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Discussion Starter · #1 ·
First off, I'm a newbee here at avsforums, although I have been an avid reader here for a while. Information I have found on this great site has allowed me to make informed decisions on my recent purchases of two dtv converter boxes and an 37lg30 hdtv. With this new equipment, I have decided it would be beneficial to split the signal coming from my ariel antenna to use with three televisions. Unfortunately, I'm not sure what the make and model of my antenna is, but it is very old. It uses 300ohm wire and is currently only in use in my family room. I would like to split this 300ohm connection in my attic, run a coax cable in place of the existing 300ohm wire to my living room, run coax wires for two bedrooms to a common wall and then to a tv in each bedroom. The length from the antenna to the attic is about 15 feet, the family room is then about twenty feet. The distance to the common wall is probably another twenty feet, then 8 feet to one tv and 20 to the other. I have tried to find a guide or something of the sort online with no luck. If someone has such a resource, please post a link. My questions are as follows...


I would assume I should use rg6 cable, is this correct?


Should I use one three way splitter, or a two way for the living room/bedrooms then another two way at the common wall?


I have heard people say you lose three decibels with each splitter and this amounts to half your signal, is this true and if not what is the real figure?


Is there signal loss with the length of each cable and if so does this apply to the whole system or only whats on that side of the splitter?


I plan to use wall plates for the two bedrooms, will there be signal loss there?


What type of grounding/fuses should I consider to protect my investment in tvs?


Will I need some sort of a preamp (I'm guessing so, don't have one now) and if so what power?


What other sort of equipment will I need?


Preamp before splitters, correct?


Thanks ahead of time!
 

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You will need an indoor/outdoor matching transformer at the antenna to change it from 300 Ohm twinlead to 75 Ohm coax (RG6).


It would be best to homerun each of the outlets to the attic.


I would use an unbalanced 3-way splitter, and connect the furthest outlet to the 3.5dB leg. Two of the ports are labeled 7 and the third is labeled 3.5.


A preamp is used in cases where the receiving antenna is far from the transmitters. A distribution amplifier is used to compensate for splitter loss in multiple outlet applications. Whether you will need an amplifier will depend on the signal without one. Hook everything up, and if it all looks good you probably won't need one.


A 2-way splitter loses ~3.2-4dB. The higher the frequency, the greater the loss. It also varies slightly between manufacturers.


Your antenna must be grounded. It is required to be be so. Bonded to house ground.


You can find splitters and amplifiers here .
 

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Discussion Starter · #3 ·
Thank you for the reply egnlsn! You mentioned the greater the frequency of the splitter, the greater the loss. Is there a formula to find the loss or will the splitter be rated? Also, I have heard I will need a 900mhz splitter, is this correct? I had asked originally if there is signal loss with the length of the cable and if this only applies to that leg of the splitter or the whole system. I would assume since you said you would connect the highest power output to the farthest tv that there is. Is there a formula/rating to find this or is it guess and check? Also, does it affect the whole system? In the event I do need a distribution amp, are these rated in decibels gain? And how would I decide what power I need? Unfortunately, my antenna was installed without a ground. Actually, our house was ungrounded until we moved in and grounded some outlets to water pipes. Would I just attach a grounding wire to the outside of the splitter, or is there a separate piece of equipment I need to ground my antenna? Just trying to learn as much as possible before I try this.
 

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Quote:
Originally Posted by spiderdan398 /forum/post/15414293


Thank you for the reply egnlsn! You mentioned the greater the frequency of the splitter, the greater the loss. Is there a formula to find the loss or will the splitter be rated? Also, I have heard I will need a 900mhz splitter, is this correct? I had asked originally if there is signal loss with the length of the cable and if this only applies to that leg of the splitter or the whole system. I would assume since you said you would connect the highest power output to the farthest tv that there is. Is there a formula/rating to find this or is it guess and check? Also, does it affect the whole system? In the event I do need a distribution amp, are these rated in decibels gain? And how would I decide what power I need? Unfortunately, my antenna was installed without a ground. Actually, our house was ungrounded until we moved in and grounded some outlets to water pipes. Would I just attach a grounding wire to the outside of the splitter, or is there a separate piece of equipment I need to ground my antenna? Just trying to learn as much as possible before I try this.

You can download specifications for typical CATV splitters here . There is also a worksheet you can use to calculate loss through cable.


Yes, loss through a piece of cable affects only that outlet. The most common gain of a drop amp is 15dB. A good source for CATV materials was previously posted. There you will find a variety of splitters and amplifiers.


The antenna should be grounded before it enters the house.
 

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Discussion Starter · #5 ·
Thank you for your continued help egnlsn. You have been most informative. I have just a few more questions. First off, I believe I need to ground the mast of my antenna, but is there any need for a grounding block with a 300 ohm connection. I don't see how they could even make such a thing for a 300 ohm wire. I suppose I could put one after the transformer, but would I get any benefit? Also, I will be putting this equipment in my attic, so will the heat be an issue? I noticed in one of the data sheets in the link you posted that these splitters were rated up to 60 degrees Celsius. My attic probably gets close to that on a hot summer day, although I haven't measured. I did not see a transformer at the link you posted. Would one from home depot or radio shack be sufficient (at least I think they sell these at home depot)? Lastly, should I get a 900mhz splitter and would I look for a similar rating in an amplifier if I need one? Thanks again!
 

