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Discussion Starter · #1 ·
in the past, my coax setup consisted of a 2 way splitter at the house entrance. 1 coax went direct to the modem, the other into an electroline 8100 drop amp. i had the 2 way splitter grounded to the ground from the main electrical panel. everything worked great but when using the scientific atlanta 8300hd pvr with component cables, i always noticed scrolling lines on the tv. ground loop, hum bars, etc. as they are often referred to. it was worse on some days more than others (or perhaps i just noticed them more). in any case, i sold the house and now am building a new one and would like to know if i can do a few things.


firstly, i will have about 14 coax drops to the basement. i would like to have them all hooked up to a drop amp so i don't ever have to do anything in terms of connecting cables to make them work. same idea as using a 16 port ethernet switch. all the runs go to it directly and then 1 run goes into the router, so all 16 drops will work whenever someone plugs into the wall. so my question then is this:


1.) electroline 8100 amp has been replaced with the 8300 which looks to be the same specs so lets assume i will be using this new model. since it only accepts 8 outputs, can i buy 2 of these and connect 7 coax drops to the outputs of the first amp, and on the last output, connect a coax to the second amp (like a jumper cable) and then connect the other 7 coax drops to the second amp. will this work no problem or will i have db loss issues, etc.


2.) i was just reading that humming lines could be a result of not loading the coax outputs (around the house on wallplates) and a reason to hum lines. could this have been the cause since i had 7 lines hooked up to my drop amp but only really used 2 tv's in the house and the other 5 outputs were not "loaded"?


any help is appreciated. thanks.
 

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It's the unused outputs of drop-amps and splitters that should have the 75 Ohm load resistors (terminators). The 8100 drop-amp has a ground screw connection. So that you can run a separate ground wire to the main ground point.
 

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Discussion Starter · #3 ·
hmm, okay well i remember adding a ground wire to the drop amp as well to see if the lines would disappear and no luck. im trying to avoid this in the next house so i don't know what else i could do. i can so though that the running lines disappeared when using a dvd player hookep up via hdmi. i know the component cables were not the culprit, although im wondering if adding a coax isolator would be the solution if i encounter it again.
 

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Discussion Starter · #4 ·
can anyone help on question #1 (re: daisy chaining the drop amps)
 

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It's a little hard to decode what you have and what you want. Inputs and outputs seem to be swapped. 8300HD STB and/or 8300 drop-amp. Try the splitter first then to the inputs of two drop-amps, that will give you 16 outputs.
 

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Discussion Starter · #7 ·

Quote:
Originally Posted by Speedskater /forum/post/17050955


It's a little hard to decode what you have and what you want. Inputs and outputs seem to be swapped. 8300HD STB and/or 8300 drop-amp. Try the splitter first then to the inputs of two drop-amps, that will give you 16 outputs.

okay, i've edited my initial post to make it a bit clearer in regards to inputs and outputs. so just to clarify then, the outputs of the amp (ports) are connected to the coaxes which are fed throughout the house and terminated into the wallplates around rooms (outlets). if i have these coaxes connected to the amp outputs (ports) but no tv connected to them, do i need to load these outputs at the wallplate location as well? the drop amp website says to do so (and i did not in my original installation).
 

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Discussion Starter · #8 ·

Quote:
Originally Posted by egnlsn /forum/post/17053134


Can't daisy-chain amps. The thing to do would be to install a 2-way splitter to feed both amps.

so i guess my best bed then would be to install a 3 way splitter at the house entrance. 1 to the cable modem, and 1 for each of the 2 drop amps. is this the only way? im a bit concerned with the -7.5db loss for the amps. the -3.5db loss for the modem is fine imo.


i believe the 8300 drop amp has a forward gain of 3db so using a 2 way splitter would be very close to the original signal. or is the only other way to ask the cable company to boost their signal to the home?
 

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If it were me, I would do a TAP for the cable modem connection (the value would depend on the signal levels at the cable modem), with the TAP leg connected to the cable modem and the OUT leg going into a single output drop amp. From there into a 2-way splitter then 2 8-way splitters.
 

