View Full Version : Distribution Amplifiers
01-11-2006, 09:50 AM
Recently bought standard amplifier for my cable input. It immediately increased my signal for analog and digital broadcasts. However, it knocked out my cable internet and high definition channels. When I disconnect the amp, both come back immediately. The only amp I've seen on the internet which might work is Channel Plus' DA550BID, which runs anywhere from $200 to $300. Do I have any other choices? What exactly should I be looking for? Thanks for the help.
01-11-2006, 10:40 AM
Here's what I'd do. Contact your cable provider and have them check your drop for proper signal levels. If they say it's fine then you have bad/damaged coax inside your house, and/or bad connections, and/or too many splitters. Solution 1.. disconnect the drops not used and remove the splitters involved. For every 2-way split you loose 1/2 your signal power level(3db). If you insist on having a drop in every room and want to have all those drops connected all the time,(the reason you have all the splitters), then ask your cable provider what frequency band your hi-speed service is transmitted at and then you will know what to get for an amplifier.
The problem is that most RF amplifiers have a high pass filter at around 45-50 MHz which is the start of video for NTSC (North American TV standard). Your cable modem uses the band below that as the return path.
You need find an amplifier that supports a return path from 5-45 MHz.
> Recently bought standard amplifier for my
> cable input. It immediately increased my
> signal for analog and digital broadcasts.
> However, it knocked out my cable internet
> and high definition channels. When I
> disconnect the amp, both come back
> immediately. The only amp I've seen on the
> internet which might work is Channel Plus'
> DA550BID, which runs anywhere from $200 to
> $300. Do I have any other choices? What
> exactly should I be looking for? Thanks for
> the help.
> Gerry HIggins
Lot of good info going here, but do you really need a 55db rf amp. Thats mighty huge.
Your cable drop at the head end should be 0 to +4db before you go out in to spliters then the house.
Most tv's and/or cable boxes can deal with -10db inputs and still perform well.
Ok this is off the top too.
RG59 cable has about 7-8db loss per 100ft @ 500mhz.
RG6 cable has about 5db loss per 100ft @ 500mhz.
RG6 quad has about 3-4db loss per 100ft @ 500mhz.
2 way 3.5db loss
4 way 7db loss
8 way 10.5db loss
16 way 14db loss
give or take a little...(you could add connector losses to if you like. Rule of thumb is .5db loss per connector, and .5db for barrles)
Best idea to do is split the feed into the house with a 2way, one to the cable modem the other to your amp.
Add up the losses for your cable runs and what ever you need for a spliter.
Once you figured out what the max losses are on the longest run then get an amp that is close to that number and maybe a little extra.
Most tv/cable boxes can take a +10db singal without overloading the front end.
Example...(in a perfect world)
Cable coming in is at +3db, hits the first spliter leaving you at 0 db. Cable modem on one side at 0db will be very happy.
Now say there are 8 drops of RG6 quad, longest run is 100ft from the head end. So add cable loss to the spliter loss (4db+10.5db=14.5db loss).
Ok, we have 0db to work with and the worst run is -14.5db. So you would need a amp that will output 20-22db. That gives you +5.5 to +7.5db of head room to play with(plenty).
Remember to always use 75 ohm end of line terminators. Even on the spliter if there is an unused port. This keeps the system balanced.
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