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I need help with FM Tuner alignment
I need help with FM Tuner alignment
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Old 8th August 2018, 05:03 PM   #1
KenwoodM2A is offline KenwoodM2A  Canada
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Default I need help with FM Tuner alignment

Hello Folks!

I am looking for expert help trying to decipher some of the service manual alignment set points for my Kenwood tuners. I did take my electronic course many moons ago and have been going through some of my literature but I am still having issues in some areas as I have never done an alignment but am more than confident that I can figure it out, I'm just having a little trouble getting out of the gate!

I have 4 Kenwood tuner/receivers that I refurbished but am now at the stage where I would like to check and align the tuner section if required. I have all 4 service manuals, volt meters, a 60 Mhz scope...Yes, I know that it's not enough for FM alignment but I have a new 200 Mhz scope on it's way and should be here Friday. I also acquired a Jung Jin JSG-1101B FM/AM Stereo Signal Generator which I believe to be a Kenwood SG-5110. Both units appear to be identical and spent last weekend familiarizing myself with it's operation. It's output can be selected at dBu EMF or dBm. And yes, I did construct an impedance matching pad so I'm good to go. I also have a distortion analyzer.

The 4 units are....

Kenwood Model Eleven GX..........I LOVE this unit! The sound is so crisp and has a very warm natural sound to it!

Kenwood KT-3300d

Kenwood KT-5020

Kenwood KRC-939 ........Automobile Deck

The first thing that I would like to point out is that I don't understand why the manufacturers can't keep things simple and use actual voltages instead of using dB, dBu EMF, dBm or any other forms. All this just adds to the confusion. It is my understanding that Japan manufactures used dBu EMF but none of my manuals make reference to that. I have also been using this web site for conversions...... https://www.eeweb.com/tools/rf-unit-converter ......but without knowing for sure what they are actually using in the service manual, it complicates things a little.

My vintage Model Eleven GX from the late 70's uses dB (ANT INPUT) and makes reference in the manual that 0 dB = 1 uV.

My KT-3300d and KT-5020 from the late 80's both use dBu (ANT INPUT) with no reference.

My KRC-939 from the late 80's uses dB (ANT INPUT) with no reference.

As you can see, there is no consistency from one unit to the next as far as input levels go which is confusing.

So now let's move on to the actual alignment. This will be for the KRC-939. I have a spare unit that I marked all the pots with a fine tip marker so that I can go back in the event I screw up. I'm using this deck as a practice unit.

The first adjustment is discriminator.... input setting 98.1 Mhz, 0 dev, 60dB (ANT INPUT)......output setting DC volt meter across TP6........Tuner setting 98.1 Mhz and align T3 for 0 volt.
I had no problem getting this completed and it was very close already.

The next adjustment is Stop Level..... input setting 98.1 Mhz, 0 dev, 20dB (ANT INPUT) .....no output setting, was left blank.......Tuner setting 98.1 Mhz and adjust VR6 for Stop.

What the hell is Stop Level? I tried adjusting this pot but did not see anything change on anything.

My KT-5020 also has this alignment and says align .......To the position so that the lowest level of the S meter lights.

Next adjustment is Distortion.........input setting 98.1 Mhz, 75khz dev, 60 dB (ANT INPUT).........no output setting, was left blank.......Tuner Setting 98.1 Mhz and adjust VR9 for minimum distortion.

How am I suppose to read the distortion level? My service manual makes no metion of a distortion meter, only a volt meter and a scope on the output across speaker.

Next adjustment is Pilot Canceler........input setting 98.1 Mhz, 0 dev, Pilot : On, 60 dB (ANT INPUT)........Output Setting is Volt Meter and Scope.......Tuner setting 98.1 Mhz and adjust VR10 for minimum output.

