VHF/UHF Antenna Preamp When Using Diplexor

[mrdbdigital]

My Mom has a standard dual LNB dish with two cables running into the house. We also have a good quality VHF/UHF tv antenna fed into the house over one of the satellite cables using the standard, old DBS/ANT diplexor.

I would like to add a preamp to the television antenna (already have a good quality Winegard preamp on hand) and was wondering if you guys know of any way I could use that on the TV antenna and provide power to it by using the DC on the cable for the sat LNB. The preamp only uses 3-4 Ma of current and the voltage is in the correct range.

Does anyone make a diplexor that passes DC on the TV antenna side? Or, does anyone here have any practical experience using a preamp on a sat diplexed antenna?

She's all SD right now, with no plans to upgrade to HD until next year and I'm trying to avoid digging up the yard and running another cable. (Its about a 75 foot run)

Any ideas would be appreciated.

[samrs]

This will work.

http://pimages.solidsignal.com/pvdp2pp_zoom.gif

http://www.solidsignal.com/prod_display.asp?prod=PVDP2PP

[unc8185]

I have a Winegard GS1100 with a outdoor amplifier. I use a diplexer that passes DC through. Thus, the power for the amplifier comes from the satellite receiver. This works well.

[AntAltMike]

How did you determine that the preamp only uses 3-4 mA? Is that what the preamp power supply's 110 volt input uses? I would expect the preamp to use closer to 100 mA. Fortunately, your receiver's LNB power supply should have enough surplus to supply that. I remember that the early Sony DirecTV receivers had weaker LNB power supplies and some people had trouble powering off-air antenna preamps off those.

Having a preamp in the LNB circuit will shorten the maximum cable length, but were probably talking ranges of maybe 400 feet with just an LNB versus 300 feet with an LNB plus an off air preamp.

[mrdbdigital]

I measured the current draw through the coax with a meter. It was only a few ma.

Thanks for the response, guys. What a great resource this forum is.

Also, as a side note, there are three receivers feeding the LNB through a multiswitch. None of the receivers are the old type. I ordered the suggested dual port power passing diplexer and will be installing it soon.

[AntAltMike]

Winegard's 12 dB gain pre-amp, the HDP-269, draws 60 mA according to its Spec Sheet (http://www.winegard.com/offair/pdf/WC-809%20%20HDP-269.pdf).

While Winegard's spec sheet for its AP Series pre-amps do not give current draw figures, they amplify anywhere from 19dB to 28dB, and so they would draw considerably more, presuming they had something to amplify.

Did you have the pre-amp connected to the antenna when you measured it with your ammeter? With no signal input, the current draw may be negligible. And was the ammeter set for DC rather than AC (though older Winegard preamps did use I think 19 volt AC power supplies).

[mrdbdigital]

As you surmised, I did not have an antenna connected when I measured it. I was also in error on it being a Winegard. The amplifier is a Channel Master amplifier. I can't recall the model number and I also can't find the amp. ( I just moved and measured it before I packed) I think it is a CM 7777 or CM 7778. It was supposed to be one of their higher quality amps.

You are probably correct on the current draw. I remember thinking at the time that it wasn't much current I was measuring. When I find the amp, I'll remeasure it under signal conditions. The manufacturer data indicates the power supply is 18 VDC, so I guess it will be OK on the LNB power, although performance may suffer when the LNB voltage is 13 volts.

[samrs]

Also, as a side note, there are three receivers feeding the LNB through a multiswitch. None of the receivers are the old type. I ordered the suggested dual port power passing diplexer and will be installing it soon.

Damn Cuz, why ya got to with hold information. They make switch's that pass power and have the diplexor built in for not much more.. Sigh.

[AntAltMike]

Also, as a side note, there are three receivers feeding the LNB through a multiswitch. None of the receivers are the old type. I ordered the suggested dual port power passing diplexer and will be installing it soon.

Damn Cuz, why ya got to with hold information. They make switch's that pass power and have the diplexor built in for not much more.. Sigh.

When AVSForums ran a thread on this about five years ago, there were very few multiswitches that passed DC on the off-air antenna input port.

I ran a Channel Master 7775 on a 12 volt supply last year. As I recall, the gain was a few dB less than when I powered it to 18 volts.

[mrdbdigital]

Damn Cuz, why ya got to with hold information. They make switch's that pass power and have the diplexor built in for not much more.. Sigh.

I'm not running the off-air signal through the multiswitch. The house has a separate RF distribution system for the televisions. I am taking the off air signal off the LNB cable right before the multiswitch. I'm just using the LNB cable to get the antenna to the house. The antenna distribution system was in the house long before we got DirecTv.

Also, the whole reason for having the long cable run, which is now buried through countless pine tree roots that have grown in (which makes running new cable a fun job) is to get both the dish and the tv antenna out from under the trees to a clear reception location.