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  #1  
Old 08-03-2017, 11:03 AM
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Kamakiri Kamakiri is offline
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Wiring in a CTCSS or PL tone board into an older radio

Here's my latest project, and I could use some advice as to how to proceed.

Recently bought this little number off ebay:

http://www.ebay.com/itm/CTCSS-encode...item2a89493dd2

These are the somewhat lousy instructions that came as a link:

http://isp51.blogspot.tw/2016/02/pro...led-ctcss.html

The radio I'm hooking this up to is a Clegg FM-28 2 meter radio. I have the manual that I can email if anyone needs it to help me answer this question.....

Generally, how do these CTCSS boards hook up? The PTT goes to the mic keying....that I get, but where do the tone wires go? As much searching as I did, everything seems to be a vague reference......

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Old 08-03-2017, 08:45 PM
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I read somewhere that you can inject the tone on the center leg of the deviation adjustment pot, maybe through a resistor to match the impedance. If you can't find any info on it, I have a friend whose a radio tech with the state who might be able to help. I can ask him about it.
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Old 08-04-2017, 09:13 AM
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Yep, I read the same. But where *is* the center deviation pot? Is it on the TX driver board, or somewhere else? And then is it just chassis ground?

This is the only literature I can find on this radio:

http://www.afu-df3iq.de/Hersteller/C...M28_manual.pdf
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Old 08-04-2017, 01:57 PM
tom.j.fla tom.j.fla is offline
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"K"man, If the output is audio then feed it to the "ACC" input of the accessory plug pin # 5. May have to set the level though. Been a long time since I used one of "them there" rigs (:-) Tom.J
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Old 08-04-2017, 03:29 PM
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Page 5, Tone Input, on the ACC jack? Pin 1 is capacitively coupled to pin 5 of the same jack, labeled "tone burst" and looks like it goes on to feed the VCO board.
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Old 08-07-2017, 11:55 PM
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I'm watching this with interest. That clegg and my midland look to be the same set with different badging....If you get this to work I should be able to copy it on the midland.
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Old 08-08-2017, 11:28 AM
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Yep, I believe Midland branded the exact same radio. I found the center deviation pot and wired everything up. The one thing it doesn't tell you is where to put the grounds. The ground for the 12V is obvious. The PTT ground I figured was the other side of the PTT switch, and the third ground was for the tone (the one that went to the deviation pot). I assumed this went to chassis ground.

Well, on this radio chassis ground is the same as the 12V ground. I powered it up with the board hooked up and it was stuck in transmit mode. Didn't chunk the PL tone required repeater either. Also lost audio. I unhooked the PTT ground and it was still locked in transmit mode.

Removed everything, and found that the tone wire to the deviation pot had split the insulation when I fastened the board back down, so I'll give it another go once I get the mic for my Yaesu FT-2400. Since I'm net control for an ARRL traffic net on Tuesday nights, I can't afford to be without a radio if I do something wrong with this one.

Wanted to use my Heathkit HW-2036A that I got working well, but all the picky hams out there keep telling me that I sound off frequency. I'm not off at all, this radio just has a light 833 MHz tone that leaks into the audio from the VCO. From what I've read they're pretty much all like that.
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Old 08-08-2017, 11:31 AM
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Quote:
Originally Posted by Findm-Keepm View Post
Page 5, Tone Input, on the ACC jack? Pin 1 is capacitively coupled to pin 5 of the same jack, labeled "tone burst" and looks like it goes on to feed the VCO board.
I thought of exactly that and would have tried that approach, were it not for this.....
Attached Images
File Type: jpg clegg_fm28_acc.JPG (68.2 KB, 19 views)
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Old 08-12-2017, 11:20 AM
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So the thing about CTCSS is it's basically just an audio tone; and all you have to do is insert it in to the transmission somehow. The trick is you have to insert it *after* any filtering but before modulation.

My guess would be on the VCO board after Q357. The block diagram shows the microphone as entering the VCO board, running through a filter, then in to a modulator. The center leg of RT351 before it goes through C365 should be where you'd want to inject the CTCSS.

As far as the tone input on the accessory plug...typically this is for hooking up a TNC. I mean..I guess you could try inserting tone on to Pin 1, it feeds the VCO board the same place as the microphone..so as long as the mic filtering on that board doesn't filter below 300hz it's fine. They label the line as tone-burst...I have no clue why it's tied to pin 5 through a cap...there may have been a plan for that at one point. That will probably work. Won't hurt to try.
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Last edited by dewdude; 08-12-2017 at 11:27 AM.
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  #10  
Old 08-15-2017, 11:09 AM
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Kamakiri Kamakiri is offline
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That's exactly how I had it wired, center leg of RT351. It turned out to be correct, but when I wired it the first time the insulation rubbed off the wire when I reinstalled that part of the chassis and it had grounded out.

It's working!!!!

These pics show the testing and the final product. For power I just wired it right to the on/off. Not sure whether I should add a tiny toggle or not yet. It's not the prettiest mounting, but there's really not a lot of choice here except installing a ribbon cable and connector and making some sort of artsy box for it. But I'm a mechanic, not a woodworker

Things that the instructions don't tell you:

1. For the grounds, you just tie them all together and ground them to the chassis.

2. Compare the positions of the molded dots on the part to the picture in the instructions and make sure you have it correct. The resistor blocks just below and to the right of the LED display have no polarity.

3. Only the wires shown in the photo are needed. The 4 pin connector by the IC isn't used.

You end up with 4 wires coming from inside the radio.....ground, PTT, Tone, and +12V. That's it!! This is an outstanding kit to order because there's no jumpers or guessing your PL frequency or any of that garbage.
Attached Images
File Type: jpg 100_1914.jpg (84.1 KB, 9 views)
File Type: jpg clegg ctcss board.jpg (105.1 KB, 9 views)
File Type: jpg clegg tone board.jpg (80.7 KB, 9 views)
File Type: jpg fm28 ctcss.jpg (71.0 KB, 9 views)
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  #11  
Old 08-20-2017, 05:13 PM
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I had/have an old Kenwood TR-7850 (or similar) 2m monobander that came out in an era where CTCSS was rarely used...so it was an add-on option. I had a mixed bag of instructions including the Norcom sheet, the ComSpec instructions, as well as the schematic for the radio which showed a circuit for the PL board. I wound up getting more from a description of the wires on the board and reverse engineering with the schematic...I also had a plug available to solder some pins on. I wound up tying it's enable line to the tone-enable from the rig; though since it used a matrix-diode to set up to three tones...I didn't bother trying to take the dip switches off and hack that together. For a while I wanted to get one of the slightly later Kenwood rigs since they did PL tone selection via serial programming...and the chip they used on the Norcomm board has support for that built in.

I bought a good HT and 50 watt VHF/UHF linear and use that if I ever want to VHF in the shack.
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