OT: just for those intersted about analog tape

[Bill Vermillion]

On or about Mon, Jan 10 10:07 , while attempting a Zarathustra 
emulation Bill Akers thus spake: 

> Bill Vermillion wrote:
> 
> >On Fri, Jan 07, 2005 at 11:25 , Bill Akers gie sprachen "Vyizdur 
> >zomen emororz izaziz zander isorziz", and continued with:

> >>Bill Vermillion wrote:

> >>>If you got the wrong sync pulse the picture would slip down 1/2
> >>>frame. 

> >>What??? Please explain what this does!!! My experience says it
> >>would just lose a part of one frame and all subsequent frames
> >>would be right back in proper order.

> >I'm pulling this from memory of about 35-40 years ago.  

> >I'm trying to remember if I saw the guy editing the tape
> >at KXLY-TV in Spokane Wash, of WFTV in Orlando.  If it was
> >the former that was in 1962 and the machine was an RCA VTR-1 [or
> >something close to that].   That was a CBS station and I thought it
> >was strange as the local NBC station also had an RCA and I'd have
> >thought with the competition they would go with Ampex.

> >Three 6 foot tall racks.   I left Spokane for Orlando
> >in August of 1962 - so forgive me if my memory has rusted like the
> >tape.

> >It's been so long since I've been near one of those beasts you
> >could be right.  I didn't do the editing but was wathching someone
> >else.  That was in the days when all TV had vertical hold and
> >horizontal hold knobs on the front too.

> The reason for the knobs was to compensate for warming up
> and aging of vacuum tubes and other components. Over time
> the inter-electrode capitance of the vacuum tube, or the
> capacitive or indusctive values of circuit components, would
> change slightly to a lot causing the vertical or horizontal
> oscillator's frequency to shift enough that it could no longer
> be synced by the sync signals that were part of the video
> stream from the station. The hold knobs were used to compensate
> properly for this phenomenon.

The first to go was horizontal sync, and later vertical.  Thank
goodness for phase locked loops that came later.

> I can understand if the station wanted to be precise enough to
> prevent the customer's television from 'flickering' during a
> show, but how did they prevent it from happening when switching
> from a show to a commercial for instance?

There is normally a master sync generator that all are slaved to.

It's been a long time, but when I took my FCC First Class license
test it was primarily tube technology.  Transistors weren't thought
to be reliable enough.  And I remember the heaters we had to use
on our crystals to keep the transmitter on frequency.

+/- 20 cycles/second - on things that ran from about .5MHz to 1.6Mhz.

That's a tolerance of 1/50000th of a second.  And today we
are meausuring speeds in home computers in billionths and
trillionths of a second.  [And even smaller in high tech arenas].

Boy have things changed.   It's almost like magic.

Bill

-- 
Bill Vermillion - bv @ wjv . com