On 2/8/2012 6:38 PM, Jeff Liebermann wrote:
On Wed, 08 Feb 2012 15:41:08 -0800, Jeff
wrote:

Your 200ft of RG6a/u will drop the signal from
between 4dB at the low end, to about 6dB at the high end.

Some better numbers for RG6a/u:
Freq Atten
MHz -dB
10 0.8
50 1.4
100 2.9
200 4.3
400 6.4
1000 11.0

The CATV band is approximately 50 to 800MHz. With 200ft of cable, you
should see 2.8 to 16dB of loss. While there may be problem at the
high channels, all the lower channels should work.

Any idea where channel 428 would be in that frequency range?
That's a duplicate of 4,2 but in HD, and it works when 42 doesn't.

The 4 way splitter has a loss of about -7dB.

Just a point. I may not have made it clear. I had the tech put in two
2way splitters and connect me to the first one. Hoping to gain 3db.
(or 4) and it did make a difference.



Picking a random set top box:
http://www.zoran.com/IMG/pdf/Simplify_NextGen_STBs_Solutions.pdf
See Page 3. Sensitivity is -18dBm for 256QAM and -24dBm 64QAM.

At the low end, you have 0dBm in, 7dB loss in the splitter, 2.8dB loss
in the coax, resulting in -9.8dBm to the box. That's much more than
the -18dBm/-24dBm needed.

However, at the high end, things are not so wonderful. 0dbm in, 7dB
loss in the splitter, and 16dB loss in the coax, which delivers
-23dBm. That's 1dB of margin, which is not very good. Still, it
should work on the lower channels.

On 2/8/2012 7:01 PM, Joerg wrote:
amdx wrote:
Hi All,
I'm on a boat, about 170ft from the utility post.
Recently our cable company switched to the wonderful world of
Digital TV. I got the new digital converter and had no picture.
I took the box back and got a second box, still no picture. So now I
suspect a weak signal and confirm that it is the cable length. The cable
company came out and gave me a better cable than I had installed. At
this point I have a picture but it is intermittent. The signal at the
utility post has 3 outputs and had a four way splitter, I suggested the
cable guy put in two 2 way splitters and give me the stronger (first) tap.
That got my signal to work almost all the time. I'd like to get the
signal to work 100% of the time.


Looks like the cable guys screwed up.

a. They should be putting enough signal on that cable to overcome the loss.

b. They should be able to measure the amplitude of pilot signals at your
end of the cable and tell you how much above minimums they are.


I don't has access to electricity at the utility post, so an amp is
out. Although I could try an amp at the cable box end. Is that reasonable?
I would run two cables if there was a way to make it increase signal
strength.
Getting anymore from the cable company is not an option.
Any ideas to get a better signal?
Mikek


PS.

When the signal fails it seems channel 41 is ok and above 42 it breaks up.
Curious to know if there is an unusual frequency jump between those two
digital channels.



If all else fails you may need an amp. What Fred means with drop amp is
usually called a "mast preamplifier", like this:

http://www.amazon.com/Uhf-Vhf-Antenn...748729&sr=8-20

I don't know this particular one but essentially it should be
weather-proof. It gets its DC voltage via the coax, from a wall wart
that would plug in at your boat. So no need to run a power supply cable
up there.

Don't go for too much gain. This dreaded DTV falls apart rather easily
on the slightest distortion or cross-modulation. Not sure if the above
amp can handle that. You might need a more expensive one. Michael
Terrell might know which ones are good. What matters is dynamic range.

Also, make sure you have a perfect 75ohms match at your end. The cable
box from the cable company should provide that. if you have Internet
and/or phone through them as well check that connection so it doesn't
cause reflections. On a boat at sea stuff can corrode quickly.

Oh, and don't dare to watch that boobs channel while your wife's on the
boat :-)

Been trying to think of something funny to say about that...
Best I got is, she would say, "mine look better than those!

amdx wrote:
On 2/8/2012 6:38 PM, Jeff Liebermann wrote:
On Wed, 08 Feb 2012 15:41:08 -0800, Jeff
wrote:

Your 200ft of RG6a/u will drop the signal from
between 4dB at the low end, to about 6dB at the high end.

Some better numbers for RG6a/u:
Freq Atten
MHz -dB
10 0.8
50 1.4
100 2.9
200 4.3
400 6.4
1000 11.0

The CATV band is approximately 50 to 800MHz. With 200ft of cable, you
should see 2.8 to 16dB of loss. While there may be problem at the
high channels, all the lower channels should work.

