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How does a "modern" radio work?

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OY! FM is frequency modulation ... the error signal in a PLL is used to change the VCO to "match" the carrier frequency ... In other words the the error signal IS the demoulated audio if you are talking mono... stereo obviously requires an addition step

You don't track the modulation in the tuning, you do the de-modulation after it's been amplified down the IF, if you could track the tuning modulation almost none of the radio stages would be required.
 
You don't track the modulation in the tuning, you do the de-modulation after it's been amplified down the IF, if you could track the tuning modulation almost none of the radio stages would be required.

again FM IS FREQUENCY MODULATION ... the difference between the carrier and the modulation IS the error signal ... IF helps for selectivity but it works the same error signal to mixer to IF filter. PLL on the IF output STILL demodulates the RF for you. The error signal voltage is proportional to the difference in frequency, and the difference in frequency IS the original modulation signal!
 
again FM IS FREQUENCY MODULATION ... the difference between the carrier and the modulation IS the error signal ... IF helps for selectivity but it works the same error signal to mixer to IF filter. PLL on the IF output STILL demodulates the RF for you. The error signal voltage is proportional to the difference in frequency, and the difference in frequency IS the original modulation signal!

I'm fully aware of exactly how FM works.

Perhaps you would care to post a link to a radio that works in your imagined fashion?, using the RF PLL tuning as a demodulator as well.
 
I'm fully aware of exactly how FM works.

Perhaps you would care to post a link to a radio that works in your imagined fashion?, using the RF PLL tuning as a demodulator as well.

well then you must fully comprehend it and i should not have to waste my time explaining to you that an error signal proportional to a difference in frequency is the original FM modulation then, should I?
 
I'm fully aware of exactly how FM works.

Perhaps you would care to post a link to a radio that works in your imagined fashion?, using the RF PLL tuning as a demodulator as well.

[SARCHASM] Oh I'm so sorry, I forgot: you are a god and we are all peons not worthy to worship at your feet![/SARCHASM]

would you perchance believe a resource for electronics engineers? Or is it wrong as well since it agrees with me?

**broken link removed**
 
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Refer to post #17, and all my posts since - keeping repeating the same pointless line in meaningless - as I said please show us ONE radio which does what you suggest (or why don't you build one to show us?).
 
Refer to post #17, and all my posts since - keeping repeating the same pointless line in meaningless - as I said please show us ONE radio which does what you suggest (or why don't you build one to show us?).

figures ... i did not expect you to believe an actual document anymore than you believe me ... seems basic theory is meaningless to you ... even verified tech journals don't cut it ... doesn't really surprise me given your history ...

I suppose this one will be a little easier for a person of your apparent IQ to comprehend:

PLL FM Demodulator | Circuit Diagram
 
figures ... i did not expect you to believe an actual document anymore than you believe me ... seems basic theory is meaningless to you ... even verified tech journals don't cut it ... doesn't really surprise me given your history ...

I suppose this one will be a little easier for a person of your apparent IQ to comprehend:

PLL FM Demodulator | Circuit Diagram

What are you on about?, that's what I've been saying all along - a PLL after the IF demodulating the FM.

Are you now changing your mind?, or are you just confused about what you think the PLL in that circuit is doing (it's FM demodulation, NOT PLL tuning).
 
What are you on about?, that's what I've been saying all along - a PLL after the IF demodulating the FM.

Are you now changing your mind?, or are you just confused about what you think the PLL in that circuit is doing (it's FM demodulation, NOT PLL tuning).

not changing my mind at all... it is both ... if i mix that 10KHz carrier with a 12KHz carrier the PLL would happily lock onto the 10KHz carrier.
 
The TDA7000 converts the RF at 100Mhz (ish) to an IF of 70khz.
The demodulation (using a PLL, the datasheet calls it an FLL, Frequency Locked Loop) takes place at a low frequency 70khz, not 100Mhz.

In a receiver of reasonable performance, the incoming RF is converted to the IF using an oscillator whos frequency is determined by a phase locked loop.
Demodulation of the FM can take place at the IF frequency usin a variety of methods, one of which is a phase locked loop.

Demodulation of the off-air signal at 100Mhz is not practical in a radio receiver.
It may be quite possible to build one, but its performance will be limited.

JimB
 
The TDA7000 converts the RF at 100Mhz (ish) to an IF of 70khz.
The demodulation (using a PLL, the datasheet calls it an FLL, Frequency Locked Loop) takes place at a low frequency 70khz, not 100Mhz.

In a receiver of reasonable performance, the incoming RF is converted to the IF using an oscillator whos frequency is determined by a phase locked loop.
Demodulation of the FM can take place at the IF frequency usin a variety of methods, one of which is a phase locked loop.

Demodulation of the off-air signal at 100Mhz is not practical in a radio receiver.
It may be quite possible to build one, but its performance will be limited.

JimB

again ... it is not difficult at all to control a premixer VCO with a post filter phase comparison. a single PLL performs the channel selection as well as the demodulation using generic inexpensive IF filters
 
I guess I don't understand what a detector is then. The audio comes from the same demodulator as does the voltage which tunes the one and only local oscillator. After a high pass filter it is audio; the same signal passes through a low pass filter to perform VCO tuning.
 
I guess I don't understand what a detector is then. The audio comes from the same demodulator as does the voltage which tunes the one and only local oscillator. After a high pass filter it is audio; the same signal passes through a low pass filter to perform VCO tuning.

well i think you have the high pass and low pass backwards.... there are numerous ways of doing things... technically the "PLL" is a detector for FM and includes everything inside the control loop. that could conceivably be the PLL VCO for an intermediate IF local osc through a filter and a second fixed local osc through a filter to the PLL phase comparator. I do not know off hand if an FM stereo coded signal would pass through a generic 455KHz AM IF filter, though that would be convenient.
 
well i think you have the high pass and low pass backwards.... there are numerous ways of doing things... technically the "PLL" is a detector for FM and includes everything inside the control loop. that could conceivably be the PLL VCO for an intermediate IF local osc through a filter and a second fixed local osc through a filter to the PLL phase comparator. I do not know off hand if an FM stereo coded signal would pass through a generic 455KHz AM IF filter, though that would be convenient.

No it wouldn't, it's much topo narrow a bandwidth, which is why 10.7MHz is used (and to give better image rejection of course). It's also why the TDA7000 is nothing but a toy, it's much too low an IF.
 
My apologies, I meant the TDA7088. 7800 doesn't appear to exist.

I recommend review of the TDA7088 diagram before maintaining that the VCO and audio outputs are driven by separate detectors/demodulators.... the data sheet is very clear.

Page 3, Figure 1.
 

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The TDA7088 is used in the poor performance "FM radios" from The Dollar Store. The radio is actually free because the $1.00 pays for the boat trip from China, the battery and the headphones. Some come with a flashlight (torch) built-in.

I recently got two of these garbage radios for free. They came with dead batteries. When I replaced their button battery cells, they scan then pickup only stong local stations. They sound awful.
 
My apologies, I meant the TDA7088. 7800 doesn't appear to exist.

I recommend review of the TDA7088 diagram before maintaining that the VCO and audio outputs are driven by separate detectors/demodulators.... the data sheet is very clear.

Indeed it is:

The circuit contains a
frequency-locked-loop (FLL) system with an Intermediate
Frequency (IF) of about 70 kHz.

Exactly as we've said all along, demodulation after the IF - and that IC doesn't even use PLL tuning.
 
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