Is Stretching TV Antenna Wire A Problem?
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- Опубліковано 6 тра 2022
- tvrepairinformation.weebly.com/
I recently had a customer call me to complain that some of his TV channels were missing, and what I found had me wondering if bending, kinking or stretching TV antenna wire is more of a problem than I've ever realized since running new coax solved the problem.. If you have had an expereince like this please share your experience.
On a long run of RG6, 150' is about the max length Commscope says your can retain reliable signal. Any longer a much more expensive and 3 times thicker industrial coax is advised. But at the extra cost and hassle with special connectors, customers usually decline. A tech also knows the thick teflon coax is a big hassle installing. The customer has to be willing to front the cost.
I was suprised to see how strong the signals were about 300 feet away from the antenna without an amp.
The length of the cable matters if the impedance is not properly matched e.g. with a termination resistor in the wallsocket came to my mind.
I was made to understand the distance between the core wire and the shield is what made it a ? 50 Ohm ? cable. Any change in that distance - ie bends, dents, crushed, and stretching changes the Ohm reading and therefore the efficiency of the frequencies passing through it.
Yes that's pretty much what I figured had taken place., TV coax impedance whould be 75 ohms. Perhaps it's not as critical with a short length of coax, but withh 300 feet of wire I'm sure it's far more critical.
@@GrantsPassTVRepair I am amazed that you do not need a preamp for the long distance Grant.
@@victoryfirst2878 I was equally surprised I didn't need a preamp. with 300 feet of coax. Perhaps it had something to do with the low RF noise at the customers location.
@@GrantsPassTVRepair I have to agree with you Grant. That is very unusual for certain. Hope you can make another video young man.
Grant keep on chasing money. That is what keeps everyone afloat. As for the coax cable dieing, the same thing happened to me but it was lightning strike that burned out the inter conductor. The TV stopped working and my mother said what is going on with the TV. I checked the wires with a run of 150 plus feet. There was no inter wire most of the way between the ends of the cable. Also, the cable was really extra flexible about ten feet from each end. Thank heavens for the grounding blocks which saved the day. Both were just fried. I used two grounds, one at the antenna and another at the home entrance. Ben Franklin really know what he was doing with lightning rods. Look forward to your new videos. I always learn something from you Grant. Thanks a bunch for the knowledge. Peace too. vf
Definitely understandable, it got stretched by the trees, there's a lot of strength in those trees when they move on windy days, not to mention the growth will snap steel cable, so it's feasible that coaxial cables will be like a piece of straw...👍
Best wishes Dave.
Frank.
Thanks Frank. I think you're right about the stretching issue.
@@GrantsPassTVRepair The only way to confirm this would be to replicate the problem.
Hi, yes if you just stretch the wire in a small area you will notice that if you feed signal and measure with a field strength meter that there will be a drop of signal on various frequencies. This is not as linear thing but it could lose perhaps 3db at 200MHz and maybe a 10db loss at around 600MHz and then further higher maybe a gain a loss of 3 or 4 db at around 800MHz. It just changes the entire property of the coax as the wire is stretched and the distance between the centre and braid distorts. Also very sharp bends can cause a similar phenomenon. And also coax that gets old and hardens also has its properties change. I am referring to RG6U 75 ohm coax.
That seems like the only logical explanation. Thanks.
@@GrantsPassTVRepair
- Yes, stretching of coax would fall in the category of coax cable degradation over time issues,
or
- there was simply a hairline crack in the coax somewhere (due to coax being bent or kinked etc..by nature/animal handling etc..just a thought anyways since you mentioned all the channels were gone then came back when a new cable was tried.
or
- simply , initially used a defective, problematic, or bad quality (aka: a lemon) coax cabling.
If you use long cable, sometimes due to weather, the signal gets too low.
For long cables ALWAYS use a signal amplifier, even when the quality of reception looks good without one.
Water in the cable is not an issue. Maybe defects of fabrication in it. But that's rare. Very cheap coaxial cables are a problem sometimes, but a signal amplifier corrects many imperfections.
Yes I normally would have used a preamp, but we had surprisingly strong signals which I verified using my signal meter.
Grants Pass / Yes, I know. But sometimes because of the bad weather the signal becomes low, that's why an amplifier is always king.
@@mikel4879 If you have boarder line signals I would agree to using an amplifier, but the down side of using an amp is you're adding one more component that antenna that can go bad, and since a bad amplifier is worse than no amplifier. I only use one where the signals are weak enougn to justify the need.
Grants Pass / You know what's better in your case.
What I just told you is from my long experience.
@@GrantsPassTVRepair Cannot dispute a signal meter.
I would imagine the wind plays a major role in stretching coax, those trees moving in different directions all the time has to have an impact on it.
I would totally believe that stretching the coax cable would wreak havoc somehow.
Interesting. I would guess the stretching action changed the diameter of the insulator between the core and the sheath. At such a long run, that might dramatically change to overall capacitive reactance of the coax. Thus attenuating the signals.