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Quote:
Originally Posted by spiderdan398 /forum/post/15425664


Thank you for your continued help egnlsn. You have been most informative. I have just a few more questions. First off, I believe I need to ground the mast of my antenna, but is there any need for a grounding block with a 300 ohm connection. I don't see how they could even make such a thing for a 300 ohm wire. I suppose I could put one after the transformer, but would I get any benefit? Also, I will be putting this equipment in my attic, so will the heat be an issue? I noticed in one of the data sheets in the link you posted that these splitters were rated up to 60 degrees Celsius. My attic probably gets close to that on a hot summer day, although I haven't measured. I did not see a transformer at the link you posted. Would one from home depot or radio shack be sufficient (at least I think they sell these at home depot)? Lastly, should I get a 900mhz splitter and would I look for a similar rating in an amplifier if I need one? Thanks again!

with 300 ohm cable system an air gap lightning arrestor (outside just before it entered your house) was used for each of the conductors because there is no ground/shield like coax, the conductors are balanced (equal).


with a coax system usually the transformer is placed right on the antenna and the coax started there. a grounding block on the coax right before the point the coax enters your house. your mast ground and this coax grounding block would be connected and a conductor travel the outside of your house to a grounding rod. this grounding rod is also connected to your house electric grounding system. you could have the transformer not on the antenna but before any wires enter the house.
 

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Discussion Starter · #8 ·
Thanks for the replies! I have a few more questions regarding grounding.


If the mast is grounded anyway (which it's not at the moment but I should probably ground it while I'm doing this job), an air gap lightning arrestor would be useless anyway since it seems it would only protect against a direct strike, would it not?


I would still need to ground the shield of the rg6 cable to prevent interference, correct?


I notice that a lot of splitters have a terminal for ground, does this do the same thing as a ground block?


Does the coax cable have to be grounded before it enters your house, or could it be grounded in my attic? I've heard it said before it enters your house but I cant see why it would matter unless for a direct strike, in which case a grounded mast should take care of things, correct?


If I do need a grounding block, is there any reason to ground it and the splitter?
 

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Quote:
Originally Posted by spiderdan398 /forum/post/15435772


Thanks for the replies! I have a few more questions regarding grounding.


If the mast is grounded anyway (which it's not at the moment but I should probably ground it while I'm doing this job), an air gap lightning arrestor would be useless anyway since it seems it would only protect against a direct strike, would it not?


I would still need to ground the shield of the rg6 cable to prevent interference, correct?


I notice that a lot of splitters have a terminal for ground, does this do the same thing as a ground block?


Does the coax cable have to be grounded before it enters your house, or could it be grounded in my attic? I've heard it said before it enters your house but I cant see why it would matter unless for a direct strike, in which case a grounded mast should take care of things, correct?


If I do need a grounding block, is there any reason to ground it and the splitter?

The National Electric Code says the downlead MUST be grounded before it enters the house or within 5 ft of entry. Can't use a water pipe within the house, either. Unless a splitter is UL rated, it is not suitable for use as a groundblock.


In the event of a direct lightning strike, NOTHING will help. Grounding dissipates any static that may otherwise build up on the cable. Incidentally, the NEC specifies that the groundblock is to be bonded to the building's grounding system.


Air gap arrestors are for 300 ohm twinlead.
 

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Discussion Starter · #10 ·
egnlsn, thank you for all the help. You have been very informative. Thank you for your very useful post as well johnpost. I've been to all sorts of home improvement, electronic, and even grocery stores in the past couple days. I got a spool of rg 6q coax cable and compression ends at Lowes. I also bought an outdoor 300ohm to 75 ohm phillips transformer to put directly on the antenna and a 3 way phillips splitter. I'm not sure whether this splitter is balanced or unbalanced because it didn't say and the decibels loss was not listed on each leg. For this reason I believe it is balanced. If this splitter works with out dropping any desirable channels, I will keep it. Otherwise, I will probably order a splitter and amp from the link you provided. I have my doubts in whether things will work without and amp, but I thought it was worth a try. There are some phillips amps at lowes and radio shack has amps, but I'm not sure of their quality. Thanks again to egnlsn and johnpost!
 

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Quote:
Originally Posted by egnlsn /forum/post/15410925


You will need an indoor/outdoor matching transformer at the antenna to change it from 300 Ohm twinlead to 75 Ohm coax (RG6).

Is there any advantage in having 2 matching transformers connected to the antenna and running 2 separate coax cables instead of using a splitter?
 

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Discussion Starter · #12 ·
That's an interesting thought Jonnyboy88. I would guess it would make no difference because it is still essentially splitting the signal between two loads. I suppose it could actually be worse since you're using more wire, but I just don't know for sure. Perhaps egnlsn can give his opinion on this.
 

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Quote:
Originally Posted by Jonnyboy88 /forum/post/15451653


Is there any advantage in having 2 matching transformers connected to the antenna and running 2 separate coax cables instead of using a splitter?

I think the signals developed would be a little weaker. As I recall, there is some elementary engineering proof that an inductive circuit transfers the maximum power when the source impedance and load impedance are equal, but if you use two matching transformers, the load impedance will be just 150 ohms.
 

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Quote:
Originally Posted by AntAltMike /forum/post/15451813


I think the signals developed would be a little weaker. As I recall, there is some elementary engineering proof that an inductive circuit transfers the maximum power when the source impedance and load impedance are equal, but if you use two matching transformers, the load impedance will be just 150 ohms.

What he said.


An impedance mismatch would be the result, thus reducing the power transferred from the antenna to the coax.


Not just that, but you would have twice as many connections and electronics to worry about.
 

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Quote:
Originally Posted by egnlsn /forum/post/15436910


The National Electric Code says the downlead MUST be grounded before it enters the house or within 5 ft of entry. Can't use a water pipe within the house, either.

Actually the NEC says you can use a cold water pipe within 5 feet of where it enters the house, provided it's copper. I may be wrong but I think this was changed in 2002.


Local codes may or may not allow this.


Just went through this process with the building dept., and bonded mine to the cold water pipe. I would've preferred house ground (well, house ground is bonded to the cold water pipe anyway ...) but it wasn't feasible for me.
 
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