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Eventually I might be attempting some deep fringe stations 100+ miles away, 2EDGE and TROPO. At any rate, a db here or there might make a difference. I see scrap cable of the commercial variety up to an inch or so in diameter, but it is all 50 ohm and actually the loss is higher than 75 ohm in some cases. So... in sifting through the digital ether it seems that the lowest loss 75 ohm I'm finding is LMR-600-75. What do the experts say, other than it is not worth it?

Looking to replace the main line into the house and earn back the db, I'll be losing from injecting/combining.

Been busy and everything is running solid through football season - which was worth all the hassle.

Thanks,

Flint
 

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I'm not an expert at all but I always say: like in the computer world, your setup is as good as your weakest link. I think for digital television satellite, OTA good quality quad-core RG6 or RG11 is all you need. I think each coax has its purpose. There is only so much you can get from the cable. For OTA DXing best quality antenna with good quality rotor, strong must, as high as possible, low loss high quality splitter/combiner, quality water and moisture tight connectors, good quality low loss pre-amp, are as important as coax. It's a nice hobby but you have to balance the cost and common sense.
LMR-600-75: " Lower attenuation specs than RG11, this cable is perfect for broadband video and specialized 75 ohm applications." There you go. In my opinion it is over kill for OTA as with the low television frequencies it will not pull any more signal.
Let us know of the results. Run your setup with your current RG11 and than swap it for your expensive LMR-600-75.
 

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Looking to replace the main line into the house and earn back the db, I'll be losing from injecting/combining.
If those losses are before the preamp, lower loss coax downlead will not compensate for them. If they are after the preamp, the preamp gain compensates for them.

Commscope makes 75 ohm hardline in 1/2, 5/8, and 3/4 inch used by CATV systems.
Hardline
3/4 inch (.750) example
5204003 | P3® 750 JCA
Looking to replace the main line into the house and earn back the db, I'll be losing from injecting/combining.
I'm inclined to agree with ogorek. The preamp at the antenna determines the system noise figure, so the preamp gain takes care of the downlead loss.

You can run your own analysis of system losses and net noise margin with software that I can link you to. Calaveras uses hardline for his long run and uses a high gain low NF preamp at the headend. You only need enough preamp gain to offset coax attenuation; any more risks IMD from partial overload from the strong signals that will wipe out the weak ones.
http://www.aa6g.org/DTV/index.html
http://www.aa6g.org/DTV/ABD/Antenna_Block_Diagram.html
http://www.aa6g.org/DTV/Reception/tvfool_nm.html
http://www.aa6g.org/DTV/Noise/noise.html



What the diagram tells you is that you can forget about signals with a NM lower than -15 dB because they are buried in the noise; antenna gain can not "pull them out of the noise." It also shows that only antenna gain can make the NM more positive to overcome the preamp NF.

If the antenna gain is only 16 dB, then the weakest signal you can receive is NM -13 dB. Any loss between the antenna and the preamp input subtracts from the antenna gain.





You could probably get the system noise figure down to about 1 dB with a halfwave coaxial balun or a 75 ohm direct feed antenna with choke balun and a preamp with a NF of 0.4 dB.


And if you used an antenna with 16 dB gain, you would be just at the edge of the Digital Cliff:



More discussion on the tvfool thread
http://www.digitalhome.ca/forum/81-over-air-ota-digital-television/103476-tvfool-canadian-discussion-20.html
 

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Good points all. Must say when folks break out the math, I just fog over. Don't get me wrong I see the math, but too many unknowns as it is all home brew and no way to measure the real strength before I start. As always, I guess I'll just see what happens. You're looking at higher gain amp than what I was looking to.

Now if I can ever find Post 26744...
 

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Post 26744 is on another forum; I'm not allowed by the rules of this forum to give an active link to it, without permission from stampeder.

I assume you want the Net Noise Margin calc.

I'll try to drag it here.

Maybe this will work.

