Re: best way to get a //c monitor cable?

[mjmahon@aol.com (Michael J. Mahon)]

Kevin wrote:

>Last
>night I set up the 1084s next to my Apple //c system and plugged the
>beast in.   The picture was perfect.   I must say the //c has great
>composite output.   One thing I noticed after juggling the computer
>around was no picture!!!  So I gently pulled the cable out slightly
>and the pic appeared? Gave me a scare!!   It seems if I push the cable
>into the rca jack (on the //c) all the way- there is no pic but if it
>is not pushed tight the picture is crystal clear (in both mono and
>color).  Is this normal?   

It is if the RCA connector in the //c is worn (loose) as many are.

This is the actual cause of almost all faulty video on Apple IIs
when they are used with a monitor (not a modulator and a TV).

Apple II video is a low impedance signal of about 1.5v amplitude.
All monitor RCA inputs are essentially bandwidth limited at less
than 25MHz.  As a result, any visible "interference" is not the
result of pickup in the cable, but imperfect contact on either
or both of the signal lead and the shield lead of the RCA
cable--often not the cable itself, but the RCA connector on
the computer main board.

There are certainly defective RCA cables--intermittent shorts
and opens are most common--but you could use a 3ft length
of twisted pair to connect Apple II video to a monitor and you
would never be able to tell the difference.

A controlled experiment would consist of having someone
else randomly (as in tossing a coin) connect one or the other
monitor cable while you record whether you think the picture
is better or worse.

Unless the cable is truly defective, or longer than 4ft-5ft,
you won't be able to see a _real_ difference.

The U.S. particularly seems to have the misconception that
many subtle problems are corrected by using cables whose
primary distinction is that they are priced at 10x-30x their
cost.  These folks may also notice that placing a flourite
crystal oriented _precisely_ north/south on top of their
monitor or speakers  really clears things up.  ;-)

The only relevant properties of a video cable for an Apple II
are that it 1) make good contact at both ends, 2) be secure
enough mechanically for its environment, and 3) not have
excessive shunt capacitance (usually OK if short).  If you
are operating a TV set or shortwave radio nearby, then you
may need a couple of loops through a ferrite bead inside the
(shielded) case, and the outer shielding should be of better
quality, but that's only to prevent excessive _radiation_, since
any signal _absorption_ (as from a nearby radio station) will
be too low level to be visible on a monitor (unless you are
_next door_ to a radio station  ;-)..

-michael

Check out parallel computing for 8-bit Apples on my
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