21-06-2017, 05:42 PM
(21-06-2017, 10:08 AM)Terry Wrote: There seems to have been a fair bit of opposition to my explanation, including my last comment regarding the differences between transmitting and receiving antennae (which totally ignores the fact that, in this case, the 'transmitter' has an output frequency range of 85 - 750MHz!) so, do we have "a better brain than mine" to bail me out here ...?
Warning I do wander off subject!
About 55 years ago when I was studying antennas I made a one tube 400 Mhz transmitter and a simple receiver which feed a vacuum tube voltmeter (VTVM). The course material included a graph paper which was a series of circles and radial lines representing the compass direction. I built different types antennas starting with a simple dipole. Placing the antenna on the graph paper and rotating it in 5 degree step and recording the VTVM reading gave the data need to produce a radiation pattern for each antenna design. The course material said the radiation pattern and the receive pattern would be the same. Once the chart was plotted I would change the antenna on the transmitter and the receiver and retest to prove they were the same. I was using a yagi and a dipole and it made no difference if the yagi was transmitting or receiving. So yes you are correct in what you said.
(The transmission line were bare solid copper wire so I could measure the standing waves on it too. The good old days!)
BUT...
In the computer age we have more to look at than just transmission lines and sending and receiving over them. Even the simple fire alarm system will have diagnostics build into them to "prove" system integrity. The computer will look for the terminator and when it is not found sound an alarm declaring a system problem. The terminator is at the last alarm on the loop and the test proves no wires are broken between the computer and the end of the loop.
The industrial computer (Modicon) will check for the terminator on both ends of the cable. I had one up and running with no terminators. The engineer and designer came in and put a terminator one one end the Modicon still functioned. They put a terminator on the other end and it failed. I put a resistor acoss the first terminator and it came back to life. Even after explaining to them that the first terminator was open and proving it by putting a resistor across it they insisted on switching the terminators from one end to the other. Modicon wants one at each end or none at all.
I said all that to lead to this one possibility. Maybe the TV company charges but the connection and they pole the system to see how many sets are connected, how many to bill for.
follow the money.
When my brother-in-law passed I called and told them he now longer required their services and they wanted all the cards from the boxes. They said they would continue billing until they received them. I was tempted to let it go and see how they collected from a dead man but I complied with their request and returned their property to them.
I do ramble but it could be food for thought.
73
