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Old 23rd Apr 2024, 1:15 pm   #41
svetolik
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Well maybe digging the obsolete are more precise words in modern terms.
Signal meter works what is not case with tuning meter and activating AFC cause mess with frequency but there is no urgent need for such because I can hear a peace of hair if it is out of tune and now precise mode for tuning is spot on with frequency of station.. Automatic mode?
And is someone familiar with FM distortion?
It is very interesting area.

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Old 23rd Apr 2024, 2:54 pm   #42
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

The coils (whatever their value) and the capacitors (whatever their value) need to be resonant at close to 10.7MHz, then a final fine adjustment of the slugs should be able to get the quadrature detector working linearly.

A grid-dip oscillator with something to check its frequency would have been the old-fashioned way.

A sig gen to apply a signal and a scope to monitor the response with care over very light coupling would do the job.

One of those little VNAs, again with only light coupling through large value resistors would be a modern way.

But it does need something more than a multimeter.

The task isn't so much doing the job as trying to do it with whatever equipment is available.

The FM demodulator is nothing more than a mixer. Inside the chip is what's usually called a Gilbert Cell mixer. The IF signal drives one input port directly, and, via the phase shift coil network, it also drives the other input port.

The output port is DC coupled and makes the DC voltage for AFC and the tuning meter. THe AC component is your multiplex audio redy to be fed to your multiplex decoder.

If you have a signal generator, set up a centre-zero 100uA meter where the diagram shows the tuning meter and swing the sig gen across 10.7MHz. As you approach the right frequency, the meter should jump away from the centre zero position ot one side or the other. Then it should move gently across to a similar amount of deflection on the other side of zero before jumping back to zero.

If your tuner already has a tuning meter, this is what it should show and it saves you the fuss of rigging one up. The middle of the linear portion should be at the centre of the IF filters' passband.

From your description, something is so far off that the discriminator is offset out of range of the IF. That comes down to the phase shift tuned circuit. Broken capacitor maybe? or corroded?

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Old 23rd Apr 2024, 3:10 pm   #43
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

From your description, something is so far off that the discriminator is offset out of range of the IF. That comes down to the phase shift tuned circuit. Broken capacitor maybe? or corroded?

David[/QUOTE]


What I did not understand is attenuation when is ref voltage on the TP1 is near 0V on to Nikko tuner.

It should be opposite with getting stereo signal according to manual?
Is it possible that resonance is such shifted far off what causes this behavior?


Now I have managed stereo signal on to another tuner Dual, with implemented LA1235 but that is another part.
I will force decoder from Nikko with both signals pilot and composite from Dual LA1235 in order to get best of those young mummies.
I do not have signal generator and oscilloscope but it is interesting anyway.

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Old 23rd Apr 2024, 4:04 pm   #44
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Here is a schematic of Dual CT1640.
I would like to hear more about its front end.
It looks like 7 LC resonance circuits without amplification between what I consider as better from my basic knowledge and intuition.
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Old 23rd Apr 2024, 7:35 pm   #45
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Quote:
Originally Posted by Radio Wrangler View Post



The FM demodulator is nothing more than a mixer. Inside the chip is what's usually called a Gilbert Cell mixer. The IF signal drives one input port directly, and, via the phase shift coil network, it also drives the other input port.

The output port is DC coupled and makes the DC voltage for AFC and the tuning meter. THe AC component is your multiplex audio redy to be fed to your multiplex decode





David
That multiplex audio line is only one needed for stereo decoding?
I see on LA3401 PLL decoder from Nikko tuner pin 17 for pilot detection separate from FM in pin.
Should I just feed pin 17 LA3401 with line from Nikko that is connected now from pin 7 of LA1235 drom Dual in order to get decoded stereo signal on to Nikko tuner too?
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Old 23rd Apr 2024, 11:19 pm   #46
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

That multiplex audio line is needed for mono or stereo reception, and needs to be reasonably low distortion for both
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Old 24th Apr 2024, 8:05 am   #47
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Quote:
Originally Posted by Julesomega View Post
That multiplex audio line is needed for mono or stereo reception, and needs to be reasonably low distortion for both
Distortion is unlikely issue here because I can hear less distorted sound from recorded broadcast than when is it live speech on air from studio.
It is old national radio station with dying equipment, worse garbage than mine, but when they takeover live broadcast from Metropolitan opera it feels like light spring wind, music just coming to head, reach and detailed what is sign of less distortion that usually covers that quiet passages or low signals.
I need just to clear that pilot signal on the input of PLL decoder, is that pilot for stereo decoding or one more reference signal?
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Old 24th Apr 2024, 1:04 pm   #48
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

The pilot is a 19 kHz frequency which is used to reconstitute by frequency doubling the 38 kHz carrier necessary to demodulate the difference channel (L-R) AM modulated at 38 kHz with suppressed carrier.
Combining L+R and L-R permits to recover L and R channels of a stereo transmission.
This for "conventrional" stereo decoders.
PLL decoders generally use an oscillator running at 76 kHz ( 4 x 19 kHz) locked on the 19 kHz pilot.

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Old 24th Apr 2024, 1:49 pm   #49
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Than I assuming that pilot 19 kHz on the LA3081 is output, "VCO stop", perhaps part of muting function, as it is marked like "19kHz output" on the MC310 decoder from Dual that is not PLL and have half less pins.
I get one LA3081 more, muting do not work on the Dual anyway so there is a chance to dance together.
Voltages on the signal pins for stereo indication are different and I have to look for right voltage source.
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Old 27th Apr 2024, 12:42 pm   #50
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Finally got that Dunikko stereo signal, now playing from LA1235 implemented in Dual tuner and connected to the LA3401 PLL decoder on to Nikko tuner.
The quality of sound is with more details and more mid bass energy, but I cant measure it. and confirm anything precise.
There is indication for stereo signal on the Nikko without any signal strength indication.
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Old 27th Apr 2024, 12:51 pm   #51
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

There is a detector looking for the 19kHz pilot tone. If the pilot tone is absent, the stereo decoder switches into mono mode. This enables smaller signals to be played with less noise than if the decoder was left trying to function unlocked. It also switches the stereo light on if 19kHz is detected strongly enough.

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Old 27th Apr 2024, 1:09 pm   #52
svetolik
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Default Re: Nikko NT 950 Tuner, no stereo, low level mono output.

Thanks, it is black boxes businesses theses days. I cant reach individual components, so not much fun here thus it is over engineered with function that I don't need but low distortion is real point here and must have performance.
It will be a reference for my backing to tubes roots.
Hope that you will find interest to comment further. I think that one thread with steps showed how to handle linearity and distortion will be of interest too.
I am listen only two radio stations, so I am ready to implement crystal oscillators too.
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