Once again, I could not see any change on the scope as I adjusted this pot. Of course I was using my 60 Mhz scope and perhaps I need to try again with my new 200 Mhz scope once it arrives on Friday

Next adjustment is Separation.........input setting 98.1 Mhz, 1Khz +or- 68.25 Khz dev , Selector L or R, Pilot : +or- 6.75 Khz dev, 60 dB (ANT INPUT).......output setting is Volt meter and Scope.........tuner setting is 98.1 Mhz and adjust VR11 for minimum crosstalk.

I'm not sure about the Pilot : +or- 6.75 Khz dev part as far as setting my generator for this.

There are a couple more adjustments that need to be checked but we can start with this as I believe that once I figure these out with some help, the rest will all fall into place, at least I hope!
I really hope that once I get my new scope that I will be able to see what I'm suppose to be looking for cause right now I have no idea what the output is suppose to look like.

If there are any experienced tuner experts here, then I would be very grateful for any help that I can get!

Thanks!
Roland
Attached Files
File Type: pdf adjustments.pdf (496.9 KB, 16 views)
File Type: pdf adjustments3.pdf (446.4 KB, 13 views)

Last edited by KenwoodM2A; 8th August 2018 at 05:25 PM.
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Old 8th August 2018, 08:21 PM   #2
Bill_P is offline Bill_P  United States
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For all four units 0dB=1uV (dBu). Then 20dB=10uV and 60dB=1000uV.

Stop level is probably the minimum signal level to stop an autoscan of the band.

Distortion is measured on a THD meter or spectrum analyzer. Gross distortion can be seen on an oscilloscope. Leave this adjustment alone if you do not have equipment to measure distortion.

Pilot canceller is a 19kHz notch filter to remove the pilot signal from the output. There is always some residual 19kHz pilot signal left in the audio output but it should be quite small when the filter is adjusted properly.

Generator pilot deviation should be 9% of the total 75kHz deviation of the test signal from what you posted. Does the generator have a way to adjust the pilot amplitude (deviation)?

A 60MHz scope should be quite adequate for the adjustments you asked about.
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Old 8th August 2018, 08:39 PM   #3
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by KenwoodM2A View Post
The first thing that I would like to point out is that I don't understand why the manufacturers can't keep things simple and use actual voltages instead of using dB, dBu EMF, dBm or any other forms.
At least for FM car radios, dBuV EMF is pretty standard nowadays. Silly, because almost any non-broadcast receiver uses dBm - which gives you more meaningful results when you compare receivers meant for different antenna (aerial) impedances.

Quote:
Originally Posted by KenwoodM2A View Post
The first adjustment is discriminator.... input setting 98.1 Mhz, 0 dev, 60dB (ANT INPUT)......output setting DC volt meter across TP6........Tuner setting 98.1 Mhz and align T3 for 0 volt.
I had no problem getting this completed and it was very close already.
OK, so far so good!

Quote:
Originally Posted by KenwoodM2A View Post
The next adjustment is Stop Level..... input setting 98.1 Mhz, 0 dev, 20dB (ANT INPUT) .....no output setting, was left blank.......Tuner setting 98.1 Mhz and adjust VR6 for Stop.

What the hell is Stop Level? I tried adjusting this pot but did not see anything change on anything.
Is there an automatic transmitter searching function? If so, then this is probably the minimum level at which it stops searching.

Quote:
Originally Posted by KenwoodM2A View Post
Next adjustment is Distortion.........input setting 98.1 Mhz, 75khz dev, 60 dB (ANT INPUT).........no output setting, was left blank.......Tuner Setting 98.1 Mhz and adjust VR9 for minimum distortion.

How am I suppose to read the distortion level? My service manual makes no metion of a distortion meter, only a volt meter and a scope on the output across speaker.
Yes, for this one you need a distortion meter (or very good ears).

Quote:
Originally Posted by KenwoodM2A View Post
Next adjustment is Pilot Canceler........input setting 98.1 Mhz, 0 dev, Pilot : On, 60 dB (ANT INPUT)........Output Setting is Volt Meter and Scope.......Tuner setting 98.1 Mhz and adjust VR10 for minimum output.

