this should be done using a deviation meter to set the tone deviation to 250-300Hz. Alternatively, the pragmatic approach is to slowly advance the injection setting to that which reliably opens repeaters.

References:

Colin Tuckley G8TMV

Sharp PC817 Opto-coupler Datasheet

Pro Signal ABI-009-RC Buzzer Datasheet

G4KQK

November 2016