Question: Occasionally blinky reception; Damaged cable (pic incl.) contributing?

U

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Guest
#1
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Every few minutes our TV has pieces of the picture appear wrong/sound sputters and sometimes this is also followed by a second or two of blue screen. This happens on a number of channels, not all, and channels affected/frequency of issue, does vary with the direction of the antenna (8 element VHF-only Yagi currently sitting atop our metal framed patio table with plastic fFrisbees keeping the longer elements away from the tables frame) and time of day.

I therefore believe that the antenna is not faulty, but that the signal strength is occasionally dropping below the TV's tuner threshold because the antenna is not high enough gain, or there is a drop in signal strength between the transmitter and the TV possibly caused by the damage in the cable and not just that I haven't put the antenna back on the roof/there isn't enough signal strength at my house for my small antenna to pickup enough of it. So, if no-one disagrees with that assessment, questions, please:

1) What is your impression of the damage pictured? How likely is it that it is affecting the impedance of the cable?

2) As I am unemployed currently, is there an inexpensive way to test the cable's impedance to make sure the damage is just superfical, and can therefore just have electrical tape applied for watertightness.

3) As I have never seen a VHF/UHF signal strength meter like the ones for Satellite reception (Is this because it is easier to simply measure signal strength of a wide band when it is in the Ghz ranges?), would anyone suggest using a TV card for signal strength monitoring? I don't currently have one of these, and haven't yet seen one that has drivers&software for Linux, so if use of such a card is an idea, does anyone has any suggestions for inexpensive/¿free? options?

Thanks!
Morrie
 
#3
The simplest test you can do on coax is just a basic check for continuity, and shorts using an ohm meter, or low voltage continuity tester.
You can not test ohms impedance with an ohm meter. You are only testing continuity and shorts. I encourage every one to test all coax runs for basic continuity, and shorts. You can not do such tests with the coax hooked up to anything. Some baluns and antennas will test as direct short at DC.
https://www.youtube.com/watch?v=9AE9F-TLIjk
Etekcity Digital Multimeter (DMM) Multi Tester Voltmeter Ammeter Ohmmeter - AC / DC Voltage, DC Current, Resistance, Continuity, Diodes, hFE Tester with Backlit LCD - - Amazon.com
http://www.amazon.com/Sperry-Instru...1_3?ie=UTF8&qid=1434744177&sr=8-3&keywords=co
Some televisions and converter boxes have very useful signal quality meters. I've seen others that are worthless. I will address the meter question a bit more when I have more time to chase down some links. Yes I've seen some reference to some low cost broadband SDRs that might be of use. I'll chase that down when I have more time.
Steve
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#4
Morrie,

As Steve mentioned, some TVs and Converter Boxes have useful signal quality meters but please understand they are not signal strength meters. A very low signal strength with a high-quality will rate number approaching 100 -- but -- a low-quality high signal strength will rate with much lower numbers and your tuner may not be able to decipher a poor quality (confused) signal.

Antenna height is usually the key to good reception but (example) 20 feet above ground level may not be as good a location for your antenna whereas 18 feet or 22 feet might be ideal.

The damaged area of the coax may be acting as an antenna, allowing signals to enter or exit the coax and it certainly is not waterproof: water entry will kill your reception so your damaged coaxial cable should be repaired or replaced with new RG-6. If you are certain there has been no water entry, you could cut out the damaged areas, install new 'F' fittings and use a 'double-female' connector to complete the job: the cost would be minimal. Radio Shack, Fry's, even Lowes has those fittings.

Next, your metal framed patio table is likely having an unpredictable effect on your antenna. TV antennas should be located at least 3 feet away from any metallic object and as far away from metal roofs, metal siding and metal gutters as reasonably possible.

If you are interested in other recommendations, please post the URL result of your free antenna survey for us to study. Be sure to include the maximum possible height above ground level where you could install your antenna and use your actual address: that site will automatically conceal your address for your security. TV Fool

Jim
 
U

Unregistered

Guest
#5
The simplest test you can do on coax is just a basic check for continuity, and shorts using an ohm meter, or low voltage continuity tester.
You can not test ohms impedance with an ohm meter. You are only testing continuity and shorts. I encourage every one to test all coax runs for basic continuity, and shorts. You can not do such tests with the coax hooked up to anything. Some baluns and antennas will test as direct short at DC.
https://www.youtube.com/watch?v=9AE9F-TLIjk
Etekcity Digital Multimeter (DMM) Multi Tester Voltmeter Ammeter Ohmmeter - AC / DC Voltage, DC Current, Resistance, Continuity, Diodes, hFE Tester with Backlit LCD - - Amazon.com
http://www.amazon.com/Sperry-Instru...1_3?ie=UTF8&qid=1434744177&sr=8-3&keywords=co
Some televisions and converter boxes have very useful signal quality meters. I've seen others that are worthless. I will address the meter question a bit more when I have more time to chase down some links. Yes I've seen some reference to some low cost broadband SDRs that might be of use. I'll chase that down when I have more time.
Steve
Thanks Steve, I will do a Resistance test on the cable with my Multimeter tonight, and report back.

Our TV doesn't have any indication of signal quality of strength. I wish it did, as I may not have posted with this information.

Thanks, will look out for those links.
 
U

Unregistered

Guest
#6
Morrie,

As Steve mentioned, some TVs and Converter Boxes have useful signal quality meters but please understand they are not signal strength meters. A very low signal strength with a high-quality will rate number approaching 100 -- but -- a low-quality high signal strength will rate with much lower numbers and your tuner may not be able to decipher a poor quality (confused) signal.