Once again, I could not see any change on the scope as I adjusted this pot. Of course I was using my 60 Mhz scope and perhaps I need to try again with my new 200 Mhz scope once it arrives on Friday
What you are looking for and trying to minimize, are 19 kHz residues on the audio outputs. You don't need a 200 MHz scope for that, in fact, the smaller the bandwidth, the less the 19 kHz residue is obscured by the scope's noise.

Quote:
Originally Posted by KenwoodM2A View Post
Next adjustment is Separation.........input setting 98.1 Mhz, 1Khz +or- 68.25 Khz dev , Selector L or R, Pilot : +or- 6.75 Khz dev, 60 dB (ANT INPUT).......output setting is Volt meter and Scope.........tuner setting is 98.1 Mhz and adjust VR11 for minimum crosstalk.

I'm not sure about the Pilot : +or- 6.75 Khz dev part as far as setting my generator for this.
6.75 kHz peak deviation is the nominal level for an FM pilot tone. If your generator doesn't allow you to adjust it, it is probably 6.75 kHz by default. In any case, unless there is something very wrong with the radio, any level between 6 kHz and 7.5 kHz peak deviation should give essentially the same result.

Instead of playing a 1 kHz tone through one channel (left, for example) of the signal generator and adjusting for minimum signal at the other channel (right) of the receiver, you could also play your favourite music through the left channel of the signal generator and adjust by ear for minimum audio on the right channel receiver output. That makes the adjustment more meaningful for normal audio. (This is assuming that there is only one adjustment for channel separation, not several that need to be done with different modulation frequencies.)

Last edited by MarcelvdG; 8th August 2018 at 08:57 PM. Reason: Singular verb that should have been plural.
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Old 8th August 2018, 08:55 PM   #4
MarcelvdG is offline MarcelvdG  Netherlands
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By the way, stop level is an exception, but for most of these adjustments, the precise RF level doesn't matter much. You just need a signal large enough for good full stereo reception, yet small enough not to blow up the radio.
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Old 8th August 2018, 09:15 PM   #5
scott wurcer is offline scott wurcer  United States
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I have not done it in years, but I used to align directly from the schematic trying to figure out (usually easy) exactly what each trim does. The distortion can be trimmed pretty well by eye if you have an FM sweep generator in the 100Mhz range. You trim the detector slope to be as symmetrical as possible and as straight as possible through 0. Never had any fancy instruments.

There are some ham techniques online for optimizing the front end if you need to do that.
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Old 9th August 2018, 01:47 AM   #6
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by Bill_P View Post
For all four units 0dB=1uV (dBu). Then 20dB=10uV and 60dB=1000uV.
I would would be nice if that was the actual reference. Still makes me wonder why Kenwood would make a FM Stereo generator to align tuners using dBu EMF or dBm as an output selection but yet use dBu=1uV as a reference in their own service manual. The dBu=1uV was only referenced in the manual for the Model Eleven GX which was a model from the late 70's and the other models are from the late 80's.
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Old 9th August 2018, 01:59 AM   #7
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by Bill_P View Post
For all four units 0dB=1uV (dBu). Then 20dB=10uV and 60dB=1000uV.

Stop level is probably the minimum signal level to stop an autoscan of the band

Distortion is measured on a THD meter or spectrum analyzer. Gross distortion can be seen on an oscilloscope. Leave this adjustment alone if you do not have equipment to measure distortion.

Pilot canceller is a 19kHz notch filter to remove the pilot signal from the output. There is always some residual 19kHz pilot signal left in the audio output but it should be quite small when the filter is adjusted properly.

Generator pilot deviation should be 9% of the total 75kHz deviation of the test signal from what you posted. Does the generator have a way to adjust the pilot amplitude (deviation)?

A 60MHz scope should be quite adequate for the adjustments you asked about.
Stop level sounds right.

As far as distortion goes, I do have a distortion analyzer but the service manual makes no mention of how or where to connect so I'm a little unsure about this.

