Passive TV Repeater

Passive & Active Television Repeaters
By Kevin Custer

I have a situation where a cable tv headend is located about 2.5 miles from one of my ham repeater sites. I knew of a situation where a cable operator needed a way to improve a tv station's signal that was on the other side of my repeater site. The tv station, WHAG in Hagerstown MD, inquired about a way to produce a P5 quality picture at the cable headend. We originally discussed receiving the tv station on frequency at the repeater site and then microwaving it to the cable headend. The signal at the cable headend direct from the station was near non existent, below - 35 dBmV. The signal at my repeater site just two and a half air miles away was + 15 dBmV. The repeater site is located on a mountain at over 2900 feet ground elevation, the elevation at the cable headend was over 500 feet lower and the mountain was blocking the signal from the tv station. I decided to place two back to back yagi's at the repeater site, one pointed to the station and one to the headend. The result was a signal that was non existent now became quite watchable. The signal at the headend was nearly minus 20, on uhf, not a bad picture. I then decided to add some gain to the system. I placed a 550 meg Jerrold JLX line extender in the line between the two antennas. I was able to get away with 35 dB of gain before the system oscillated, so a gain of 20 dB was settled on for stability. This then produced a signal at the headend of nearly 0 and nearly P5 (perfect.) Because the line extender has operational bandwidth in the uhf ham band, the uhf repeater at the site overloads the line extender, so band pass filtering before, and after the line extender was added. Since this device doesn't produce a signal greater than 100 mW it doesn't need to be licensed. Cut antennas were used to allow maximum gain on channel and minimum adjacent response.

In this scenario, we were able to produce a good picture with no amplifier. The added amplifier allows a near perfect picture to be rebroadcast over the catv system. Others using outside antennas also benefit. Because of this situation, the tv station agreed to pay my electric bill and has agreed to place a standby generator at the site. This system places NBC 25 WHAG Hagerstown, MD into 20,000 additional homes west of my repeater site in southwestern PA.