[Hitechluddite]

I have been comparing specs on all the different flavors of RF-6 that Newark lists and I'm at a loss as to why the big price difference given that the published loss factors are nearly identical. I know some is direct burial and some is quad sheild etc. But why would some cost almost $1000 for a thousand feet ans some $180 with identical loss figures, velocity factor etc? What am I missing here? They are all belden brand cable....

https://www.newark.com/w/c/cable-wire-cable-assemblies/coaxial-cable/prl/results?st=rg6%20patch%20cable

 

[majortom]

Some are using copper clad steel, some are using solid copper.
Some use aluminum for the braid, some use tinned copper for the braid.
The link you provided did not filter down to just Belden as you mentioned. And did not care to weed thru every choice.

But, filtering down to simply Belden 500' Reels and "in Stock" I am left with only two choices.
eg - if it's not in stock, why show it to me, why would I care.

Both are solid copper center conductor, one listed as $189.53, the other $472.99
The more expensive one uses tinned copper for the braid, instead of aluminum, thus has nearly half the DC resistance in the braid, which may be critical for someone powering electronics at the far end over extremely long runs.
(eg satellite antenna electronics, motors, etc.).

 

[Hitechluddite]

That's weird when I click the link I get 13 types in stock.... So from what you saw the added copper shielding that gives lower DC loss than RF makes for the higher cost, that makes sense but it's interesting...in that DC resistence is a secondary concern in most applications.

 

[majortom]

Again for extremely long runs, If whatever is at the other end doesn't even function or is unreliable because of the DC voltage drop, what good is it?
Run some simple Ohms law calculations.

 

[rabbit73]

This is the Newark filter that I used for Belden RG6:
https://www.newark.com/c/cable-wire...ial-cable?brand=belden&coaxial-cable-type=rg6

Majortom is correct; the price is based on manufacturing cost. Look at the specs in the datasheet.

The DC resistance can be important for DC voltage drop when a preamp is used. The preamp current has to flow through the center conductor AND the shield.

 

[majortom]

further...
DCR may be of secondary concern for you.
However, it may be of primary importance for the next guy searching.
Which is why your given a choice.

 

[ExDilbert]

There are other issues with aluminum. It oxidizes very quickly, almost instantly, and aluminum oxide is an insulator. When carrying any significant amount of current, it should used with connectors designed for contact with aluminum or the connection may fail. For a reliable installation, copper or copper clad aluminum should be used, especially outdoors. Copper clad steel is is sometimes used for the center conductor. It also suffers from higher DC and low frequency AC resistance and is more difficult to work with due to steel's hardness.

 

[Jorgek]

If your plan is to run cable outdoors be sure it is UV resistant and rated as such.. Not all cable is.

 

[Hitechluddite]

This is the Newark filter that I used for Belden RG6:
https://www.newark.com/c/cable-wire...ial-cable?brand=belden&coaxial-cable-type=rg6

Majortom is correct; the price is based on manufacturing cost. Look at the specs in the datasheet.

The DC resistance can be important for DC voltage drop when a preamp is used. The preamp current has to flow through the center conductor AND the shield.

Do you have any idea if most preamps are binary i.e. on or off or do they have varying gain dependent on input voltage?

 

[ExDilbert]

Low voltage probably won't affect gain. They would typically have a voltage regulator to allow for some voltage drop. Below a certain input voltage, the overall performance could be affected or it might just stop working.

 

[Hitechluddite]

Low voltage probably won't affect gain. They would typically have a voltage regulator to allow for some voltage drop. Below a certain input voltage, the overall performance could be affected or it might just stop working.

Just curious, the circuits could be built either way, at some point I would imagine that the noise factor would rise under lower input voltage to the point that it would hurt more than help.

 

[rabbit73]

There is no standard design; they vary. The important voltage is the voltage to the preamp at the preamp, but this is difficult to measure because you need access to the center conductor when the preamp is connected. I use a T-adapter:

Some preamps use a 5VDC power supply, like the Winegard LNA-200 and the Channel Master 7777HD. I was helping someone with the 7777HD that wasn't working the way it should; he had a very long buried coax line to the preamp at the antenna. Channel Master recommends keeping the coax to less than 100 ft, but of course the voltage drop would depend upon the coax used. I decided to make some voltage vs performance tests:

The performance of the preamp suffered when the voltage at the preamp was below 4VDC:

It would seem that the 7777HD preamp can compensate for voltage drop down to 4VDC.

His buried coax was able to pass the signal, but not the full voltage to the 7777HD. I suggested that he replace the coax, but he didn't want to do that. He put a solar powered battery at the base of the tower.

 

[ExDilbert]

Another solution would be to use a higher voltage power block to compensate for the voltage drop. In the above example, a 6v source would compensate for the 1v loss and provide 5v at the preamp. Considering how easily a 1v drop can be created over cheap coax, I'm surprised that Channel Master didn't provide a little more headroom.

 

[Hitechluddite]

Good Info! That should be easy enough to check I have a whole bag full of wall warts. If I have to I can use a 12V and wire in a 7808 regulator IC. Next time I'm at the farm I'll get the exact number of Beldon I have and get the specs on it. I know it's aluminum and it has braid and foil....I am running a little over 150'. I'm thinking I'll drop my tower with the winch this spring and take my time rebooting the TV antennas.

 

[cj47]

To sum up the OP's questions;
"you get what you pay for"

The no-name (of fake names) have little if any QC.

I bought some closeout RG6 "satellite" cable. When I 'sweped' the length, it came up a dead short. I found a 15' section that had no dielectric between the center and the shield. In the injection process, there must of been a 'air pocket' in the supply line and it didn't get injected even thou the center, braid & outer jacket was.

 

[tvmaster]

Again for extremely long runs, If whatever is at the other end doesn't even function or is unreliable because of the DC voltage drop, what good is it?
Run some simple Ohms law calculations.

Can you define ‘extremely long runs’ in feet or meters? My 20-year-old coax is beginning to disintegrate, and it’s time to replace...

 

[rabbit73]

Can you define ‘extremely long runs’ in feet or meters? My 20-year-old coax is beginning to disintegrate, and it’s time to replace...

Channel Master says to keep the coax run less than 100 ft when using a preamp, but of course that would depend upon the coax used.

If you don't use a preamp, the important consideration is the signal attenuation in the coax between the antenna and the TV for UHF. That attenuation directly subtracts from the antenna gain.

If you use a preamp, the signal attenuation in the coax and the voltage drop for the preamp are both important.

I would consider anything over 200 ft as extremely long.

This system by Calaveras has a coax feedline 575 ft long between the preamp and the power inserter.

RG6 10 ft
RG11 75 ft
1/2" hardline 480 ft
RG6 10 ft
Total 575 ft

 

[Hitechluddite]

I have about a 150' run of Belden 9114 RG6 and am running a CM 7777 Titan preamp. I have a T connector and I will measure the voltage drop on this run during Spring break when I drop my tower. I will record the results and post here for future reference.

 

[Jorgek]

Specifically, what kind of T connector are you using?

 

[Hitechluddite]

Same kind rabbit pictured earlier in the thread.