97.4PL not supported by Kenwood TS-811/TS-711?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by AD8BU, Oct 10, 2019.

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  1. AD8BU

    AD8BU Ham Member QRZ Page

    Good evening everyone. I have a feeling I already know the answer to this, but I want to ask anyway to confirm my suspicions...

    I just got a TS-811a and it has the tone board in it, but I can't select the 97.4 PL tone that I need for one of my local 70CM repeaters... I checked my TS-711a and it too skips over 97.4. Both go from 94.8 to 100.0. Is that tone just not supported on these radios? Any chance there's a workaround?

    Thanks in advance.
  2. K7JEM

    K7JEM Ham Member QRZ Page

    Right. Some early radios used a slightly different list of tones, with 32 and 38 tones being somewhat standard back in earlier times. The Kenwoods had a list of 37 tones, IIRC, but did not include 97.4. The only workaround I could think of would be to install another tone board fixed on 97.4, that could be toggled on or off with some sort of switching arrangement. You could select "off" on the internal encoder, then flip a switch to activate the added unit.

    You could probably design a small Arduino or similar that would look at the programmed code, and deselect the internal encoder, and activate the add on encoder when a certain tone that you would never use was selected. But as far as I know, the TU5 doesn't have capability to encode the 97.4.
  3. K7JEM

    K7JEM Ham Member QRZ Page

    OK, some good news. I downloaded the service manual for the radio, and it has the schematic of the tone encoder in it. The tone encoder is an MX315 IC, which does in fact have the capability to generate 97.4, but apparently it is just not in the programming list that Kenwood placed into that radio. It should be possible to tell the unit to program that frequency by adding a simple switch.

    Here is how to do it:

    The program for 118.8 is 011010 and the program for 97.4 is 111010, which is only one bit different. The bits have parallel entry, and that first bit is tied to pin 6 of the MX315. If the pin is left "open", an on-chip pull up resistor will pull it to "one", so if you cut the trace going to pin 6, then program 118.8 into the radio, that first bit will be a 1 instead of a 0 at the chip, meaning it will now encode 97.4. If you only need that tone, that is all you have to do. If you want all the other tones, you would need to install some sort of external switch to either complete the trace as normal, or open the trace which will force that first bit to always be 1.

    So, to encode 94.4, you would program 118.8, then open that trace. The chip will then see 111010 and encode 97.4. Easy to do mod that can be easily reversed to make the radio "stock" again at any time.
    NQ1B, AG5DB and KK4CUL like this.
  4. K7JEM

    K7JEM Ham Member QRZ Page

    OK, forget that last post. The data sheet I was looking at was for the MX315A not the MX315. Apparently, the MX315 was an earlier model which did not support the tones 69.3, 97.4, and 206.5. So, the chip in there will not work on that tone.

    However, it looks like you could find and substitute in the MX315A and make it work, if you really wanted to. I will look to see if I can find the difference between the MX315 and 315A programming to see what would change in that regard.
  5. KD8TUT

    KD8TUT Ham Member QRZ Page


    You could go with a Piexx PIEXX TU-5 after market tone board. I'm pretty sure it's capable of those tones.

    Also, I've got a tone board in my 711a. If you want me to pull it for testing you are welcome to take it for a bit and test it.

    W8NDB likes this.
  6. K7JEM

    K7JEM Ham Member QRZ Page

    The data sheet on that indicates that it is an exact functional replacement, so unless the actual chip being used for encoding was known, it probably won't do it either.
  7. KD8TUT

    KD8TUT Ham Member QRZ Page

    I'm sure a short phone call or e-mail can resolve whether it's the MX315A or not. If I remember correctly my board is aftermarket from 2015.
  8. AD8BU

    AD8BU Ham Member QRZ Page

    Well, I already sent an email over to you Michael... before I realized you had replied to this post. LOL *facepalm*

    Thanks for the info K7JEM! Knowing what I know now about the early MX315A vs the later production MX315A it looks very promising that I may be able to add a switch to enable that frequency. I wonder when the production switchover date was?

    Data sheet here: http://pdf.datasheetcatalog.com/datasheets2/17/179186_1.pdf

    That being said, I can't seem to find a source for the MX315A chips. They appear to be long out of production. The Piexx board pictures I see online all have the chip markings filed off, but I can see its a 20-pin surface mount chip which means its probably not an MX315A series IC. It may be a FX365DW chip, or a variant of the MX365.

    Michael, I think its time we did some reverse engineering :)
    If I'm lucky, I may be able to use my original TU-5 board with the MX315A chip, otherwise I will barrow your Piexx board to see if we can reverse engineer it and find out what chip it actually has on it and go from there.
  9. K7JEM

    K7JEM Ham Member QRZ Page

    The chip used in the Kenwood is supposedly the MX315, original version. The MX315A is the newer alternative which is functionally identical in programming, except it has the added 3 tones mentioned above. You can remove the board and verify if it is a 315 or 315A, but I think you'll find that it is the original 315.

    I will look some more and see if there is any source for a 315A, I haven't been able to locate one yet. But that would be the easy solution, change the chip and install a remote switch to get the additional tone.
  10. AD8BU

    AD8BU Ham Member QRZ Page

    After I posted that I almost immediately found the original data sheet. It didn't help that there is a typo in the datasheet for the MX315A variant that calls the original an MX315A as well. *facepalm* again...

    I did an image search and it shows that the original board uses an MX315J ceramic package IC. I then found a listing for MX315AP on AliExpress and on Ebay, but the eBay seller wants over $35 USD per chip! Its also a seller that has been known to sell counterfeit chips in the past. I will check to see what chip is on my board and I may look into ordering the ones from Ali Express.

    I would prefer to mod the original board as opposed to the Piexx one as I am much more comfortable working with thru-hole components than surface mount...

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