From: Robert Macy on
On Dec 5, 2:59 pm, Jeff Liebermann <je...(a)cruzio.com> wrote:
....snip...
> Ok, the coax is suspect.  This is easier to troubleshoot by
> substitution.  Find a 50ft piece of decent 75 ohm coax cable.  Run it
> in place of the suspected 33ft piece.  If it magically fixes the
> problem, your old coax is history.
....snip...
> >Everything was fine until the digital conversion, and now this tv that
> >I watch a lot shows a grainy picture.   All the other tvs have great
> >pictures, and even for this one, when I supply a signal directly from
> >a set-top digital converter box, only 3 feet of cable, it shows a
> >perfect picture**.
>
> I guess "grainy" means you're getting a weak signal.  Well, drag one
> of your other TV's over to this location and see if it's a consistent
> problem.  If the 2nd TV is also "grainy", then you probably have a low
> signal level for some reason.  Again, it can be the cable or the
> connectors.  A broken shield connection will still deliver a signal,
> but at somewhat lower level.  Also, substitute the coax with a known
> good one as I previously suggested.
>
....snip...
> Jeff Liebermann     je...(a)cruzio.com
> 150 Felker St #D    http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann     AE6KS    831-336-2558

Sorry, for jumping in here in the way of Jeff's capable hands, but
agree with honing in on potential bad connections in that old coax.
Plus, the description of the received signal reminds me of when I had
to use an amplifier to overcome the loss from attempting to use a
splitter, only to find that some strong station was doing?? whatever
to create an overlay image on top of my viewing. Since the crystals
are so close, frame images drift over the top of each other. Looks
like the overlay dot patterns like OP described. For me, was
confirmed when one day I could actually read the call letters of the
'offending' overlay.

Also, OP said this started happening when DTV took over. That day a
lot of broadcast stations started switching their power signals
around. Even as late as October 31, they were still being shifted.
Perhaps, the band change showed up mixing, or affecting the AGC

Background of my experience with this: I added a security camera to
our home viewing. Simply popping to unused channel and I could see
who was at the front door. Sadly, I learned that RF Modulators
produce such a weak signal that I had to add an amplifier to make up
for a single one to four splitter stage. And then the problem of the
dynamic range of antenna reception reared its ugly head. And mixing
in the amp, and ad nauseum.
From: Joe Rooney on

"mm" <NOPSAMmm2005(a)bigfoot.com> wrote in message
news:tollh51ecqf64sh25unhdbsuilbns30l9n(a)4ax.com...
> On Sat, 5 Dec 2009 15:52:16 -0600, "David" <someone(a)somewhere.com>
> wrote:

snip

> dark colored lines.
>
> The end result is a picture that's pretty good, by 1970's over-the-air
> standards, and the darks are darker now than they were in June, but
> it's not smooth. I can live with this of course, for years if it
> works out that way, but I like to fix things.
>
>
>
> >David

Keep in mind a 3 way splitter has two 3.5db and one 7 db out.

Joe Rooney



From: mm on
On Sun, 6 Dec 2009 00:24:47 -0800, "Joe Rooney"
<ikerooneyat(a)bigvalley.net> wrote:

>
>"mm" <NOPSAMmm2005(a)bigfoot.com> wrote in message
>news:tollh51ecqf64sh25unhdbsuilbns30l9n(a)4ax.com...
>> On Sat, 5 Dec 2009 15:52:16 -0600, "David" <someone(a)somewhere.com>
>> wrote:
>
>snip
>
>> dark colored lines.
>>
>> The end result is a picture that's pretty good, by 1970's over-the-air
>> standards, and the darks are darker now than they were in June, but
>> it's not smooth. I can live with this of course, for years if it
>> works out that way, but I like to fix things.
>>
>>
>>
>> >David
>
>Keep in mind a 3 way splitter has two 3.5db and one 7 db out.

Aha. That would certainly account for a difference! I'll check
later today. In fact, I'll take out the splitter and connect just
the one giving me trouble.

Thanks a lot.
>
>Joe Rooney
>
>

From: Jeff Liebermann on
On Sun, 06 Dec 2009 12:03:52 -0500, mm <NOPSAMmm2005(a)bigfoot.com>
wrote:

>On Sun, 6 Dec 2009 00:24:47 -0800, "Joe Rooney"
><ikerooneyat(a)bigvalley.net> wrote:

>>Keep in mind a 3 way splitter has two 3.5db and one 7 db out.

Wrong. A splitter reduces the output by -3dB which is half the power.
The extra -0.5dB loss is from losses in the bifilar wound xformer. If
two of the ports each have half the input power, there's nothing in
the budget left for the 3rd port.

Googling for a typical 3 way splitter:
<http://www.twacomm.com/catalog/model_CT413.htm?sid=1F79205DEA0D1B9FF1BF82ACDC4C33D2>
I find 2 ports with -6.5dB loss and one port with -3.5dB, which makes
more sense. (Actually, it should be -7.0dB loss).

A 3 port looks like a tree. It starts with a two port splitter, where
one output is brought out for -3.5dB loss. The other port goes to yet
another splitter, with again divides the output in half, for -7dB from
each of the two ports.

>Aha. That would certainly account for a difference! I'll check
>later today. In fact, I'll take out the splitter and connect just
>the one giving me trouble.

Except that you said you're using 2 and 4 way splitters, which are far
more common than a 3 way.

--
Jeff Liebermann jeffl(a)cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
From: Jeff Liebermann on
On Sat, 5 Dec 2009 20:30:48 -0800 (PST), Robert Macy
<macy(a)california.com> wrote:

>Sorry, for jumping in here in the way of Jeff's capable hands,

Grumble...

>but
>agree with honing in on potential bad connections in that old coax.

There's a fairly easy way to detect bad connections. These invariably
result in coax leakage, where the coax cable magically becomes an
antenna. Find a portable TV receiver, tune it to CATV channels not
OTA (over the air) channels, and sniff around with the portable
antenna looking for leaks (actually called "ingress"). This is
roughly what the CATV people do along the distribution cables using a
pilot carrier. A broken shield, broken connector, and possbibly a
missing termination, should all show up as excessive leakage.

Personally, I prefer visual inspection, a TDR (time domain
reflectometer), signal level measurements, or just a pre-emptive
replacement.

--
Jeff Liebermann jeffl(a)cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558