3-way coax splitter - why are my legs rated at -7.5dB vs -7dB? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 9 Old 04-04-2019, 07:38 PM - Thread Starter
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3-way coax splitter - why are my legs rated at -7.5dB vs -7dB?

I am trying to to perfecting my cable signal. My house coax splitter has 3 legs (-3.5dB, and 2x -7.5dB).
Just wondering why -7.5dB vs -7dB?
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post #2 of 9 Old 04-04-2019, 08:16 PM
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Think of it as two splitters...You aren't dividing by three, you are splitting into two (3.5 and 3.5) and one of those is split to 7+7. So, 3.5 and 7 and 7. Same you would get if you had two splitters and hooked #2 to the output of #1

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post #3 of 9 Old 04-04-2019, 10:10 PM
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Quote:
Originally Posted by metropole View Post
I am trying to to perfecting my cable signal. My house coax splitter has 3 legs (-3.5dB, and 2x -7.5dB).
Just wondering why -7.5dB vs -7dB?
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Originally Posted by speedlaw View Post
Think of it as two splitters...You aren't dividing by three, you are splitting into two (3.5 and 3.5) and one of those is split to 7+7. So, 3.5 and 7 and 7. Same you would get if you had two splitters and hooked #2 to the output of #1
They are probably adjusting for the small loss of two splitters cascaded and assuming that adds another .5 dB.

There are some 3 way splitters that use more complex windings to produce 3 equal outputs with 5.5 dB loss. Antronix is probably the most common : https://www.amazon.com/CMC2003BH-3-W.../dp/B00VU61AKC
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post #4 of 9 Old 04-05-2019, 05:25 AM - Thread Starter
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Thanks. that must be it.

Franky, I might replace it with a two-way splitter anyhow. I have only two legs in use. Are there are certain brands that are preferred or features I need? i.e. any 1GHz two-way will do? Or I need more bandwidth?

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They are probably adjusting for the small loss of two splitters cascaded and assuming that adds another .5 dB.
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post #5 of 9 Old 04-05-2019, 02:09 PM
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Round-Off Errors....wishful thinking...and NOT telling the WHOLE TRUTH.

IF there were no Internal Losses, Splitters would have fol. Loss: -3.00 dB (2-Way), -4.77 dB (3-Way) and -6.00 dB (4-Way).

But in the Real World, there will be some Internal Loss, on the order of 0.5+ dB for 2-Way, 0.7+ dB for 3-Way and 1.0+ dB for 4-Way....TWICE that of a 2-Way Splitter (which is actually a series of 2-Way Splitters). This Loss varies with Frequency, typically increasing on the higher Freqs to (perhaps) 1.0+ dB of Loss for the 2-Way Splitter (NOT usually talked about in simple specs). So don't be surprised to see mfrs "Round-Off" their specs to nearest 0.5 dB...which likely represents a "typical" performance number, rather than a MAXIMUM number that should never be exceeded to pass their factory QA sample tests.

Holland Electrics (no relation to me) provides very precise Spec Numbers for their exceptional GHS series of CATV Splitters. GHS-3B is a true 3-Way Split, whereas GHS-3 is similar to what you have now, with one port at 3.9 to 4.0 dB and the other two at 7.5 to 7.6 dB (Typical to QC Max) across the entire UHF Band [and less on lower Freqs]. I BELIEVE these very precise specs, whereas what you see from other mfrs is NOT telling the WHOLE TRUTH:
https://www.3starinc.com/manuals/GHS..._Splitters.pdf
Compare to Holland's Budget HSU RF Splitter, where the specs are more Loosey-Goosey:
http://www.alltronics.com/mas_assets/acrobat/HSU-2.pdf

FYI: ADTech (Antennas-Direct Tech) posted measurements at 700 MHz and 1000 MHz for a variety of CATV and higher Frequency SAT Splitters:
https://www.avsforum.com/forum/25-hd...l#post42690538

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post #6 of 9 Old 04-05-2019, 03:19 PM - Thread Starter
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thanks!

So, if I downgrade to two ports, this woudl be a good choice?
https://www.amazon.com/Holland-Elect.../dp/B00P6VHLP0

BTW. regarding 1Ghz - does CATV need more?
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post #7 of 9 Old 04-05-2019, 03:28 PM
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Quote:
Originally Posted by metropole View Post
thanks!

So, if I downgrade to two ports, this woudl be a good choice?
https://www.amazon.com/Holland-Elect.../dp/B00P6VHLP0

BTW. regarding 1Ghz - does CATV need more?
Yes, this splitter will be fine. Personally, just stop a cable guy and ask for a 2-way splitter because you are removing a 3 way splitter. I would anyway. And 1 gig is what cable companies are running [at least in the major cities]

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post #8 of 9 Old 04-06-2019, 08:41 AM
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I have 2 of these and they're great.....
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post #9 of 9 Old 04-06-2019, 02:06 PM
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Quote:
Originally Posted by metropole View Post
Thanks. that must be it.

Franky, I might replace it with a two-way splitter anyhow. I have only two legs in use. Are there are certain brands that are preferred or features I need? i.e. any 1GHz two-way will do? Or I need more bandwidth?
Pretty much ANY 2-Way RF Splitter will get the job done....and a few tenths difference in Loss is impossible to notice.

CATV Max Freq varies, depending on upgrades in your area. Max of 800 MHz has been fairly typical, although many systems have upgraded (or plan to upgrade) to Cable Box Max of 1003 MHz...hence Typical 5-1000 MHz Cable RF Splitter gets the job done for old and new systems.

However, note that MoCA Frequencies are ABOVE 1000 MHz, relying on a very sensitive RF Receivers to get around the REVERSE ISOLATION going through multiple RF Splitters between Devices [e.g. DVR to DVR in Whole-Home Systems....and PC/HDD Servers to DTV/Disc-Players using DHCP protocol to Play Media Files]. In my experiment with Whole-Home DVR's, I had to try numerous RF Splitters before I found a set that had low enough Reverse Isolation to allow two-way interconnection....so the fol. RF Splitter intentionally designed for MoCA Compatibility may be needed in that situation:
https://www.amazon.com/Holland-Elect.../dp/B00P6VHLP0
http://www.mocalliance.org/MoCA2/spe...cs-150406d.pdf

BTW: When a Cable Co. installs a set of Whole-Home DVR/STB's, they will also install a MoCA Point Of Entry (POE) Filter to BLOCK that Frequency Band from leaking out into your Neighbor's MoCA Systems, such as following:
https://www.amazon.com/Filter-MoCA-C.../dp/B00DC8IEE6

PS: OTA TV only goes up to 698 MHz in most areas....but some areas [like San Diego & L.A.] have already shifted Channel Assignments so Max Freq = 608 MHz, with many more areas to follow in the near future. So standard CATV RF Splitter (typ. 5-1000 MHz) is also suitable for OTA [although you can NOT pass OTA and Cable down the same coax]. When YOUR OTA stations are changing:
http://www.tvanswers.org/when.asp

Last edited by holl_ands; 04-06-2019 at 02:44 PM.
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