What i have learned is that the isolation (dielectric) between the inner conductor and the outer braid can get damaged,
when bending the wire in a too narrow corner. Some short coax cables that are sold for connecting a settopbox (Digicorder) to a tv, are bend very narrow
in the blister package, and give later on blocks in the screen image quality with digital tv.
Another test maybe, is a capacitance measuring between the inner conductor and the outer braid ?
I once had a short 4 foot coax jumper between a TV and an antenna which caused one of my channels to be attenuated, so I believe what you're saying is right on.
Impedance change in the coax is a bad thing.
You can dial in a value that will end up being an electric short at a band of frequencies, while still having good DC values. It is hard to show the failure to a non technical person, when the DC values say the coax is still good!
I get the impedance issue. That's the only logical conclusion I can come up with.
That would make sense if the transmission line becomes electrically longer you are adding capacitance which will change the phase angles and throw your signal at the other end out of phase. If this is digital than perhaps it was enough to blink out the signal. It would be an interesting experiment to run a signal through diferent length coaxes and scope them out for comparison
Not really sure of what you mean. Can you clarify that statement Q ???
@@victoryfirst2878 all transmission line whether it be a guitar cable or tv coax has a capacitance per foot rating. This capacitance per foot is 'parallel capacitance'. A smith chart is a visual representation of a phaser, it shows where the total impedance point is at a given frequency with a given resistance, capacitance and inductance. When you 'add' length to any transmission line you are adding parallel capacitance. On a Smith chart, parallel capacitance moves in a clockwise path whereas series capacitance moves in counter clock wise fashion. At the length that he cut his coax which was 300ft I believe he said he thought he would have needed an amplifier but it worked out he didnt. My theory is he must have cut it just at the right length where the Smith point ended up at resistance R with no +-J therefore no reflect or losses. In the digital tv world you either have the picture 100% or you have blue screen. I believe that at that length of 300ft, when the coax stretched, it added enough capacitance to cause an imbalance in the system or a mismatch causing the signal to be lost. Long answer but steps have to be covered if you are unfamiliar with impedance matching. Hope that helps.
I would love to know that answer. Then we can spread it around.
@@user-su5sq5ib3i As a matter of fact. Shame you are not next to me I would shake your hand for explaining that fact. Now it makes perfect sense. YOU THE MAN AND THANKS. vf
Did you check the old coax, you might find rubbing causing water ingress or animal damage, just a tiny break in coax and water screws things up amazingly fast. Trees moving will damage coax quite fast, even rub through the coax.
The old coax and it looks perfect.
@@GrantsPassTVRepair Wow!🤔
I had a two-meter antenna that had -Perfect- SWR, but did not work. I found the connection at the antenna broken and not even connected!
Further discovery that water ingress had rotted everything everything inside the RG-8 and it was just absorbing all the RF.
@@KeithKenobi Yeap. Water ingress is a total killer.
this is best to use RG6 Standard Shield with Messenger steel suport wire
Very interesting. Some RF channels got impacted. A one-year-old coax cable is basically new. Two questions: Did you use RG6 or RG11? What signal meter are you using?
Hey from South Africa great to see you again I've been following your excellent videos for years now.
This is an X-File that's for sure.
Normally with impedance mismatch you will get a suck out because of the standing waves.
Silly question but did you use 360 crimps on the ends as I have seen water wick into the cables and you get oxidation which will cause a high end roll off. Bad connections cause a low end roll off because the higher frequencies can jump the gap due to the "capacitive effect". Are his channels VHF or UHF?
What you can do is try in your shop. If you see the same thing then cut in half and you should be 3dB down.
If you find one half work and the other doesn't then you have your problem half.
If you can't see any damage along the cable then I suspect water has wicked in.
Let us know what you find as Enquiring minds want to know :-)
Keep well
I use F connectors that have an O ring and silicone gel to keep the water out of them.
Could you measure the characteristics of the line with a (nano/lite)VNA? or a MFJ259 antenna analyzer to validate the hypothesis?
Did you check the impedance in either end vith an VNA. Something like the NANOVNA would have been handy.
Bury it like the cable companies do with the same type of cable!
Question is, what will you do with the dodgy 300' of coax?
I thought it might be interesting to run an impedance test on the coax to see if I can verify the issue for an additional video.
Well Grant thats very interesting and no amplifier either on that long stretch, How did u brace the coax on the trees this time??? its gonna cost u money replacing it every so often under warranty. BTW i would say the impedance was choked out of the coax... the dialectic cant be kinked so I would summarize to the fact it had reduced in size along the run where it stretched the most and good bye to spectrum frequencies in the tv bandwidth.
BTW, maybe u need a signal amp powered by a 12v10ah agm batt and a 30watt solar panel.
This time I left the wire on the ground, and the customer plans on having someone put it inside a pipe.
@@GrantsPassTVRepair good idea, pvc pipe is ok to do the job, but i suggest an access point every 1000ft.
@@OffGridAussiePrepper It's only 300 feet of coax, but it might be interesting to test small sections of the coax to verify the impedance issue.
They probably didn't grow, the wind probably blew perhaps?
Whatever the case may be it was another lesson learned in the school of hard knocks.