|
August 2000 Meeting ReviewTransmission Line Theory 101Fred Gotwald, PE Question: To maximum power transfer from generator to load via a transmission line, what should you remember? Answer: Don't step on the cable! Stephen Lampen of Belden discussed how to minimize return loss (and therefore power transfer) by maintaining the characteristic impedance of a coax. 
Assuming the dielectric is uniform and constant, the impedance is governed by the ratio of the radii of the outer and inner conductors. Any deformation (stepping on the cable, tie-wraps too tight, putting heavy equipment on the cable) will cause local variation to the impedance and lead to lower return loss. Also, remember to vary the distance between tie-wraps to avoid periodicity and a spectrum which looks like a picket fence. Another note - be wary of feedthroughs and barrels. You might be very lucky to get 75 ohms at 2 GHz with them. Both Mike Curran and Scott Stinson asked that Belden mark their video cables with ascending distance (like data cables), so you can tell how much cable is left on the reel. As the full moon was rising, Bob Behrent of Bomar had gremlins invade his computer. He managed to fight them off and describe the SD and HD connector products. A big thank-you goes out to Bruce, Jim and the crew at Western Radio for hosting the event and for the extremely tasty treats they provided. Chapter business included a reminder that next month is elections! Please consider running for office. |
||