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I need help with FM Tuner alignment
I need help with FM Tuner alignment
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Old 10th August 2018, 02:33 AM   #11
KenwoodM2A is offline KenwoodM2A  Canada
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Thanks to all you guy's so far! This info has helped a lot!
My distortion meter/analyzer has an output and input feed and my generator has a left and a right external input feed and an output.
I was not aware that in order to use a distortion meter, that I would need to feed a an output from the distortion meter, into the signal generator, through the tuner and then back to the input of the distortion meter.

Is this how all distortion meters work? Or are there some distortion meters that only require an input from the source to detect the distortion level???
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Old 10th August 2018, 02:47 AM   #12
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by Bill_P View Post
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.
i'm not using a power amp. I have my connection directly on the audio out RCA's of the tuner.

It seems a Pilot level of 9% is the correct number that I need.
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Old 10th August 2018, 03:37 AM   #13
PRR is online now PRR  United States
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Quote:
Originally Posted by KenwoodM2A View Post
......are there some distortion meters that only require an input from the source to detect the distortion level???
That can work.

But what is this "source"? A low-price FM generator may have a 7-cent audio oscillator with 5% THD, and maybe at 876Hz instead of 1KHz.

Yes, you can detect distortion by taking *both* the raw source and the "received" signal. But if the source distortion is not small, uncertainties pile up.

The Usual Way To Measure Distortion is to put a low-THD oscillator to the Unit Under Test and analyze the output. The oscillator and analyzer may be sold together, or separate, even different makes as long as they are good.

The only difference here is that your Unit Under Test is necessarily an audio-to-FM converter and an FM-to-audio receiver, together. And the two THDs do combine. So until the FM Generator is certified low-THD, you can't get the true THD of the receiver alone. However in this case you just want *lowest* THD as you turn a slug in the receiver. While a high-THD FM-Gen would mask the depth of the lowest THD, you will also rock around that point to see where THD come up. Split the difference and that really should be "optimum", or so close you'll never mind. (If the THD-vs-slug relation is very asymmetrical, something is broke.)

_I_ think these meter-tests are for first set-up, and for when the repair tech must work in a steel cellar. Particularly STOP.... put it on your usual antenna and hit Scan. If Stop is too low, it stops at any slight noise. If too high, it never stops, or only for a tower you can see from your window. The "ideal" setting is so it gets all your usable signals and skips most of the too-weak and just-noise channels. Likewise Distortion "can" be trimmed by tuning a good signal, really centered, then rocking the slug until signal garbles, back until it garbles again, and centering the slub between those two limits.

Last edited by PRR; 10th August 2018 at 03:42 AM.
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Old 10th August 2018, 05:24 AM   #14
MarcelvdG is offline MarcelvdG  Netherlands
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If the FM signal generator has a distortion in the same order as the receiver or worse, the whole distortion trimming procedure becomes dubious, because minimum distortion may then mean that the receiver's distortion cancels as much as possible of the FM signal generator's distortion.
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Old 11th August 2018, 02:19 AM   #15
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by PRR View Post
That can work.

But what is this "source"? A low-price FM generator may have a 7-cent audio oscillator with 5% THD, and maybe at 876Hz instead of 1KHz.

Yes, you can detect distortion by taking *both* the raw source and the "received" signal. But if the source distortion is not small, uncertainties pile up.

The Usual Way To Measure Distortion is to put a low-THD oscillator to the Unit Under Test and analyze the output. The oscillator and analyzer may be sold together, or separate, even different makes as long as they are good.

Ok, this is what I have......

Amber 3501 distortion and noise analyzer from 1988.
internal oscillator output 10 Hz to 50 khz .003% THD
50 Hz to 5 Khz .0008% THD

Kenwood SG-5110 Am/Fm stereo generator
Distortion Factor 0.05% or less (RF: 10.7Mhz, 76 Mhz - 110Mhz )

Could I just simply use the 1Khz or 400 Hz modulated frequency of the generator and hook the distortion meter at the rca output of the tuner to check distortion?
Or should I use the use the internal oscillator of the distortion meter, feed into the external input of the generator and then check the distortion with the input of the distortion meter connected to the rca output of the tuner?


Quote:
Originally Posted by PRR View Post
The only difference here is that your Unit Under Test is necessarily an audio-to-FM converter and an FM-to-audio receiver, together. And the two THDs do combine. So until the FM Generator is certified low-THD, you can't get the true THD of the receiver alone. However in this case you just want *lowest* THD as you turn a slug in the receiver. While a high-THD FM-Gen would mask the depth of the lowest THD, you will also rock around that point to see where THD come up. Split the difference and that really should be "optimum", or so close you'll never mind. (If the THD-vs-slug relation is very asymmetrical, something is broke.)
That make sense to me....
Attached Images
File Type: jpg Amber3501A.jpg (88.1 KB, 57 views)
File Type: jpg kenwood SG-5110.jpg (50.8 KB, 56 views)

Last edited by KenwoodM2A; 11th August 2018 at 02:32 AM.
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Old 11th August 2018, 02:21 AM   #16
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by MarcelvdG View Post
If the FM signal generator has a distortion in the same order as the receiver or worse, the whole distortion trimming procedure becomes dubious, because minimum distortion may then mean that the receiver's distortion cancels as much as possible of the FM signal generator's distortion.

That makes total sense to me!!
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Old 11th August 2018, 05:21 AM   #17
MarcelvdG is offline MarcelvdG  Netherlands
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My guess would be that the distortion trimming becomes somewhat more accurate when you use the distortion analyzer's oscillator. I can't say by how much, though, because Kenwood doesn't specify how much of the 0.05 % distortion comes from their VCO and how much from their low-frequency oscillator.
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Old 13th August 2018, 01:31 AM   #18
KenwoodM2A is offline KenwoodM2A  Canada
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I had some good luck today!
Played around with my distortion meter and my new scope. After several hours of getting to know both of these units, I was finally able to figure out how to check and adjust my distortion level. The tuner was actually close but was able to tweak it a little better.
My Amber distortion meter works like a charm and has some really nice features and some awesome specs!. Was well worth the money, although I did not spend much for it!
Now I just need to pick up some extra bnc cables and continue experimenting till I can do this with my eyes closed!
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