Kerim
Member
When I was at the university about 37 years ago (end of 70’s) I used reading/hearing:
Recovering the modulating signal of a double sideband suppressed carrier signal is much harder than of a SSB-SC one.
But on the other hand, it sounded rather illogical, to me in the least, that receiving two sidebands (symmetrical) could be worse than receiving just one of them!
So, as an MS thesis, I designed and built (after many failures during about 5 months) a simple low-cost linear demodulator for DSB-SC.
Its mains components were:
1 LM339 comparator IC
1 CD4046 a PLL IC
1 CD4013 as flip-flop
1 CD4066 CMOS switches
Obviously, it works for any AM index; from m=0 (carrier with no modulation) to infinity (DSB-SC) while it has a frequency lock range (a PLL characteristic), as the AFC in FM receivers.
Also, being a synchronous AM demodulator, it is suitable for recovering hi-fi audio signals as well (as long the receiver bandwidth is wide enough).
And, if necessary, its components could be integrated in one low cost IC.
But, due to a financial issue at that time, I had to return home before submitting my work (I just tested its circuit at the laboratory and later I used its topology at home in some of my private projects).
Now, I wonder if, even in these days, the graduates in communications (around the world) are made to believe that a simple linear AM demodulator for any AM modulation index (unlike the known complex ones, as Costas Loop or using selective LC filters) doesn’t exist (not known yet).
Edited:
Sorry, being new here, I noticed now that I had better posting this thread in:
Forums > Electronics Categories > Radio and Communications
Recovering the modulating signal of a double sideband suppressed carrier signal is much harder than of a SSB-SC one.
But on the other hand, it sounded rather illogical, to me in the least, that receiving two sidebands (symmetrical) could be worse than receiving just one of them!
So, as an MS thesis, I designed and built (after many failures during about 5 months) a simple low-cost linear demodulator for DSB-SC.
Its mains components were:
1 LM339 comparator IC
1 CD4046 a PLL IC
1 CD4013 as flip-flop
1 CD4066 CMOS switches
Obviously, it works for any AM index; from m=0 (carrier with no modulation) to infinity (DSB-SC) while it has a frequency lock range (a PLL characteristic), as the AFC in FM receivers.
Also, being a synchronous AM demodulator, it is suitable for recovering hi-fi audio signals as well (as long the receiver bandwidth is wide enough).
And, if necessary, its components could be integrated in one low cost IC.
But, due to a financial issue at that time, I had to return home before submitting my work (I just tested its circuit at the laboratory and later I used its topology at home in some of my private projects).
Now, I wonder if, even in these days, the graduates in communications (around the world) are made to believe that a simple linear AM demodulator for any AM modulation index (unlike the known complex ones, as Costas Loop or using selective LC filters) doesn’t exist (not known yet).
Edited:
Sorry, being new here, I noticed now that I had better posting this thread in:
Forums > Electronics Categories > Radio and Communications
Last edited: