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Old 24-Jan-2011, 5:26 PM   #6
Join Date: Dec 2009
Posts: 632
Originally Posted by deacon-bart View Post
what is the DC passthru I see on the diplexers? I notice this allows signal on one input but I loose it on the other side without DC passthru.
On diplexors, the "low" frequency side usually passes all signals through from the cutoff frequency down to zero Hz. This includes allowing DC power to pass through this side (a simple voltage bias). In some circumstances, this is important because some devices (e.g., the LNB in a satellite dish, a mast-mounted OTA pre-amp, etc.) take their power from the coax directly. That is, there is sometimes a power supply indoors that puts DC power on the coax so that the upstream device can be powered without requiring an electrical outlet on the roof (it also keeps the "noisy" power supply electronics far away from things like the amplifier circuits).

If power is being sent up the coax, then you need to know whether or not it will make it past any diplexors/splitters that are in between the supply point and the device needing the power. You also want to make sure you're not sending power to devices that are not expecting any.
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