Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site nic_vax.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!decvax!mcnc!philabs!cmcl2!seismo!uwvax!astroatc!nic_vax!brown
From: brown@nic_vax.UUCP
Newsgroups: net.consumers
Subject: Re: Re: CableVision of Central Florida: the scoop
Message-ID: <145@nic_vax.UUCP>
Date: Fri, 3-May-85 21:12:14 EDT
Article-I.D.: nic_vax.145
Posted: Fri May  3 21:12:14 1985
Date-Received: Mon, 6-May-85 00:03:40 EDT
References: <138@nic_vax.UUCP> <1651@bmcg.UUCP>
Distribution: net
Organization: Nicolet Instrument Corp. Madison WI
Lines: 41

> > *** REPLACE THIS LINE WITH YOUR MESSAGE ***  OK, I will!!!
> > 
> > As I said in my followup on Saturday, I called CableVision of Central Florida.
> > Here is the scoop from there engineer.
> > 
> > As I had suspected, HBO is a trap type pay channel.  If you don't pay for it,
> > they trap out the carrier, so that all you are left with is the high end of
> > the video, all of the color information and the sound carrier.
> > 
> I'm not to sure what you mean by a trap, but if they supply the video info
> and more important the sound, won't a sipmle and cheap to build sync
> generator give the signal full video. Drop the sync into the blanking
> sector and off you go.

Sorry, I should have said what a 'trap type pay channel' is.

There are two kinds of trap systems.  The first type, the same used in the
above Florida system, is where the signal is sent down the system like any
other channel.  If you don't get the pay channel, they filter (trap) out the
video carrier.  Without the main carrier, the tv doesn't have much left to
go on.  The second type of trap is where an extra carrier is added to the
signal.  Around here, before they stopped doing it, another carrier, equal
in amplitude to the main carrier is added 2.25 MHz above the main carrier.
This causes the tv agc to run the rest of the signal into the noise.  Too
much signal, so the gain is changed.  This type of system doesn't even allow
you to hear the channel either.  But, it is a bad idea because to get the
pay channel, that added carrier is filtered (trapped) out.  It also filters
out part of the high frequency picture information.  The sharp edges aren't
sharp anymore.

I believe the thing you described above is called 'gated sync'.   That idea
is used in another cable system next to Madison.

-- 
              |------------|
              | |-------| o|    JVC HRD725U 
Mr. Video     | |       | o|  |--------------|
              | |       |  |  | |----| o o o |
              | |-------| O|  |--------------|
              |------------|     VHS Hi-Fi (the only way to go)
   (!ihnp4!uwvax!astroatc!nic_vax!brown)