Although the MOD300 has a built-in combiner (RF IN) you may encounter problems when using a “Masthead” amplifier which is powered remotely up the co-ax, as the MOD300’s internal combiner will not pass this power.
The power for the "Masthead" power supply and amplifier will need to be in line before the RF.IN on the MOD300.
1) Remove all the power to the modulator when connecting or removing cables.
2) Connect a HDMI cable from the DVR / NVR (or other video equipment) to the HD IN of the MOD300.
3) Connect a coax (f-connector) to the RF.OUT port direct to the TV or distributor.
4) Connect a coax (f-connector) for the TV aerial signal to the RF.IN port.
4) Connect the 12V DC power supply to the MOD300, then re-tune the TVs.