Sony DRD GX300 is old school, low resolution only, that can only record the old NTSC Analog RF signals, found only on some cable system's Analog Tier and a limited number of low power, limited audience OTA stations and repeaters...which are being phased out "soon" All of the major networks have transitioned to DTV On-Air (ATSC) signals which will NOT be recognized by the GX300.
If you want to still use the GX300, you COULD pick up an inexpensive new or used low-rez CECB (Coupon Eligible Converter Box), which can output NTSC on RF Ch3/4 or Composite Video (Yellow/Red/White). You'll also have to manually select the channel via CECB controls you want to record on GX300.
What you SHOULD do is consider purchasing an OTA ATSC HD Recorder, which can output 720p or 1080i (sometimes 1080p) to the DLP via either Component Video (Red/Blue/Green) Interface or DVI (HDMI to DVI cable may be required) or HDMI-HDMI cable if DLP is so equipped. TiVo HD DVR is one of the better alternatives (monthly subscription or higher "lifetime subscription" purchase price option). Be advised that DVD Recorders with built-in OTA ATSC Tuners record in a format that has reduced resolution, which is then upconverted to 720p or 1080i (and maybe 1080p) for output via Component Video and HDMI Interfaces. See HD OTA Recorder Threads for info on these and other options: