Increasing Cable TV signal strength

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. 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.

Reply to
amdx
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In message , amdx writes

Despite your long 170ft drop cable, were you getting good analogue signals before the change to digital? If so, it could be that something is not right. Normally, even if you have had only fairly mediocre analogues, the digitals are good.

Otherwise.... It sounds like your signals are just too weak. As things are, and if you can, the obvious fix would be to overcome the substantial loss of the

170ft drop cable by fitting an amplifier at or near the utility post (not at your end), and power it with low voltage via the coax from your end (ie similar to a line-powered masthead antenna amplifier). However, you would need to consult with the cable company to see if they were OK with letting you do this. It could be that they might be able advise you on the most suitable amplifier to use. It's not rocket science, but you have to be a little careful not to break any of their rules and generally do anything they don't approve of.
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Ian
Reply to
Ian Jackson

That's about 10dB loss at midband for RG6.

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That was just a 3dB boost.

s
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Really? There are such things a power inserters and compatible drop amps that allow you to power the amplifier over the cable from the user end. For RG6 18ga stranded that is about 0.6V loss at 250mA and therefore doable,

Forget it.

Use a 15dB gain drop amp with power inserter, but that's just a guess. Would help if you actually knew signal levels like what the receiver requires for optimum reception and what the cable co sources. Putting the amplifier at source gives you a typical system noise figure of

3dB, but putting it at your end limits your NF to 10dB minimum from the start.
Reply to
Fred Bloggs

Adding an amp at the cable box isn't all that likely to work... you can try it, but don't get your hopes up. Unless the amp has a significantly lower "noise figure" than the RF front end in the cable box, all you'll be doing is adding noise... the desired signal will be stronger, but the noise will be stronger yet.

Something you could do, is add a single-port RF amplifier right at the utility post splitter, where your tap comes off of the feed. You can buy amplifiers of this sort which are designed to receive "phantom power" through the coax cable... you'd install a "power injector" at your boat, which feeds a DC voltage up the coax to the amplifier. This is probably your best bet:

- It would amplify the signal before it's attenuated by the 170-foot cable run.

- It won't require a power supply at the post... just at your boat, where you already have power.

- It shouldn't interfere with the other taps on the splitter, even when the amplifier is not receiving power from your boat.

You'd be looking for an "antenna mast" type of preamplifier. The Channel Master 0068DSB or 7777, Winegard AP-8700 or AP-8275 or HDP-269, AntennaCraft 10G212, or one of the Blonder Tongue Galaxy III models might do the job for you. You'll probably want a "75 ohm in,

75 ohm out" model, which would connect directly to the 75-ohm coax.
--
Dave Platt                                    AE6EO
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Reply to
Dave Platt

.
s
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s up.

see URL:

41 is 324 - 330MHz and 42 is 330-336 MHz cables attenuate more at higher frequency.

By ALL means, if you're going to add an amplifier, add it at the source location, not at the receiver location Cheap, but good, ones are available from microcircuits. Can you buy a line driver from your CATV company?

I suspect the 'better' cable is only marginally better. What is the EXACT cable you're using? what is its attenuation per foot per MHz? You can buy extremely low loss coax, but you may have to send in your first born. Go to a local NRTL [EMC Test Lab] and see if they can (are willing to) order a length for you.

Find the highest channel you wish to receive and the frequency associated with that. Now you can balance the amplifier gain with the cable loss to determine if it will work. Note you already know that

170 ft of ?? cable gets you up to channel 41, so from that number you can estimate just how much drop your receiver can take before it stops receiving.
Reply to
Robert Macy

Are you sure it's a signal strength problem? The cable guy should have been able to measure the signal at your cable box. Are the people using the other taps having problems? If you're on a boat, you might be at the end of the cable run. In that case, you might be able to get them to crank up the gain in their distribution amp. Power at the pole is not a problem. You can get amps that are powered through the signal cable to your cable box. Getting them to let you install it is another matter. You can get MUCH better wire, for a price.

Signal strength is not the only problem with digital TV. Reflections in the system can confuse the decoder. Are there any unterminated cables on the other taps?

