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Guest Message by DevFuse

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Attenuators versus Splitters


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7 replies to this topic

#1 OFFLINE   ZandarKoad

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Posted 22 August 2014 - 03:33 PM

Is a two way splitter (with one port capped) the same as a 3.5 db attenuator? Would a four way splitter with three capped ports serve as a 7 db attenuator, etc.?

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#2 OFFLINE   bflora

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Posted 22 August 2014 - 03:46 PM

Yes.



#3 OFFLINE   AntAltMike

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Posted 22 August 2014 - 03:52 PM

Why do you want to attenuate your signal path?

 

One word of caution.  Sometimes, when you put a terminating resistor on a splitter port, it inadvertently shorts the DC power in that coax.

 

 



#4 OFFLINE   ZandarKoad

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Posted 22 August 2014 - 04:41 PM

Why do you want to attenuate your signal path?


Same reason attenuators exist.

#5 OFFLINE   harsh

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Posted 22 August 2014 - 05:36 PM

Somebody's amp was a little to hot for the application. ;)

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#6 OFFLINE   ZandarKoad

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Posted 22 August 2014 - 07:05 PM

140+ units across seven buildings - something's going to be too hot.

#7 OFFLINE   slice1900

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Posted 22 August 2014 - 08:35 PM

Typically in a large install if you have problems with signal "too hot" it is because you should be using taps, not splitters.


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#8 OFFLINE   AntAltMike

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Posted 22 August 2014 - 09:17 PM

I used to service three highrise buildings that had single, stacked "Sat A" trunklines.  They used 4-port taps, but misused them.  On the top floor, there was a -16dBx4 in series with two -12dBx4s, then there were two -12x4s on each of the next five floors.  In other words, there was a structural signal differential of nearly 30dB between the top floor and the bottom of that branch.

 

The other funny things about that installation were 1) they used RG-11 with $3.00 connectors for the 6" jumpers between the two 4-port taps on each floor and 2) some of those nice compression connectors had been mis-installed, such that, they hadn't shoved the coax deep enough into them to penetrate the center conductor pin seizure sleeve, so if anyone breathed on them too hard, they would disrupt the signal.

 

With one MATV highrise, I had once customer whose building had -9dB taps in each cable closet.  That only got them about a 20dB structural differential.

 

I have one eight story hotel with riser wallplate wiring where they put 3-port balanced splitters on every floor with back-to-back wallplates, such that, the eighth floor gives 1/3 to each plate and passes 1/3; the seventh floor gets 1/9, and 1/9th and passes 1/9, minus coax loss, the sixth floor 1/27, the fourth floor 1/81, etc etc. They also still have some VHF only splitters in their ceiling that tilt about 20dB between channel 13 and cable channel 54, but they won't let me cut into their plaster ceiling to find and replace them.

 

I used to have one hotel in Baltimore that had 7 wallplate horizontal loops that I had perfectly balanced with taps, but they wanted to change from off-white plates to white, and the only white ones they found had center holes instead of offset holes, and with some wallboxes, you can't squeeze "DCW" style taps into a center hole wallplate, so they bought mini two way splitters and installed them improperly, with the single port going through the wallplate and the two supposed output ports being used as one-in, one-out.  The loss that way is 20 to 25 dB each, and worse yet, that loss is not flat across the channel and it mangles analog signals.

 

Marriott used to prewire their MATV distribution such that they had home run apartment wiring, but used -12dB taps in each apartment, so they needed an amplifier on each floor.  Some company from New Jersey that knew nothing about MATV set up their trunk system using old fashioned Blonder Tongue ACA amplifiers that had separate preamps and power amps in them for about 50dB combined gain.  They fed about 20 to 30dBmV into each preamp stage, which overloaded it, and then jumped that defective preamplified signal into the power amp stage, which further overloaded it.  They then observed that it was somewhat less ugly if they left out the power amplifier and so they just "preamplified" the powerful trunkline signal and distributed that.

 

In my opinion, a lot of people doing MATV work should be shot.


Edited by AntAltMike, 23 August 2014 - 02:01 PM.

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