On Mon, 25 Apr 2005 23:45:15 -0400, Jerry Avins <jya@ieee.org> wrote:> Is it mitigating that I last dealt with this in 1954?When, as a three year old, I was playing on the work bench my father built me for my third birthday. Gotta love the depth in this newsgroup. To the OP: aren't conventional modern TV transmitters built as a DSB modulator passed through a (high-pass) filter added to a separate carrier (and to a separate sound carrier)? Would this architecture be useful to you? Good fortune, Chris Hornbeck "This has been an account for those who don't keep them" J-LG, _Tout Va Bien_ 1972
Hilbert Vs bandpass filter in VSB Modulation
Started by ●April 24, 2005
Reply by ●April 26, 20052005-04-26
Reply by ●April 27, 20052005-04-27
Mark wrote:>I don't understand your question. Baseband video is a real signal from >DC to about 4.2 MHz. When applied to a DSB AM modulator, it creates >symmetrical sidebands. Filtering removes part of the lower sideband >(at RF, at IF the upper sideband is removed). Alternatively the >phasing method can be used to remove part of the unwanted (vestigial) >sideband. > > >Its easy for a SAW designer to design the required SAW filter difficult >for me :-) ) >I think the process is similar to designing an FIR filter. > >The first part is the same. When you get to the "allowing for quantisation effects" stage with an FIR, you replace that with an "allowing for diffraction and other nasties at the ends of the fingers" stage.>There is a large selection of IF and also Ch 3 and Ch 4 SAWs >commercially available for low cost modulators. There are also high >quality expensive ones. >What is your application? Is it a low cost consumer device for >connection to a single TV or a high quality CATV or broadcast device? > >Regards, Steve
Reply by ●April 27, 20052005-04-27
"What is your application? Is it a low cost consumer device for connection to a single TV or a high quality CATV or broadcast device?" -- high quality CATV or broadcast device
Reply by ●April 27, 20052005-04-27
Chris Hornbeck wrote:> On Mon, 25 Apr 2005 23:45:15 -0400, Jerry Avins <jya@ieee.org> wrote: > > >>Is it mitigating that I last dealt with this in 1954? > > > When, as a three year old, I was playing on the work bench > my father built me for my third birthday. Gotta love the depth in > this newsgroup. > > To the OP: aren't conventional modern TV transmitters built > as a DSB modulator passed through a (high-pass) filter added > to a separate carrier (and to a separate sound carrier)? > > Would this architecture be useful to you? > > Good fortune, > > Chris Hornbeck > "This has been an account for those who don't keep them" > J-LG, _Tout Va Bien_ 1972The sound carrier is usually part of the video signal that is modulated. Sound is usually recovered after the video detector with an FM detector set at 4.5 MHz. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●April 27, 20052005-04-27
this is true for most small consumer grade modulators CATV often uses separate modulators but shared amplifier stages broadcast TV typically uses separate transmitters and the RFs are diplexed to the antenna feed with lots of big plumbing
Reply by ●April 28, 20052005-04-28
On Wed, 27 Apr 2005 11:12:20 -0400, Jerry Avins <jya@ieee.org> wrote:>The sound carrier is usually part of the video signal that is modulated. >Sound is usually recovered after the video detector with an FM detector >set at 4.5 MHz.Perhaps I'm mis-communicating. Broadcast transmitters have always (?) used separate pix and sound RF amplifiers. Perhaps you mean the chroma subcarrier ? Anyway, all I'd meant to suggest was the suppressed-carrier DSB with following filter model for the OP's purpose. Dunno, might be useful. Chris Hornbeck "Don't panic."
Reply by ●April 28, 20052005-04-28
Chris Hornbeck wrote:> On Wed, 27 Apr 2005 11:12:20 -0400, Jerry Avins <jya@ieee.org> wrote: > > >>The sound carrier is usually part of the video signal that is modulated. >>Sound is usually recovered after the video detector with an FM detector >>set at 4.5 MHz. > > > Perhaps I'm mis-communicating. Broadcast transmitters have always (?) > used separate pix and sound RF amplifiers. Perhaps you mean the chroma > subcarrier ? > > Anyway, all I'd meant to suggest was the suppressed-carrier DSB with > following filter model for the OP's purpose. Dunno, might be useful.I'm the miscommunicator. Sound and video carriers are amplified separately to relax the video final's bandwidth requirements. The composite signal is treated as a whole by the receiver, and instead of pulling the audio carrier separately from the IF, it is taken from the output of the video detector. this "intercarrier sound" method avoids problems that might arise from mistuning the IF. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
