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Old 20th May 2020, 8:57 pm   #1
John-39
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Default Kenwood TM322. (Actually a TM-733).

This 2m/70cm radio is rugged and works fine, but its +/-5 kHz deviation is rejected by the local Repeater. Does anyone know if it is easy to reduce the deviation to +/-2.5 kHz?
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Old 21st May 2020, 3:23 pm   #2
Sparky67
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Default Re: Kenwood TM322

Hi John,


I had a quick search via Google to see if I could help, but it didn't throw up any references to a Kenwood TM322 or TM-322. Does it have another designation?


Martin
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Old 21st May 2020, 3:40 pm   #3
SiriusHardware
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Default Re: Kenwood TM322

Couldn't find it either. Is it an amateur specific set or PMR reprogrammed as amateur?
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Old 21st May 2020, 4:14 pm   #4
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Default Re: Kenwood TM322

Silly question, not many PMR sets are dual band...
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Old 21st May 2020, 4:21 pm   #5
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Default Re: Kenwood TM322

It is menu driven? There is sometimes FM and FMN to select.

You need full 5kHz on 70cm and 2.5kHz only on 2m. Hopefully it can cope with the difference between bands.

Any chance of a picture of the front panel and of the part# serial# plate?
It would be something to go on for searching.
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Old 21st May 2020, 9:20 pm   #6
John-39
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Default Re: Kenwood TM322

This is embarrassing! The correct model number of the radio is Kenwood TM-733. I don't know what came over me! Thank you all for looking into it.
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Old 21st May 2020, 9:38 pm   #7
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Default Re: Kenwood TM322

Service manual

http://www.radiomanual.info/schemi/K...33A_E_serv.pdf

See page 63, separate DEV pots for VHF and UHF

Fred
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Old 21st May 2020, 9:47 pm   #8
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Default Re: Kenwood TM322

dodgy-dxer beat me to it, but the VHF deviation preset would appear to be VR2 on the VHF RF PCB, as per this section cropped from the circuit diagram.
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Old 21st May 2020, 9:56 pm   #9
John-39
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Default Re: Kenwood TM322

Thank you Fred for this info. I hadn't managed to find the service manual and I didn't expect the deviation to be adjustable, let alone with separate pots. I was thinking of bin-ing the radio, so many thanks!
John G4IMS
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Old 22nd May 2020, 9:09 am   #10
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Default Re: Kenwood TM322

Thank you SiriusHardware for the the circuit diagram. There are some good YouTube files on measuring deviation, so it looks like an interesting little project to bring the radio back into use.
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Old 22nd May 2020, 11:10 am   #11
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Default Re: Kenwood TM322. (Actually a TM-733).

It's not really good 'form' to do this, but if you can catch the repeater at a quiet moment just have someone open it for you and then adjust the deviation downwards until they tell you your audio through the repeater no longer sounds distorted.

That is, after all, the primary reason you're contemplating adjusting the deviation - to work with that repeater.
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Old 27th May 2020, 3:11 pm   #12
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Default Re: Kenwood TM322. (Actually a TM-733).

I hadn't thought of using a Repeater user to set the deviation, but I have set it by comparing a sniff of its output spectrum with that from a Boefeng radio until they looked similar. This was done using a dongle/HDSDR spectrum analyser set-up. I have also used the Youtube articles re deviation and found the description of the 'disappearing carrier' method useful. A slight problem with the radio remains: on both 2m and 70cm the 733 transmits an annoying hum at the CTCSS tone frequency (I remember the previous owner saying it did this). I found a TM-733 'hum' mod on Google but it made no difference. If you look at the spectrum of the Boefeng with CTCSS switched on, the spectrum is about +/- 0.5kHz wide. The same test on the 733 produces a spectrum twice as wide, which I presume is causing the audible hum. It does this in both the 'T' (Tone) and the 'CT' mode. However, there is a test of the TONE in the manual, and I think it indicates that my radio is within spec. Does anyone recognize this problem?

Last edited by John-39; 27th May 2020 at 3:15 pm. Reason: typo
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Old 27th May 2020, 3:48 pm   #13
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Default Re: Kenwood TM322. (Actually a TM-733).

Well, as you seem to know, CTCSS actually is 'Hum', with a frequency of between about 67Hz and 250Hz, depending on the actual tone in use. It's injected onto your carrier at about 10% of the maximum voice audio level.

Since you have this problem, presumably equally, on both 70cms and 2m it sounds like the CTCSS is being injected at much too high a level / percentage. That's going on the evidence of your spectrum readings. If it was only excessive on 2m that would just suggest that the CTCSS input level on 2m needed to be reduced in similar fashion to the audio deviation.

Another thing to be aware of is that there are two types of receiver in the world, one which 'knows' about CTCSS and the other type, usually older, which doesn't. Receivers which are designed with CTCSS in mind shave off the audio frequencies below 250Hz before they are passed on to the audio amplifer and the speaker, but other receivers pass audio all the way down to 50Hz through the receiver and so anyone who is transmitting a CTCSS tone will appear to be humming. If working a net, with a wide selection of receivers listening, some of those users will complain you are transmitting a hum, others will not be able to hear it.
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Old 27th May 2020, 4:38 pm   #14
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Default Re: Kenwood TM322. (Actually a TM-733).

Just looked further at the circuit diagram dodgy-dxer linked to. There is a plug in optional CTCSS PCB but that is a red herring as it only adds CTCSS decode.

CTCSS tone for transmit seems to originate from the microprocessor on the control PCB, passes through CP401, through Filter C402/R401/C401 and then finds its way to the two 'TO' connections to other PCBs, one going to 'TO' on the VHF PCB and the other going to 'TO' on the UHF PCB. It takes similar paths on both boards after that but taking the VHF PCB as an example it goes to the top end of the deviation preset via C99 / R72.

Therefore,
-There is no preset with which the CTCSS tone level can be independently set.
-The deviation preset for each band affects both the voice deviation level for that band and the CTCSS deviation level for that band.
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Old 27th May 2020, 9:16 pm   #15
John-39
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Default Re: Kenwood TM322. (Actually a TM-733).

Thank you for your research into this. It would be interesting to know what the tone level should be before it is sent to the V/UHF PCBs, just in case there is a fault on the Control PCB. But there is a contradiction: 1) the test at the end of the Adjustments section in the manual gives a measured value that I take to be the deviation with TONE switched on: this figure is +/-0.5 to +/- 1.5 kHz, and my measurement is bang in the middle, and 2) the 'old radio' theory doesn't quite explain it because my correspondent would need an 'old' radio to hear the hum, in which case he would hear the hum on all radios, and wouldn't have commented on it. I think I'll just have to put up with it! Thanks again!
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Old 28th May 2020, 11:39 am   #16
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Default Re: Kenwood TM322. (Actually a TM-733).

I would use your SDR to look at the AF spectrum of the CTCSS hum if it allows that functionality. I think it will.

A microprocessor tone could have several harmonics which would make the ear "put back" the fundamental. Compare if you can with the Baofeng.

Maybe more filtering on the CTCSS signal from the control board is needed?
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Old 28th May 2020, 12:02 pm   #17
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Default Re: Kenwood TM322. (Actually a TM-733).

I couldn't tell just from the diagram whether what comes out of the microprocessor is digital, possibly PWM, or is analogue output from a D-A converter.

If the former, the filter formed by C402/R401/C401 won't do much to take the edges off it.
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Old 28th May 2020, 4:04 pm   #18
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Default Re: Kenwood TM322. (Actually a TM-733).

There are 7 data lines making the CTCSS output. They end up in CP401. I think that is labelled as being KRR0001. I've never heard of it and I wonder what it is?
You are right that the 2x0.01uF and 10k between them is likely to be doing little.

That is where I would try adding an extra low pass if harmonics can be seen to be the problem. I suppose the same place could also be used to control the level
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Old 28th May 2020, 4:29 pm   #19
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Default Re: Kenwood TM322. (Actually a TM-733).

The other parts beginning with 'CP' in the parts list appear to be passive component packages because they have their values stated after the circuit part number. CP401, typically, does not.

I wonder if it's a resistor ladder which generates a 'programmable' voltage output, depending on the 7-bit value being sent to it? If so the filter components would be there to iron out the little steps between one value and the next. It might be worth scoping the TO signal to see if it is a reasonable approximation of a sine wave, or not at all.
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Old 28th May 2020, 4:58 pm   #20
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Default Re: Kenwood TM322. (Actually a TM-733).

I was also thinking that but then what about R542-548, why wouldn't they have added those in it as well? Scoping the line is of course a good suggestion.
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