See if you can find a National Linear Applications Handbook--1986, look
at AN-402. It discusses the LM1889 and LM2889 chips. The VSB Filter is a
Vestigial Sideband Filter and is a pre-packaged circuit cut to channel 3
and 4. You have the channel 3 and 4 Video Carriers (AM) and the channel
3 & 4 Audio carriers (FM) 4.5 Mhz removed from the AM video carrier, and
then the Chroma signal at 3.58 Mhz these frequencies are closely linked
for a 6Mhz wide bandwidth for channel 3 or 4. The sound and Video
oscillators use lc components, the SAW (VSG) filter is premanufactured
you could probably design a LC band pass filter to limit the Vestigial
side band. A TV channel has a lopsided picture bandwidth. It is 4.5 Mhz
on the upper side band and 1.25 Mhz on the lower side band. The
vestigial filter cuts off the lower 3 Mhz of the lower side band tho
keep the video carrier from channel 3 from interfering with the audio
and video carriers of channel 2.

I dont have the document in pdf form or would send it, maybe someone
else has it...

Vern Jones

Herbert Graf wrote:
>
> Was wondering if anybody one the list could help me with this one.  I
> recently purchased an RF modulator from www.bgmicro.com to convert composite
> video to ch2 which uses the LM1889. I am having trouble in two ares.
>
> First the data I have says that I have to feed in a "chroma carrier", what
> the heck is that? Is that just a 3.79... MHz signal? Any idea on what kind
> of amplitude would do?
>
> Second the module only has ch3 and ch4 as choices, I would like to convert
> it to ch2 operation, I think I know how to modify the oscillator section but
> there is a section in the module labeled "ch3 VSB", I assum this is tuned
> for the Ch3 frequency and that I would have to change this circuitry as well
> to get it to work?
>
> Basically I'm looking for anyone who's worked with this chip, and anybody
> who has a datasheet (national no longer has the datasheet). Thanks for any
> assistance. TTYL
>
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