View Single Post
Old 25th Feb 2005, 1:14 pm   #14
David_Robinson
Pentode
 
David_Robinson's Avatar
 
Join Date: Feb 2004
Location: Nottingham, UK
Posts: 94
Default Re: Multi-Channel VHF Modulator Design

Quote:
Originally Posted by Duke_Nukem
Just a basic cross hatch perhaps ?
Great idea. Any volunteers?
Quote:
Originally Posted by oldeurope
look what I have found.
Interesting. You would need two of them to do vision and sound, and you would have to get the I2C data into the chips from the PIC.

Regarding your concerns about modulation depth, the Freescale data sheet quotes 93% typical which sounds pretty good. I decided to find out what this looked like in the real world. The attached photo shows the output from the vision detector on a typical TV (actually a Thorn 980 series). I have set the second trace to show where ground is. Of course the voltage drop in the detector diode (germanium in this case) increases the apparent modulation depth. I think this is known in technical terms as "near enough".

By the way the sound modulator in my design is programmed to negative vision modulation mode and will actually give 100% mod.
Attached Thumbnails
Click image for larger version

Name:	Vision demod.JPG
Views:	270
Size:	81.7 KB
ID:	264  
__________________
Look that up in your Funk and Wagnall's

Last edited by Dave Moll; 27th Jun 2007 at 9:22 pm. Reason: correct for username change in quote
David_Robinson is offline