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John Linsley Hood FM tuner article/s
John Linsley Hood FM tuner article/s
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Old 29th July 2013, 07:11 AM   #41
HolgerHa is offline HolgerHa  Germany
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Hi DF96,

thanks for your answer.
What do you mean with "reduces HF gain" ?
I suppose you relate this to the higher frequencies of the audio range?
If so - then the difference-signal is on the very high end of the audio spectrum.
As such the deemphasis should be applied to the difference signal as well - to give the same benefit to it.
In reality it does not - deemphasis is applied to the decoded audio-signal which consists from a mixture of the mono-(sum-)signal with the difference-signal.

I agree that the noise spectrum of a mono-signal increases with the frequency and therefore the deemphasis reduces the noise volume.
But after stereo-decoding you find HF-noise mixed with (and thus transformed to) even the lowest frequencies.
This is - in my opinion - the point why deemphasis does not really make sense in stereo transmissions.

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Old 29th July 2013, 10:42 AM   #42
DF96 is offline DF96  England
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De-emphasis reduces noise, whatever the source of that noise, provided that the noise has significant HF components; that generally means white noise or noise which rises with frequency. All you need is the ability to apply the necessary pre-emphasis earlier in the chain.

For mono FM the primary source of noise is just phase noise in the transmission channel, which results in a rising noise spectrum at the receiver.

For stereo FM you get this too, but in addition there is the multiplex noise which is roughly white. De-emphasis still works. Note that de-emphasis should not be applied to the 38kHz DSB difference signal, but only the resultant audio after demodulation.
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Old 29th July 2013, 12:00 PM   #43
ivanlukic is offline ivanlukic  Serbia
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I have Denon TU660L which is great FM tuner (very close to Revox in performance but at much lower cost). But I am interested if there is some pcbs or kits for Si4735, or demo boards available?
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Old 29th July 2013, 12:12 PM   #44
DF96 is offline DF96  England
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New thread needed?
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Old 6th August 2013, 01:59 PM   #45
rsavas is offline rsavas  Canada
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Join Date: Aug 2012
Location: Ontario
Default Si4735

A new thread should have been started. But since you brought this up ...
Elektor offered a kit for Si4735, DSP radio, Project 100126 (DSP Radio) Not sure if it is still available.
I myself have none my own design using a Si4735 in a portable radio as i saw the Elektor version a bit short of being a salable product or one that meet my needs. I have also taken the original code and added a fair chunk to it, ie. RBDS PI display for North America. If you are interested send me a PM.
BTW, I am also working on using the newer Si4770 for which I am just about to get a pcb fab'd. The Si4735 is a good performer, so I predict that the Si4770 should be that much better.

Last edited by rsavas; 6th August 2013 at 02:10 PM.
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