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SWM16 install question


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24 replies to this topic

#21 OFFLINE   veryoldschool

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Posted 28 September 2012 - 12:40 PM

Actually, a barrel isn't a barrel. It should be "high-pass" to "ensure" passage of all frequencies used within a Directv system. These are usually blue instead of white or clear on the inside, although the newer ones coming out are orange. I have done alot of troubleshooting of motel directv systems and those older barrel connectors are at fault 50% of the time.

I'd tend to say this was because of being old and worn out much more than the color of the dielectric, since it has no effect on frequency.
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#22 OFFLINE   dielray

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Posted 29 September 2012 - 05:04 AM

I'd tend to say this was because of being old and worn out much more than the color of the dielectric, since it has no effect on frequency.


The color of the dielectric indicates the frequencies the F81 is rated for. White/clear F81s are just rated for UHF/VHF. Yellow/Blue are rated for higher frequencies. Orange indicates passing DirecTV's specifications.

In practice many white F81s work fine for 2GHz.

Perfect Vision's Spec Sheets for each color:
White: https://www.perfect-...ets/PV05F81.pdf
Blue: https://www.perfect-...s/PV05F81HF.pdf
Orange: https://www.perfect-.../DTVF81I-05.pdf
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My thoughts and opinions are my own, and do not necessarily represent those of DirecTV, my HSP, or anyone else.

#23 OFFLINE   veryoldschool

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Posted 29 September 2012 - 08:09 AM

The color of the dielectric indicates the frequencies the F81 is rated for. White/clear F81s are just rated for UHF/VHF. Yellow/Blue are rated for higher frequencies. Orange indicates passing DirecTV's specifications.

In practice many white F81s work fine for 2GHz.

If the dielectric [constant] is the same, then the frequency range is too.
This is a QC thing and not really an electrical performance issue.

Here's the breakdown from those pdfs:

http://www.dbstalk.c...=1&d=1348926211

These are nothing more than a short transmission line, so the physical dimensions and dielectric constant determine their impedance.

The one on the right will have the same frequency range regardless of the color of the dielectric, because the dielectric is the same material.

The one on the left looks to be the worst, yet DirecTV uses them on the WB68 up to 2150 MHz.

The one in the middle has a larger center conductor, but also looks to have an air gap [lower dielectric constant] to keep the impedance at 75 Ohms.

Given that these are only about an inch long, the loss delta between all of them is going to be almost negligible.

Being damaged or worn out will have more affect than anything else, and it doesn't matter which one of the three it is.

If you work to a standard, follow it.
If "the boss says" use a pink poke-a-dot barrel, then use one.

If you're buying your own barrels and they're those on the right, don't waste your money on fancy colors.

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#24 OFFLINE   carl6

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Posted 29 September 2012 - 09:02 AM

The color of the dielectric indicates the frequencies the F81 is rated for.


This is a QC thing and not really an electrical performance issue.


Quality Control is the key here. In order to guarantee a barrel meets a specification, it is necessary to have manufacturing and testing processes in place that you don't need otherwise. It costs money to do that. To indicate a barrel meets a particular specification, a different color dielectric is used.

Just because a barrel does not have a particular colored dielectric doesn't mean it won't work at wider frequencies, it only means it isn't guaranteed to. In almost every case, the non-guaranteed product works just as well and is produced (and sold) at significantly lower cost.

#25 OFFLINE   veryoldschool

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Posted 29 September 2012 - 09:47 AM

Just a side note: I've actually paid $100/ft for coax (:eek2:) because it had special dielectric, but it was used at frequencies 10x higher than what is here.
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