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if you are worried about -7.5db loss on the 3way splitter then you have really weak levels to begin with and may just be amplifying garbage, get a pro out there, and get a better 3 way, either a 3x6 db loss across the board or a 3.5db loss and 2x 7db losses


if you arent using outlets, terminate them or u will introduce noise in the system which will cause issues but not humbars.


the humbar issue, get a ground loop isolator or an electrician to make sure ur ground isnt hot, i have the same issue with that box.


get an amtronics amp, +15 gain which would result in only a -1 loss plus cable loss. if not using digital equip on those outlets dont worry about the return but if u will be using modems and boxes on the outlets u probably will need an active return amp.
 

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Discussion Starter · #11 ·

Quote:
Originally Posted by dorito31561 /forum/post/17062817


the humbar issue, get a ground loop isolator or an electrician to make sure ur ground isnt hot, i have the same issue with that box.


i have read many stating that in fact it is this particular hd box introducing the problem but who knows really. im trying to eliminate as much as i can, but do you think its wise to put the isolator on the incoming line so all the distributed coax lines are filtered or just on the particular line that has the humbars?
 

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Discussion Starter · #12 ·
anyone?
 

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Quote:
Originally Posted by Anthony A. /forum/post/17049839


can anyone help on question #1 (re: daisy chaining the drop amps)

Channelvision will help you design the CATV system and give u the list of products numbers along with a diagram. You just tell them what components your using...usually takes them a few days and there is no charge if you purchase the goods from them.

(714) 424-6500 They are in Costa Mesa, Ca.

alan
 

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Quote:
Originally Posted by Anthony A. /forum/post/17085242


i have read many stating that in fact it is this particular hd box introducing the problem but who knows really. im trying to eliminate as much as i can, but do you think its wise to put the isolator on the incoming line so all the distributed coax lines are filtered or just on the particular line that has the humbars?

If the problem is, in fact, that box, it would be better to isolate that box from the rest of the system.
 

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Lets back up a step -


There are actually LOTS of things that cause interference, degraded quality, diagonal or horizontal bars in a picture. Interference from TV IF frequencies (mostly on older tube TVs), interference from "leak-ins" - FM radio being one of the worst - usually traceable back to bad connections, reflections due to improper terminations, cheap amplifiers you buy at the local dry goods store with either poor signal to noise ratios or bad grounding in themselves etc... Each has it's own way to track down the issue, and frankly I've not seen a great source for this information (perhaps someone should write a book)...


And hum - if that is what it is - (sounds like you got that nailed but a disclaimer is always a good idea), is almost always caused by something other than what seems obvious. I had a long conversation with the head Comcast trainer in my area the other day on this very topic - they are upgrading their systems all over to accept the new VOIP systems, and grounding is one of the biggest issues. The #1 most common cause they have found in the field? TVs and A/V receivers that actually are returning some current through the COAX instead of via the power ground. i.e. if ANY equipment in your home finds the coax the easiest path back to ground you get hum. He said it was frequently a trial and error of grounding each coax jack/connection to see where the hum changes (grounding a receiver, connecting power ground to coax outside metal etc...

But the interesting part (and perhaps applicable to your other question) is they find a lot of grounding issues with distributed amplifiers - moral of the story - always do all of your amplification in one place - all plugged into the same outlet - and buy good amplifiers. If you pay less than $30 for a drop amp you will probably regret it.


As for stacking, generally no (EE background) - the other answers in this thread are correct and here is why. Amps have two things you need to worry about in-out amplification and Signal/Noise ratio sometimes expressed as a noise figure. If you amplify a signal you are also amplifying the noise already present on that line by the same ratio - best bet is to always amplify as close to the clean input source to your home as possible. Then either use a drop amp with multiple outputs or split before you amplify different parts of the home - you never want to overload the input to an amp (some can only handle +10dB in and if you amp twice in a row you will overload and distort the signal), and if you have already amplified the noise and amplify it again, you could very well put the noise well into a range that a TV can no longer discriminate.


Tru-spec (actually pico macom I think) has some really great drop amps, some with 4 or 8 outputs already conditioned and individually amplified you might want to take a look at.


Good Luck


DF
 
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