Words of Wisdom from the Past

...about transmission lines. This article, by an unknown author but edited by Doug VE3CWO (Now VE3VS) provides some pointers on understanding transmission lines. It has been scanned from the January 1974 edition of the Splatter and passed through optical character recognition for publication here. You can see the entire newsletter scanned from an original on the YRARC web site. Thanks to Bob VE3WY and Rob VE3RQB for passing this along.

HELPFUL FACTS ABOUT TRANSMISSION LINES

While the following statements are elementary to many old-time amateurs, it is hoped that these condensed and simplified points will be of some help to the newcomer in obtaining better performance from his station.

1. To deliver maximum power with lowest losses, a transmission line must be terminated in a resistance equal to the characteristic impedance of the line.
   
2. A correctly terminated transmission line of any length will, from the sending end (transmitter), appear as an impedance equal to the characteristic impedance of the line.
   
3. A correctly terminated and balanced line has essentially no radiation from the line.
   
4. A correctly terminated line has the most power absorbed by its termination (load); hence, none is reflected and its V.S.W.R. is unity.
   
5. If a line must be pruned or adjusted to a critical length, it is not terminated properly.
   
6. No matching device at the sending end (transmitter) can reduce the V.S.W.R. on a line which is improperly terminated.
   
7. An improperly terminated or unbalanced transmission line will:
   
   1. Reduce power capacity of T.V.I. filters.
      
   2. Distort radiation and polarization patterns of the antenna.
      
   3. Induce power losses in nearby objects or buildings.
      
   4. Increase B.C.I. and T.V.I. problems.
      
   5. Not absorb or transfer maximum power from many types of transmitters.
      
8. Improperly terminated transmitter lines, when used for receiving, may cause reduction in apparent receiver sensitivity due to losses because of mismatch between antenna and line.
   
9. To obtain maximum transfer of power between any two networks, the impedances must be equal, or must be equalized by a matching network or transformer.