Antenna height is usually the key to good reception but (example) 20 feet above ground level may not be as good a location for your antenna whereas 18 feet or 22 feet might be ideal.

The damaged area of the coax may be acting as an antenna, allowing signals to enter or exit the coax and it certainly is not waterproof: water entry will kill your reception so your damaged coaxial cable should be repaired or replaced with new RG-6. If you are certain there has been no water entry, you could cut out the damaged areas, install new 'F' fittings and use a 'double-female' connector to complete the job: the cost would be minimal. Radio Shack, Fry's, even Lowes has those fittings.

Next, your metal framed patio table is likely having an unpredictable effect on your antenna. TV antennas should be located at least 3 feet away from any metallic object and as far away from metal roofs, metal siding and metal gutters as reasonably possible.

If you are interested in other recommendations, please post the URL result of your free antenna survey for us to study. Be sure to include the maximum possible height above ground level where you could install your antenna and use your actual address: that site will automatically conceal your address for your security. TV Fool

Jim
Hi Jim,

I am aware of the difference between signal strength and quality, but correct me if I am wrong, that the former is in my control to change, but the latter is very much out of it, assuming antenna, cable, or tuner are situated (as applicable), and working as well as they could (i.e., it is caused by interference coming from somewhere along the transmission path).

RE: Antenna height - How then can one determine ideal height?

Given use of money to replace the cable wouldn't be the best use of what I am living off especially if I could get away with just splicing the cable if there is no water ingress, the question seems to be how to determine/test if water is likely in the cable (somewhere? I wasn't aware there was enough space in the undamaged portion, a.k.a specced design, of the cable to have water seep in)?

I didn't realise that kind of distance between antenna and other metal was required. While working on this problem I have relocated it so it is sitting on a bunch of cinder blocks (front/smaller elements) and a couple of plastic deck chairs (back), at least 3 feet away from the patio table and any other metal object.

Find my TV Fool link below, with close-as-I-could-get-it height measurement. I try to stay off the roof as much as possible, and couldn't find anything long enough to brace the measuring tape. So had to try and keep it taught for as long as possible from the ground, then again from a second story window, adding a little to account for the rest of the pole that I couldn't keep the tape taught enough to get up to.
TV Fool

Finally, any thoughts on question 3?

Thanks,
Morrie
 
#7
Jim covered a lot of ground in his reply. You really do need to replace that coax if possible. I've done quite a bit of antenna work helping people of very low income acquire basic local television reception using very simple antennas built from recycled materials, old TVs and used converter boxes. I don't know about your area but where I live I've sometimes been able to get very low cost coax, baluns, splitters and other connector for some of these projects from Habitat for Humanity, and other local thrift shops. Sometimes even new parts, and coax tools.
With analog TV signals you could get by with all kinds of sloppy coax and antenna connections with digital signals all kinds of strange problems can result from poor or intermittent connections. Having worked with a lot of junk parts I have seen poor coax runs selectively eliminate one strong channel while passing the rest of them with no problem. High VSWR on a feed line was something we could largely ignore with analog signals that can cause complete signal loss with digital signals. It should not have been ignored with analog signals, and did create problems but most of us didn't really know any better. I'm well aware of the situation of being unemployed. Working with salvaged junk and all of the problems it can cause. With the time, and money spent to CORRECTLY repair that old coax you could buy new coax.
If your signals are indeed as strong as the predicted in the posted TV Fool report unless there is some severe nearby blockage you shouldn't have problems.
 
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#8
Now I'll answer question 3 from your first post a bit better then I have so far. Low cost Satellite signal meters measure signal strength from a broad block of signals from one satellite after it has been filtered down to that block of frequencies, greatly amplified, and block down converted to a lower frequency by the LNB. Such simple meters do exist for OTA, but they are pretty worthless for anything more then getting your antenna pointed in the right general direction. They are sometimes used by people with RVs, but your probably better off just using TV Fool to get the antenna pointed in the right general direction. There are good high dollar meters available.
I've never used an ATSC USB stick but I did do some research it was not difficult to find a list of them that will run on Linux. I only checked into two of them to find out if they provided some sort of signal strength reading as best as I could find out on a short simple search the answer was yes. I've currently no need to research the subject farther I'm not looking into purchasing one. I do run Linux most of the time.
ATSC USB Devices - LinuxTVWiki
Of the 10 or so different TVs and converter boxes I've work with in the last three years I've only ran across one TV that didn't have a signal meter that I could find some of them are buried pretty deep in the menus, and one converter box that had a totally useless signal meter. Very few of them will give you a relative signal strength reading on a signal that is below what is required to lock. One exception is the Zenith which will show strength of a weak signal then switches to a signal quality meter when the signal locks. While it has been sometime since I've researched it some of the converter boxes had very good signal meters. I personally would like to have a better signal meter then the ten bar display buried in the menu on the Samsung I use for testing my latest antenna builds. I always keep a watch for used converter boxes, but there are few of them around in this part of the country.
Steve
 

Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#9
Hi Jim,

I am aware of the difference between signal strength and quality, but correct me if I am wrong, that the former is in my control to change, but the latter is very much out of it ...
NO! Neither signal strength nor quality are within your control, however, you can hunt (move your antenna up / down / right / left) until you find the best location for your antenna to be permanently located. Ignore "the idea of" signal strength (since you have signal and that is all that matters) and hunt for the best quality signal. Your meter will report signal quality and that is the key to dependible reception.

Jim
 
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