Any idea where channel 428 would be in that frequency range?
That's a duplicate of 4,2 but in HD, and it works when 42 doesn't.


I believe that's entirely up to the cable company, you'd have to ask an
engineer there.

http://en.wikipedia.org/wiki/Digital_cable

Quote "For example, a cable company might call channel 5-1 "channel 732"
and channel 5-2 "channel 733"".


The 4 way splitter has a loss of about -7dB.

Just a point. I may not have made it clear. I had the tech put in two
2way splitters and connect me to the first one. Hoping to gain 3db.
(or 4) and it did make a difference.


Where does the other leg of that splitter go to? And is that end
properly terminated?

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

On Wed, 08 Feb 2012 19:24:06 -0600, amdx
wrote:

Now remember the problem is quite intermittent, but seems to be
happening almost daily for short periods.

Monitor the signal levels at the set top box and see if it coincides
with something nearby changing, such as the dock lights or operation
of heavy machinery. Maybe shove a DVM (digital voltmeter) into the AC
power and see if it moves around.

There should be no water in the cable, it's only a couple of months
old and both ends have crimp on connectors and are located in a box or boat.

I don't like crimp type connectors. Push on connectors are MUCH
better. Also, if the coax came from Radio Shack, all bets are off as
to the quality.

It does have diagnostics, I'm not sure if it is each channel though.
But I can get some info out of the box. I'll be there Friday and I'll
get that info and the model of the cable set top box.

Digital set top box diagnostics are different from analog. Instead of
per-channel levels, it might have levels for specific channels.

I'm using Comcast at the boat. We are lucky here (I think) in that
we have a choice of two cable companies.

If it's Comcast, you will probably still have the lower 72 channels
doing analog. Remove the set top box and plug in your TV directly.

Drivel is good.

The story of my life.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

Just a point. I may not have made it clear. I had the tech put in two
2way splitters and connect me to the first one. Hoping to gain 3db.
(or 4) and it did make a difference.

Where does the other leg of that splitter go to? And is that end
properly terminated?

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

right good question...OP, when you had the analog signal, was there
significant ghosting?

digital boxes might tolerate a WEAK signal but they are intolerant of
reflections.

Mark

amdx wrote:

On 2/8/2012 7:01 PM, Joerg wrote:
amdx wrote:
Hi All,
I'm on a boat, about 170ft from the utility post.
Recently our cable company switched to the wonderful world of
Digital TV. I got the new digital converter and had no picture.
I took the box back and got a second box, still no picture. So now I
suspect a weak signal and confirm that it is the cable length. The cable
company came out and gave me a better cable than I had installed. At
this point I have a picture but it is intermittent. The signal at the
utility post has 3 outputs and had a four way splitter, I suggested the
cable guy put in two 2 way splitters and give me the stronger (first) tap.
That got my signal to work almost all the time. I'd like to get the
signal to work 100% of the time.


Looks like the cable guys screwed up.

a. They should be putting enough signal on that cable to overcome the loss.

b. They should be able to measure the amplitude of pilot signals at your
end of the cable and tell you how much above minimums they are.


I don't has access to electricity at the utility post, so an amp is
out. Although I could try an amp at the cable box end. Is that reasonable?
I would run two cables if there was a way to make it increase signal
strength.
Getting anymore from the cable company is not an option.
Any ideas to get a better signal?
Mikek


PS.

When the signal fails it seems channel 41 is ok and above 42 it breaks up.
Curious to know if there is an unusual frequency jump between those two
digital channels.



If all else fails you may need an amp. What Fred means with drop amp is
usually called a "mast preamplifier", like this:

http://www.amazon.com/Uhf-Vhf-Antenn...748729&sr=8-20

I don't know this particular one but essentially it should be
weather-proof. It gets its DC voltage via the coax, from a wall wart
that would plug in at your boat. So no need to run a power supply cable
up there.

Don't go for too much gain. This dreaded DTV falls apart rather easily
on the slightest distortion or cross-modulation. Not sure if the above
amp can handle that. You might need a more expensive one. Michael
Terrell might know which ones are good. What matters is dynamic range.

Also, make sure you have a perfect 75ohms match at your end. The cable
box from the cable company should provide that. if you have Internet
and/or phone through them as well check that connection so it doesn't
cause reflections. On a boat at sea stuff can corrode quickly.

