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[aprssig] Does anyone have a fix for the intermittant tone encoderon the TH-d7ag 70cm side?

Thomas t hamaddict2001 at yahoo.com
Thu Mar 22 17:16:52 UTC 2007


Hi Dave and thanks for checking this out....
   
  You need to run the th-d7 into its stock antenna or another rubber duck and run it at 5w to see the problem most prominently.  For some reason, as I said before, when the rig is connected to a dummy load the problem is much less evident.  Also, on low power the problem is less evident.  Together, with low power into a dummy load I would imagine you might not see the problem much at all.  Could you please try with the d7 at 5w on 70cm into a rubber duck antenna?
   
  All local users of the th-d7ag (we had 4 including myself), had the same problem with the clubs repeater, and no other users did.  I also tested at least 2 of those other rigs against my ft-817 and found they had the same issue as my d7ag.   
   
  I tested other model hts with my ft-817 and could not duplicate the problem with them.  Also, the ft-817 has no tone problem with the repeater.
   
  I tested all of the exhibit radios at Kenwood's Dayton booth, and I even tested the personal d7ag rig a salesman in the booth had and all exhibited the problem...but this was a few years ago.  
   
  I think there is a lot of merit to the audio tone mixing idea.......
   
  Thanks again,
  Tom-N2YTF

Dave Baxter <dave at emv.co.uk> wrote:
  Hi...

The more and more I think about this, from the original description below, initialy I'd suspect the FT-817's and the repeater's RX tone DECODER's ability to work correctly, in the presence of other very strong LF frequencies in the transmitted audio path. Al's (K9SI) comments imply thinking on the same lines. But posibly a different root cause reasion. (poor LF) removal of the mic audio in the D7, before mixing with the ctcss tone, so any "spurious" LF will totally swamp the ctcss (that is only at a small deviation level compared to the mic anyway) so momentarily causing the reciving tone detector to "loose" lock.

Have you consulted with your local repeater keeper? Do any other local users have the same problem? Do "ALL" of them use D7's? Etc, etc...


Looking at the schematic in the manual, there seems to be little LF rejection of the mic signal, unless U509 (pre-emphasis and limiting) handles that too. Both the TNC tones and ctcss tone is applied after that chip. From there, it goes to the RF side, and the VCO's.

About the only places you could alter things as far as I can see, would be C559 and C557. But, there are other parts in that area tied in to the mic audio path and U509. Without detailed data as to how U509 does what it does, take great care... Messing with the signal path downstreem of that lot, could grosly affect (in a bad way) how many other aspects of the D7 behaves.

Have you tried you test, with a false mic connected? To make sure it's not accousitc LF that is indeed causing the problem. The VCO on the UHF side could be a bit microphonic, in that case there is I suspect next to nothing that could be done.


As I have the time (unusually) at the moment (I'm at home recovering from Flu) I went and found my D7, and an old Standard C510A (minature dual band FM radio, but with all the tone and ctcss etc bell's and whistles. Nice bit of kit.) to duplicate your experience.

Sadly, I can find nothing wrong with the D7's tone encoding (or decoding) on UHF (or VHF) and this is a TH-D7e, but with the frequency expansion mods done. (D7A's and AG's are US spec models. European spec will be the e versions by the way.)

Anyway...
No matter what I do, "clapping" the front pannel, tapping it with my fingers, with or without a dummy plug in the MIC jack, the "Other RX's" tone decoder and squelch stays open when the D7 is transmitting, just as it should...

The D7 is working at EL power into a dummy load, the C510 also has a dummy load, neither radios make the other full scale in this situation, except when placed right next to each other.

This D7 was made in Japan, in 2001 for the French market, and is a V2.0 model. It's also running on the 4 AA drycell pack, as if that would make any difference.


I still think, what you are seeing, if you say you've seen exactly the same on many radios, could be the behaviour of your "Test Gear", ie, the 817 in the presence of less than optimal input. 817's have their "Features" too I hear. (I don't own one)

One thing that is known about the D7's and UHF working, is that the RF carrier frequency can be "off" by up to a couple of k at times. Seems to be thermally dependant too. Some are worse than others, but as most people don't use them for anything other than voice comms at UHF, they tend not to notice...

If either your D7 or 817 is significantly off frequency, that could also have an effect on this problem.

Take care, tracking down this sort of thing takes a lot of time and planning. Remembering the ABC's of any investigation. Assume nothing, Believe nothing, Check everything. That last bit is the killer...

I've done what I can, with what I have, and I cannot confirm the problem with my TH-D7e at least...


Best 73 etc...

Dave G0WBX.



________________________________

From: Thomas t [mailto:hamaddict2001 at yahoo.com]
Sent: Sun 18/03/2007 03:46
To: aprssig at lists.tapr.org
Subject: [aprssig] Does anyone have a fix for the intermittant tone encoderon the TH-d7ag 70cm side?


Does anyone have a fix for the 70cm tone encoder problem on the TH-D7ag? 

Every rig I have tested has had the problem, but I don't think I have tested any rigs manufactured in 2006 or latter. The problem was also reported on European d7ags.

This problem prevents me from using the d7ag as a rig because my club's repeater is on 440 and uses TSQ.....the tone encoder problem makes me drop out too much. 

Kenwood is aware of the design defect, but has no fix. My ht died on the operating table at home during my own work after Kenwood's 3 attempts at fixing the problem with some experiments amounted to naught. I was frustrated with Kenwood, but I guess they did try. I would buy the rig again if current production doesn't have the problem, although last year I tested one at a local shop and it too had the problem.

In case you aren't familiar with the tone encoder problem on 70cm, you can experience it by following this procedure:

1. Set a second radio (I used a Yaesu FT-817) to 446.000mhz WITHOUT TONE SQUELCH SET.

2. Set the TH-D7A(G) to transmit on 446.000mhz with tone encoder set to a tone of 136.5.

3. While holding down the PTT on the TH-D7A(G), lightly tap your palm against the face of the radio as if you were clapping your hands repeatedly (or tap your fingers hard repeatedly on the face of the TH-D7A(G)), LISTEN TO THE SECOND RADIO AND HEAR YOUR FINGERS TAP THE TH-D7A(G)- NO PROBLEM. Now go to step 4.

4. Set the second radio (I used a Yaesu FT-817) to 446.000mhz WITH TONE SQUELCH SET TO 136.5.

5. While holding down the PTT on the TH-D7A(G), lightly tap your palm against the face of the radio as if you were clapping your hands repeatedly (or tap your fingers hard repeatedly on the face of the TH-D7A(G)), LISTEN TO THE SECOND RADIO AND YOU WILL NOT HEAR YOUR FINGERS TAP THE TH-D7A(G) REPEATEDLY BECAUSE THE SECOND RADIO'S SQUELCH WILL BE CLOSED OR WILL CLOSE INTERMITTENTLY.

Thanks for your input,
Tom- N2YTF


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