recieve antenna coax,straight line(rg8x) VS segmented(rg6)

[fourthhorseman]

ok,
ive currently got the RS 20-176 vhf/uhf antenna on the roof,for RX ONLY

its about 55-60 feet,from radio to roof,using rg6 for 40ft,(2 segments,with an F coupler)
then another 17ft of rg58 with an f to bnc coupler.

so the currnent line is 3 segments..2 breaks.

i just got handed a roll of about 135ft of rg8x..pl259 at one end..cut at the other,ive got a some BNCs to fit it already..
copper shielded grey cable..(love the copper,,so easy to solder..)

ive read the rg8x has loss issues,but am i better off with the straight run of 8X vs the current rg6 and 58?

keep in mind,this is for receiving only.

 

[mmckenna]

On the surface, not counting connector losses, your 40 foot run of RG6 and 17 foot run of RG58, if I understood it correctly, has less loss than a straight 60 foot run of RG8x.

Where I'd pause for thought is you have 2 unnecessary connections in your current run that will add a tiny bit of additional loss, but more importantly add two places that can fail due to weather or poor connections. If you remove the small connector losses and some funkyness going from 75 ohm cable to 50 ohn cable, you likely wouldn't notice the loss differences between your current set up and the proposed continuous run of RG8x.
Where you would gain something is that with the continuous run of RG8x you are removing possible failure points in your feed line.

Personally, I'd put the 8x in to get a more reliable system, and accept the small increase in coax loss. Truth is, unless you are really on the fringes, you won't notice it.

 

[benbenrf]

mckennas' post makes a load of sense.

 

[kb2vxa]

Yes and no, first "connector losses" are insignificant being measurable only with laboratory equipment. This is a common myth impossible to dispel since it gets passed along with no supporting evidence and is believed.

Transmission line loss goes up sharply with frequency and becomes significant especially at UHF, horrendous at 800MHz so it should be a main consideration with any antenna system. If you can't go with RG8 foam dielectric cable that comes in many flavors such as LMR400 the second choice is RG6 quad shield used in CATV systems and available dirt cheap at Walmart for example. Quad shielding certainly helps keeping external signals and noise pickup out but requires slightly larger F connectors also available at stores that carry the cable. They usually carry stripping and crimping tools that do a neat and accurate job avoiding the knife and pliers mess. Adapters are available on line dirt cheap. Of course waterproof outdoor connections, water in the coax will ruin the whole thing.

 

[mmckenna]

Warren,

You seemed to misread the original post again. The OP clearly stated what he had in place, and what he already has as an alternative. He wasn't asking which cable he should be using, he was asking for input on which of the two choices would we suggest.

Connector losses are measurable without lab equipment, especially sloppy F connectors, but maybe the equipment that I have and you have are different enough to cause you to assume that. F-connectors are pretty awful things that show a bump on a TDR since they are not constant impedance like an N or 7-16 connector. They do well enough for customer drops and for handling broad band signals, but even in the cable TV industry they use higher grade stuff for the outside plant. Of course since so much of the outside plant is actually fiber, it's sort of a moot point. Snap-N-Seals and the similar types of connectors are the only ones that I would use outside, or even inside for that matter. The cheap crimp on ones do not seal the connections. Cable TV operators will replace those if they run across them in an installation since the risk of signal leakage is pretty high, and the issues that sloppily installed connectors can cause. Since the OP didn't state what sort of connectors he had, we shouldn't be making assumptions. RG-6 is pretty good stuff as small coaxial cable goes, and certainly useable for an installation like this. A continuous length of RG-6 with weather sealed connectors would work fine for this installation, but that isn't what he has. Given the choice between a segmented run of 2 different impedance cables with at least 6 connectors, one adapter and two couplers, likely most of them exposed to the elements, I'm confident in saying that in the long run, one continuous length of RG-8X would be preferred.

We can beat the coaxial cable choices and connector losses to death, but that won't help answer his question. The best thing to do is to accurately answer the question rather than let this deteriorate into yet another post that turns into another pointless argument.

 

[fourthhorseman]

Thank you for the feedback,

To clarify,

my set up is like this,,
antenna-pl259 pigtail to an BNC,then a BNC to F adapter--and an f coupler-20ft rg6-F coupler-20ft rg6 - F to BNC adapter,BNC connecter--about 17ft rg58--radio

a patchwork at best,and to confirm,after 2yrs up there Is water intrusion,cant tell how far,but no
amount is good..

i replaced the 3 segments and all the adapters with the single run of 8x,theres a noticeable difference,,signals seen a bit quieter,,

 

[mmckenna]

Glad to hear it worked out. A "quieter" signal makes it look like the water intrusion was getting pretty bad.

Coaxial cable isn't a lifetime install, it will fail over time, no matter how well you install it. It's common practice to "shoot" coaxial cables from time to time with an analyzer to show if things like water intrusion or corrosion is taking place. The equipment to do that is expensive and no where near the range for a hobbyist. They'll often do it to cellular base stations, etc.

Make sure you seal the connector at the antenna end really well. There are numerous sealing compounds and tapes that work. Secure the coaxial frequently to keep it from flapping in the breeze and damaging the outside jacket. Damage to the outside jacket will let the weather in.

In a few years, when you get the funds, look into upgrading your cable. As Warren said, RG-6 would be a good choice, LMR-400 would be better. It would cost you a bit more, but you can order from manufacturers that will cut to length and install the connectors you choose.

Glad you are seeing an improvement, and glad it worked out well!

 

[fourthhorseman]

yes Yes..made sure to seal the pl259.!after installing,i twisted it in nice n snug,then a finger of silicone cleanly round the connection..should do Far better then the crimp on Fs that were on there..

water was pretty invasive,,the inners of the couplers were rusting out..

thanks for the info & feedback!

 

[Techy]

Good to hear fourthhorseman, You can't beat a good clean install of new connectors and waterproofed connections. Mine was similar. Like mmckenna said I used the Belden Snap and Seal F connectors and those are great along with a filler in the F connectors called STUF and Belden NS-500 nut seals. Those crimp on and twist on F connectors are crap.
I have seen a major improvment on reception.

 

[mmckenna]

Yup, good coaxial cable and connectors can make a big difference. Imagine, now, stepping up to LMR-600, or 1/2 inch heliax from the previous set up you had.
It's pretty common to spend as much on the antenna system as you would on your radios in a really good install. Not trying to say what you have isn't sufficient, only that when you are budgeting for a new install, all to often people will shortchange themselves on the antenna side.
In other words, you can spend thousands of dollars on a new radio, but if you don't equally upgrade your antenna system, the results will be disappointing.