As a DHC Supporter I am allowed to make an attachment, but I can't do that one because it is an xls file.

Plan B, attach as a zip file.

That didn't work very well. It gets converted to a php file. To convert a php file to xls, you have to change the file extension to xls. PITA

Well, you can copy the link by hand in the gray bar. That works; it takes you to post 4 where the file is attached if you can't get it from my attachment here.
 

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Net Noise Margin Calculator & System Noise Figure Calculator

I think I got it right this time. I downloaded the original file for the Net Noise Margin Calculator from an attachment by GroundUrMast that said 10K xls file, but it downloaded as a 10K php file.

I changed the file extension to xls, zipped the file, and uploaded it as an attachment to this post.

Download and save the attachment; it will be a 3K php file in Downloads. Change the file extension to zip, and extract the file which should be a 10K xls file for the calculator.

LINE 15 has the wrong label; it should say Net NM (dB).

The System Noise Figure Calculator by holl_ands and majortom is file 10 on this page:
OTA Reception Files

which should be here:
XLS 10 of 22, OTA Reception Files
 

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Eventually I might be attempting some deep fringe stations 100+ miles away, 2EDGE and TROPO. At any rate, a db here or there might make a difference.
I've found the number one factor to improve dropouts on weak stations that far out is antenna height.Big difference from 30ft to 65ft,at least where I live.If I could find a good deal on a 100ft crankup,I'd have one.
 

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True enough in most cases, and TVFool lets you plug in different heights to see what might be possible. As the fighter pilots say: "Altitude = Options". This thread is specifically about OTA Cabling, though. :)
 

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I calculated INCREASE in System Noise Figure (NF) for various Low-Loss Cable Types (plus RG-6 for Comparison), presuming a very long 500-ft Cable Length after a 20 dB Preamp with NF=3. Note that COST of LMS-400-75 is about the same as the SKED40 PVC Pipe I would recommend you PUT it in for protection from the elements...and stepping on:
http://www.digitalhome.ca/forum/81-...amps-preamps-distro-amps-284.html#post2729890
First Link below was used for the Cascade NF Calculations....which can be adapted for any particular situation.

COAX CABLE LOSS AND INCREASE IN SYSTEM NF FOR 500-FT AT 700 MHz:
Cascaded Noise Figure Calculator [Second Stage is Coax with Gain=0, NF=Loss]
Coax Calculator
Welcome to Times Microwave | Coaxial Cable - Attenuation & Power Handling Calculator

RG-6: About 40 dB, depending on Mfr.
17.1 dB NF Increase with 20 dB, 3 dB NF Preamp [NOT SUITABLE]

RG-11: About 20 dB, depending on Mfr.
1.7 dB NF Increase with 20 dB, 3 dB NF Preamp

Times Microwave LMS-400-75: 16.2 dB + Connectors [75-ohm, 0.405-in O.D., 6.8-lbs/100-ft]
0.8 dB NF Increase with 20 dB, 3 dB NF Preamp
https://www.timesmicrowave.com/documents/resources/LMR-400-75.pdf
Times Microwave LMR 400 75 Ohm Low Loss Coaxial Cable - Per FT | TriangleCables.com [$1.27/ft up to 499-ft + S/H]

Times Microwave LMS-600-75: 10.2 dB + Connectors [75-ohm, 0.59-in O.D., 13-lbs/100-ft
0.2 dB NF Increase with 20 dB, 3 dB NF Preamp
https://www.timesmicrowave.com/documents/resources/LMR-600-75.pdf

Andrews LDF4RN-75A Heliax: 8.7 dB + Connectors [75-ohm, 1/2-in O.D., 16-lbs/100-ft]
0.1 db NF Increase with 20 dB, 3 dB NF Preamp
LDF4RN-75ALDF4RN-75A - Obsolete
 

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Velocity Factor

Is there any issue with connecting together 2 40 foot sections of RG6 coax that have different velocity factors?
 
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