My generator does allow to set the Pilot level from 0-15%
Is 9% the norm?
The manual does not mention what % level to set the Pilot
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Old 9th August 2018, 02:11 AM   #8
Bill_P is offline Bill_P  United States
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dBu is shorthand for dB with respect to 1uV. dB is always a relative quantity and all your tuners are referenced the same.

The distortion meter would connect to the tuner audio output. Hopefully in the case of the car stereo, the power amplifier does not swamp the tuner distortion. If it does, measure further back in the audio chain like at the volume control.

Pilot levels between 8 and 10% are normal.
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Old 9th August 2018, 02:44 AM   #9
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by MarcelvdG View Post
Is there an automatic transmitter searching function? If so, then this is probably the minimum level at which it stops searching.

Yes there is so thats probably correct



Quote:
Originally Posted by MarcelvdG View Post
Yes, for this one you need a distortion meter (or very good ears).
I do have a distortion analyzer but the manual makes no reference of one being used for the adjustment or does it even mention one other than a volt meter and a scope.



Quote:
Originally Posted by MarcelvdG View Post
What you are looking for and trying to minimize, are 19 kHz residues on the audio outputs. You don't need a 200 MHz scope for that, in fact, the smaller the bandwidth, the less the 19 kHz residue is obscured by the scope's noise.
I'm not sure what I'm suppose to be looking for on the scope. I noticed no change on my scope when I tried to adjust. I should have seen something different.



Quote:
Originally Posted by MarcelvdG View Post
6.75 kHz peak deviation is the nominal level for an FM pilot tone. If your generator doesn't allow you to adjust it, it is probably 6.75 kHz by default. In any case, unless there is something very wrong with the radio, any level between 6 kHz and 7.5 kHz peak deviation should give essentially the same result.
Ok, now I get it! My generator displays it in percentage so 9% level setting on my generator is the same as 6.75khz
9% of 75 khz = 6.75 khz


Quote:
Originally Posted by MarcelvdG View Post
Instead of playing a 1 kHz tone through one channel (left, for example) of the signal generator and adjusting for minimum signal at the other channel (right) of the receiver, you could also play your favourite music through the left channel of the signal generator and adjust by ear for minimum audio on the right channel receiver output. That makes the adjustment more meaningful for normal audio. (This is assuming that there is only one adjustment for channel separation, not several that need to be done with different modulation frequencies.)

That's a good idea! So I can use the left or right external input connections to feed a signal into the generator like my distortion analyzer for example?
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Old 9th August 2018, 03:25 AM   #10
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by KenwoodM2A View Post
I do have a distortion analyzer but the manual makes no reference of one being used for the adjustment or does it even mention one other than a volt meter and a scope.
It's silly that they forgot to mention that you need one, but anyway, as Bill already wrote, its input has to be connected to an audio output of the tuner. The signal generator has to be modulated with a low-distortion sine wave.


Quote:
Originally Posted by KenwoodM2A View Post
I'm not sure what I'm suppose to be looking for on the scope. I noticed no change on my scope when I tried to adjust. I should have seen something different.
When the pilot tone of the signal generator is on, but otherwise there's no modulation, you should see a very small 19 kHz signal at the audio outputs of your tuner. If you don't, I have no idea why not. By the way, the pilot level for this adjustment has to be precisely 9 %.

Do you use a 1:1 passive probe, with the scope set to 1 Mohm input resistance and limited bandwidth? Can you maybe use your distortion analyser as a selective voltmeter?

Quote:
Originally Posted by KenwoodM2A View Post
Ok, now I get it! My generator displays it in percentage so 9% level setting on my generator is the same as 6.75khz
9% of 75 khz = 6.75 khz
Exactly!

Quote:
Originally Posted by KenwoodM2A View Post
That's a good idea! So I can use the left or right external input connections to feed a signal into the generator like my distortion analyzer for example?
I don't know your FM stereo signal generator, but usually you can feed in an external modulating signal.

Last edited by MarcelvdG; 9th August 2018 at 03:28 AM.
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