Oh, and don't dare to watch that boobs channel while your wife's on the
boat :-)

Been trying to think of something funny to say about that...
Best I got is, she would say, "mine look better than those!

And you know what you'd better reply!

Cheers

Phil Hobbs

On 2/8/12 7:27 PM, Sal wrote:
wrote in message
...
Hi All,
I'm on a boat, about 170ft from the utility post.
Recently our cable company switched to the wonderful world of
Digital TV.

snip

Getting anymore from the cable company is not an option.

I take respectful exception to that last sentence. My digital cable box is
about 130 cable-feet from the pole. My signal is tapped enroute for digital
telephone, tapped enroute for Internet and then split (by me) so I can feed
analog signals via a disttribution amp serving bedrooms, kitchen and shack.
I get enough from the pole tap to do the job.

I respectfully agree! 8^)

I don't know exactly how it's done now, but when I worked in the Cable
industry many moons ago, we had a lot of adjustment we could make. Even
more, we had variable by frequency attenuators so we could ensure that a
flat signal showed up. There was a lot of signal at the amplifiers, and
if we really needed more oomph, we could put in a distribution amp.
Another amp was really rare.

Somebody is treating you badly -- maybe the cable company, maybe the marina.
Yes, the approach for you to buy and install an inline, remote-power amp at
the pole is entirely valid, technically. However, that's not in keeping
with reasonable expectations. You needn't roll over so easily. It's
supposed to work.

What -- Are you worried you might offend somebody? That "somebody" seems
quite okay with kicking you in the ankle. Or elsewhere.

Yeah, there is something wrong there. For as much as people hate
Comcast, when I had cable internet put in, they replaced all the cable
from the pole to the house, and a lot inside the house. I did talk them
out of replacing the new cable I had put in, but insisted on putting new
connectors on them. The measured all the levels and set them high enough
that I'd be able to add more televisions if I liked.


Time to call the cable company and tell them you want your MTV.


- 73 de Mike N3LI -

On Wed, 8 Feb 2012 18:21:19 -0800 (PST), Mark wrote:



Just a point. I may not have made it clear. I had the tech put in two
2way splitters and connect me to the first one. Hoping to gain 3db.
(or 4) and it did make a difference.

Where does the other leg of that splitter go to? And is that end
properly terminated?



Cable installers terminating things? You must be ****ing joking.
They would have to have an IQ above 25 for that.

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

right good question...OP, when you had the analog signal, was there
significant ghosting?

digital boxes might tolerate a WEAK signal but they are intolerant of
reflections.

Why would there be a reflection in a closed cable run?

On Wed, 08 Feb 2012 18:52:10 -0800, The_Giant_Rat_of_Sumatra
wrote:

On Wed, 8 Feb 2012 18:21:19 -0800 (PST), Mark wrote:



Just a point. I may not have made it clear. I had the tech put in two
2way splitters and connect me to the first one. Hoping to gain 3db.
(or 4) and it did make a difference.

Where does the other leg of that splitter go to? And is that end
properly terminated?



Cable installers terminating things? You must be ****ing joking.
They would have to have an IQ above 25 for that.

*WAY* above your pay grade.

On Wed, 08 Feb 2012 19:30:07 -0600, amdx
wrote:

Any idea where channel 428 would be in that frequency range?
That's a duplicate of 4,2 but in HD, and it works when 42 doesn't.

Ummm... it's ugly. There are up to 10 standard definition or 2 HD
channels crammed into a 6 MHz wide RF slot. In order to untangle
this, you would need to run a PSIP decoder and extract the CVCT
record:
http://en.wikipedia.org/wiki/PSIP
to figure out where digital CH 428 fits. It could literally be
anywhere. However, if you happen to have an tuneable notch filter
(which I happen to have), you can stuff it in series with the cable,
and spin the dial until the signal disappears. Then, just read the
dial. (Comcast seems to be putting well paying and popular channels
on the lower frequencies, and obscure junk on the higher frequencies.
I'm not sure if this is intentional, accidental, or my imagination).

The 4 way splitter has a loss of about -7dB.

Just a point. I may not have made it clear. I had the tech put in two
2way splitters and connect me to the first one. Hoping to gain 3db.
(or 4) and it did make a difference.

Yeah, I saw that. I guess I wasn't too clear. The input signal can
vary over a 10-16dB range, and it still should work. The 3dB
difference between a two port and a 4 port splitter isn't going to
make much difference, exept at the higher channels.



--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS