14520	2018-01-19 18:13:25	Ashhar Farhan	lecher lines
Message	Date	From	Subject
my baby steps into uhf continue. my elmer arun, vu2oz had built his two meter transmitter that multiplied an 8 Mhz crystal to 146 mhz. this was part of his satellite setup for oscar 6. to tune above 30 mhz, he used lecher lines. i remember the setup as two copper wires stretched about an inch apart on a wooden strip. i also remember some kind of an diode based rf meter. my present interest is to replicate this to tune up past the 70 mhz limit of my spectrum analyzer to build a 435 mhz radio. i intend to use the lecher line coupled to the W7ZOI power meter. Q1. if one was to keep the input and output to 50 ohms impedance, how does one couple to uhf rf input to the lecher lines? how do you couple the 50 ohms output? Q2. is it possible to make the lecher line oscillate? the lecher line is useful, methinks, becuase it is self-calibrating. the wavelength is directly read off the scale next to the transmission line. internet and print literature of amateur radio is sparse on this topic. - f
14521	2018-01-19 18:47:43	Thomas S. Knutsen	Re: lecher lines
Lecher lines is a resonant transmission line. Usualy those I have used are inductivly weak coupled to a resonant circuit, but it should not be hard to do capacitive coupling. Moving a short down the line, you will see a dip for each half wave. Make sure you terminate the far end of the Leicher line, or it will give you all sorts of trouble. Usualy, practical Lecher lines are fairly high impedance, given that a 50 ohm balanced line with 1mm wire would have a spacing of 88µn. A 220ohm line made with 1mm wire should have a spacing of 2.2mm, and terminates with a 220 ohm resistor in the open end that is not coupled. A Leicher line accuracy depends on how accurate you can measure the disstance between the dips. Getting a accuracy of 1% or even less at UHF just requires carefull measuring. The principle of using Leicher wires, and the microwave equivalent of using a weak coupled caviety resonator is outlined in the 1946 MIT radiation labratories series book on microwave measurements. 73 de Thomas LA3PNA. 2018-01-20 3:13 GMT+01:00 Ashhar Farhan farhanbox@gmail.com [emrfd] <emrfd@yahoogroups.com>: my baby steps into uhf continue. my elmer arun, vu2oz had built his two meter transmitter that multiplied an 8 Mhz crystal to 146 mhz. this was part of his satellite setup for oscar 6. to tune above 30 mhz, he used lecher lines. i remember the setup as two copper wires stretched about an inch apart on a wooden strip. i also remember some kind of an diode based rf meter. my present interest is to replicate this to tune up past the 70 mhz limit of my spectrum analyzer to build a 435 mhz radio. i intend to use the lecher line coupled to the W7ZOI power meter. Q1. if one was to keep the input and output to 50 ohms impedance, how does one couple to uhf rf input to the lecher lines? how do you couple the 50 ohms output? Q2. is it possible to make the lecher line oscillate? the lecher line is useful, methinks, becuase it is self-calibrating. the wavelength is directly read off the scale next to the transmission line. internet and print literature of amateur radio is sparse on this topic. - f
14522	2018-01-19 19:35:22	Ashhar Farhan	Re: lecher lines
thomas, shouldnt the impedance dip far below the characteristic impedance at quarter waves? my interest is in using the lecher line as the source and detector with a 50 ohm device under test in the middle. so, the restate, an oscillator made with lecher line as the resonate section, with 50 ohms output. a single pole filter made with lecher line that has 50 ohms input. transmission line theory does say that quarter wave transformers are impedance transformers as well. i am going to try loop coupling (similar to what we use in duplexers) and try getting an oscillator going. - f