Retrofitting PL/CTCSS into old radios...

[eccerr0r]

I was trying to see how to get CTCSS retrofit into an old 2m radio I got...

I found a port on the radio that supposedly is used for tone input, so that seems like the best place to inject the tone. The radio supposedly has an internal 1750Hz tone generator but I didn't use that (maybe I should simply change that oscillator's frequency, but will it be accurate enough?). The CTCSS tone seems to be an add on option.

So I tried my simple DDS signal generator with the radio. The DDS generates a 2.5V offset 2.5V amplitude sine wave, hopefully that won't cause an issue...

The repeater didn't repeat I probably should stick in a DC blocking capacitor. However I noticed the repeater seemed to trigger when I unkeyed the radio. Oops: *Kerchunk*

So I tried transmitting to a scanner... I heard the tone and my voice in the scanner just fine!

Strange, will need to do some more research and experiments...

[stj]

Re: Retrofitting PL/CTCSS into old radios...

there used to be generator pcb's on ebay, not sure about detectors though.
or how you program them.
probably best to roll your own with an mcu, and a display.

[eccerr0r]

Re: Retrofitting PL/CTCSS into old radios...

I guess I don't care about detection at this point, but yeah, that's sort of what I'm doing. I have a homemade audio frequency DDS board using a microcontroller with an R-2R DAC. I use a serial port to program frequency into its EEPROM, and then use it on the radio. (The eeprom is kind of flaky as I don't have brownout protection on the MCU so it self erases once in a while, but it's okay, it transmitted the "default" frequency when it loses its programming just fine, too!)

I guess it's possible I need to adjust the amplitude though unsure what it needs to be to get it to work. As this is a really crappy DDS I can't adjust the amplitude through software, I'll have to hack up external circuits to adjust it.

[stj]

Re: Retrofitting PL/CTCSS into old radios...

it would be interesting to scope a modern radio to see the level of tone as a percentage of signal.

[eccerr0r]

Re: Retrofitting PL/CTCSS into old radios...

And that I might have to do, and luckily I have full schematics to one of the radios I have that has a CTCSS board...

[eccerr0r]

Re: Retrofitting PL/CTCSS into old radios...

YES!!! I think I got it finally after a few iterations... I think. My 2m HT now can be used on a repeater!

The first time I was able to hit the repeater with an experiment, I was ecstatic! Had a hard time hearing on my scanner but someone said they heard me. As an experiment I disconnected the CTCSS tone audio AND IT STILL TRIPPED THE REPEATER! I was completely baffled as to what was going on until I heard someone say that my audio quality was pure awful and with that report, was able to deduce what was going on. It turned out it was drawing so much power that it messed up transmitting... and that was triggering the repeater even without the tone fed into the audio!

Now this new iteration, at least the tone generator must be hooked into the stream in order for it to work, so that's a good thing I still need someone to report if it sounds any better or worse... I'm still signal cheating too, though I added a control for deviation, it's a pretty awful signal I'm using: hint: odd harmonics galore!

Hopefully can get someone to comment on it eventually...

So check off: I finally have a 2m radio that can transmit to a repeater! I still need to figure out how to get my PLL to work so I can get that other 2m radio with its 15W transmitter to transmit on arbitrary frequencies, and likewise it needs the same CTCSS hack to hit a repeater.

[eccerr0r]

Re: Retrofitting PL/CTCSS into old radios...

Oh stooge, I *knew* something was fishy with a circuit in the radio. Yup, it looks like Kenwood did build in a simple tone generator after all, much like what I had built externally - after seeing a YT video of someone using it, I figured out how to use it, and it seems to work too. It likewise uses a multiturn (?) pot to adjust tone frequency. I just had to flip the switch the other way to use it.

Oh well, I can still use my hodgepodge on my other radio once the PLL is working Or rather, I should add this functionality into the microcontroller...