Re: Trio TS711 & 811
OK
Thought I would just report back on my experiments to get CTCSS working on a TS711E and a TS811E
Fig 1 attachment below is taken from the Trio Service Manual. The PCB layout is correct but the circuit diagram is not. C2 and C3 should be on the 5v rail not the tone enable line.
I played around with using a 1 MHz ceramic resonator instead of a crystal. While it oscillates fine I could not get the frequency accuracy good enough to give a consistent on frequency tone every time. Finding 1 Mhz crystals was a bit of an adventure but I did manage to obtain a couple and they oscillate bang on frequency.
The output of the chip through R1, R2 and VR1 I can't get to work. I know the values are correct because I have a high resolution picture of an original Trio CTCSS board as fitted in a TS711A. The only way it works for me is to jumper from the non chip side of R2 straight to the tone output pin TI.
For anyone who has found the mod elsewhere on the Internet, cutting the track and linking it on the back of the tone button will activate the CTCSS menu on the display. The rest of the mods involving removing diodes as far as I can see will just mess your radio up and expand the frequency range and alter the step rate on the VFO. I also changed the value of R4 accross the crystal from Trio's 2.2 M ohm to what the chip maker suggests which is 1 M ohm.
I have this fitted in my TS811E as shown in fig2 and it works perfectly and it cost me less than £10 to do.
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