John Linsley Hood FM tuner article/s

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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.
Regards

HH
 
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.
 
Si4735

Yes,
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.
Rick
 
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I've restarted this in the hope that someone could share the assembly instructions for the Hart Electronics kit. Via two separate ebay purchases I now have the Hart tuner without the AM section, and the complete AM section, both of which work. My wish would be to fit the AM boards into the FM chassis to produce a complete AM/FM unit. I can see how the power supply & tuner head would be connected, but without those instructions it will be difficult to figure out how the band switching is done and how the audio outputs from the two sections are combined. Any help would be most welcome.
 
Bespoke Constructor
Joined 2006
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this is the ETI magazine that I have ... but will check again to make sure for you
 

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Thanks for the offer, but I've already found the ETI issues from 1987 which cover the FM tuner, and also the WW articles from 1986 for the synchrodyne AM tuner. These are great for understanding how the two separate receivers work. I'm hoping to find the Hart Electronics build instructions for the kit they marketed which included both of these but integrated into a common chassis. The Hart unit I bought on eBay has just the FM section installed, and although there is obviously provision for AM, it isn't immediately clear how the synchrodyne pcbs are hooked up, which those instructions should hopefully explain.
 
Bespoke Constructor
Joined 2006
Paid Member
Thanks for the offer, but I've already found the ETI issues from 1987 which cover the FM tuner, and also the WW articles from 1986 for the synchrodyne AM tuner. These are great for understanding how the two separate receivers work. I'm hoping to find the Hart Electronics build instructions for the kit they marketed which included both of these but integrated into a common chassis. The Hart unit I bought on eBay has just the FM section installed, and although there is obviously provision for AM, it isn't immediately clear how the synchrodyne pcbs are hooked up, which those instructions should hopefully explain.

Ok fully understand ... I will keep a look out for you as you have me intrigued now :)
 
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