I have OTA antenna digital TV. Plenty of signal, but reflections cause significant drop outs on some channels. More signal won't fix that. In fact, I have a variable attenuator to REDUCE signal strength. I tweak the signal level for fewest dropouts.

Might be electrical noise coupled in thru the ground system.

Bottom line is that you pay the cable company for TV reception. It's their responsibility to provide you with a watchable signal. You shouldn't have to tell them what to do. They should just FIX it!!

Reply to
mike

You are quite correct. However, digital is generally capable of working to lower signal levels than analogue. It's amazing how rubbishy digital signals can be, yet still give perfect pictures - but don't expect miracles!

I see that several others have also suggested a coax-powered amplifier. [If the cable company can't give you more signal level, it's the only solution.] As suggested, they should be able to provide a suitable amplifier and power unit - or at least advise you what to use.

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Ian
Reply to
Ian Jackson

The cable company probably has amplifiers that can be powered over the cable run. If not, those amps can be found on ebay. Be sure to get a bidirectional amplifier because some systems send the control signals back up the cable to the cable company (Comcast in the southeastern US, for example.)

John

Reply to
news

At only 170 feet, that should not be a problem. My cable runs down a utility post, then over 200 feet to my house. It goes to a 2 way spitter and then about 30 feet to a cable modem. The other end goes to anotehr two way splitter, one side to a regular TV and the other to a digital box.

No problem with the TV signal at my house, and the internet is around 7 MB or however they measuer it. That is by my test on the internet and what they say I am paying for in the speed./

Sounds like they need to send more signal from the main cable to the taps to your line.

Reply to
Ralph Mowery

Ok, 200ft of coax. Presumably RG6a/u.

You have been assimilated. Resistance is futile.

Something is wrong. The nominal signal from the cable drop is suppose to be 0dBm. If there's a splitter involved, they like to crank it up to about 10dBm. Your 200ft of RG6a/u will drop the signal from between 4dB at the low end, to about 6dB at the high end. Your set top box is suppose to operate with a 10dB margin. If you would kindly disclose the maker and model, it might be possible to find the specs. Typically, you'll have at least 10dB margin. Even with 200ft of coax, you should have 4 to 6dB margin.

Drag your cable box and TV over to the splitter and try it on the incoming drop. If that works, move to the ports on the splitter. Make sure that the unused ports are terminated properly. If that doesn't work, call your unfriendly cable company and ask them why they don't have sufficient level to operate your set top box without the 200ft cable. If it does work, find a 200ft RG6a/u cable that isn't saturated with water. Try to get some compressing fittings instead of the crappy crimp type.

Your unspecified cable set top box may also have some user accessible diagnostics which include per channel signal levels. You may want to check those.

I'm not familiar with Knology, but I suspect they do the same thing as Comcast. With Comcast, the lower 72 channels are still analog in my area. If so, you can probably plug your TV directly into the cable, set the TV for cable frequencies, not broadcast, and see if that still plays.

Hint: Troubleshoot by substitution.

Drivel: I spent about an hour troubleshooting my TV distribution system, only to find a brand new Type F "barrel" connector, with no center connections. That which is most obviously correct, beyond any need of checking, is usually the problem.

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
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Reply to
Jeff Liebermann

< snip >

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.

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.

"Sal"

Reply to
Sal

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.

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

Picking a random set top box:

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.

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
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Reply to
Jeff Liebermann

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

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.

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.

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

Drivel is good.

Reply to
amdx

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.

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.
Reply to
amdx

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

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

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

[...]
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Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

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.

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.

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

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.

The story of my life.

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
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Reply to
Jeff Liebermann

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

Reply to
Mark

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.

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 -

Reply to
Michael Coslo

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:

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).

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.

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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
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Reply to
Jeff Liebermann
< snip >

No way to know from here, but they may not be able to add another amp.

While I was looking for something else, I lurched into this page:

While its intended audience is Internet modem designers, the noise discussions are informative with regard to other signals, too.

My point: When you try stringing too many amps in line, the signal-to-noise ratio (SNR) eventually becomes unacceptable. (Remember the acceptable SNRs cited for 256 QAM and 64 QAM.)

"Sal"

Reply to
Sal

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