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question about an AM demodulator IC ?

Thread starter #1
hello guys

i found in my electronics salvage an old ic its a TDA3845 when i searched for it and looked at the datasheet i saw that its
a Quasi split-sound circuit and AM demodulator .
so my question is :

1- what is Quasi split mean ??
2- i was wondering can i use it to make an AM or FM radio or something ?

i saw a circuit for the ic and its seems very simple

so what exactly is it (it seems more like a radio to me ) ?
 
Last edited:

JimB

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Most Helpful Member
#2
1- what is Quasi split mean ??
Quasi Split Sound is a way of describing the NICAM stereo transmission system.
From Wikipedia:
Near Instantaneous Companded Audio Multiplex (NICAM) is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks.[1] In the 1980s, broadcasters began to use NICAM compression for transmissions of stereo TV sound to the public.
For more information, look at the link:
https://en.wikipedia.org/wiki/NICAM


2- i was wondering can i use it to make an AM or FM radio or something ?
Yes, that should be possible.

JimB
 
Thread starter #3
thanks jimB .

so the ic was designed to receive NICAM packet audio transmission for the tv ?
so most of the tv audio transmisstion is NICAM ? and is there a radio broadcasts using the same protocol ?
can i use that to receive tv brodcasts (the sound only ) ?


and how i will modify it to receive AM ?
so i have to make a local oscillator and mixer circuit to produce the IF then feed it to the ic
and change the LC thank circuit for AM ?or what

sorry i have a lot of questions :), i realy appreciate your help
 

JimB

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Most Helpful Member
#4
so most of the tv audio transmisstion is NICAM ?
In the UK, analogue UHF TV had nicam stereo sound.
The basic TV sound signal was FM, the nicam part made it into stereo for receivers which were equipped to decode it.
All UK TV is now digital, the analogue and NICAM are gone.

and is there a radio broadcasts using the same protocol ?
Not in the UK.

can i use that to receive tv brodcasts (the sound only ) ?
Yes, I think so.

and how i will modify it to receive AM ?
Maybe use the AM output from the chip?
I don't know.

so i have to make a local oscillator and mixer circuit to produce the IF then feed it to the ic
Yes.

and change the LC thank circuit for AM ?or what
If you mean Medium Wave (550 to 1600kHz), yes.

JimB
 
Thread starter #5
thank you so much

i will try the circuit above with a local oscillator and the mixer and see what will happen . wish me luck:)
 
Thread starter #10
The one in the datasheet - the circuit that makes the IC work!!.
iam sorry i thought you ment the circuit above .
actualy i connected an internal (oscillator - mixer - IF amp ) from another ic i have to the TDA3845 theoreticly it should work
but it didnt i heared just a hissing sound !?


iam sorry but why my previos comment has changed:cool: i dindt mean any thing just was asking !?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#11
I don't really see why you're playing with this chip, it's NOT a radio chip, it's a TV one.

It 'might' be possible to use some parts of it to help build a radio?, but it's likely to be pretty difficult as there won't be any data out there about doing so.
 
Thread starter #12
I don't really see why you're playing with this chip, it's NOT a radio chip, it's a TV one.

It 'might' be possible to use some parts of it to help build a radio?, but it's likely to be pretty difficult as there won't be any data out there about doing so.
you are propaply right , but i thougt it would be very cool if i had a tv sound broadcast receiver .
but propaply its easier to just wach the tv .
 
Thread starter #14
But you wouldn't, analogue TV ended a while back.
me :can i use that to receive tv brodcasts (the sound only ) ?
JimB: Yes, I think so.

"i think so " from JimB ,
gave me a little motivation to try the circuit , but no problem ( building and experimenting with radio circuit is one of my true passions )
 

JimB

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Most Helpful Member
#15
me :can i use that to receive tv brodcasts (the sound only ) ?
JimB: Yes, I think so.
Yes, I did say that didn't I.

But, you have to use all the appropriate parts:
Signal frequency tuned circuits and an RF amplifier to give the required sensitivity.
A mixer and local oscillator to convert the signal frequency to the intermediate frequency.
A suitable IF filter to give the required selectivity.
An audio amplifier to give enough power to drive the loudspeaker.

JimB
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#16
Yes, I did say that didn't I.

But, you have to use all the appropriate parts:
Signal frequency tuned circuits and an RF amplifier to give the required sensitivity.
A mixer and local oscillator to convert the signal frequency to the intermediate frequency.
A suitable IF filter to give the required selectivity.
An audio amplifier to give enough power to drive the loudspeaker.
And how does all that decode the digital TV signals?.

However, he's now mentioned (elsewhere?) that he's in Egypt, and I've no idea if they have gone digital or not?.
 

JimB

Super Moderator
Most Helpful Member
#17
And how does all that decode the digital TV signals?.
It does not, I never said that it would.
Have a look at post #4 of this thread for my best attempts to give a positive/definitive reply to the OPs questions which may have lead to some experimentation for him, rather than a wet blanket "Oooh, you can't do that!" kind of reply.

However, he's now mentioned (elsewhere?) that he's in Egypt, and I've no idea if they have gone digital or not?.
Neither do I.

By the way, I had sussed out that he was in Egypt right at the start.

JimB
 

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