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Electronics => Beginners => Topic started by: w2aew on August 04, 2015, 12:22:43 am

Title: New video: Visualizing RF Standing Waves on mis-terminated transmission lines
Post by: w2aew on August 04, 2015, 12:22:43 am
This video shows how standing waves are created on transmission lines from the addition of the forward (transmitted) wave and the reflected wave resulting from unmatched termination impedance.

https://www.youtube.com/watch?v=M1PgCOTDjvI (https://www.youtube.com/watch?v=M1PgCOTDjvI)
Title: Re: New video: Visualizing RF Standing Waves on mis-terminated transmission lines
Post by: KD0CAC John on August 04, 2015, 03:08:32 am
Another good video , thanks again .
I wandered a while back that if measuring directly on feedline , that I should measure in multiple places , not just one spot .
Title: Re: New video: Visualizing RF Standing Waves on mis-terminated transmission lines
Post by: w2aew on August 05, 2015, 01:04:08 pm
Quote from: KD0CAC John on August 04, 2015, 03:08:32 am
Another good video , thanks again .
I wandered a while back that if measuring directly on feedline , that I should measure in multiple places , not just one spot .

It all depends on the length of the line with respect to the wavelength of the signal being transmitted.

This also explains why - if you're having trouble adjusting your transmatch/tuner on a given band, that it can often help to add/remove some line between the tuner and antenna - because the impedance looking into a mismatched line will vary with line length (at a given operating frequency).  Adding or removing a bit of line can move the impedance off of a difficult-to-tune impedance extreme (node or anti-node).
Title: Re: New video: Visualizing RF Standing Waves on mis-terminated transmission lines
Post by: ElectroIrradiator on August 05, 2015, 01:47:37 pm
That little experiment brings back memories. :)

Long time ago I literally measured the wavelength of an abused 2K25 X-band klystron by noting the distance between troughs in the standing wave reflected from a flat metallic surface, sitting perpendicular to the incident radiation. The metallic surface was a piece of polished PCB, and the slide it was riding on incorporated a micrometer. This was done because the 2K25 normally won't tune up into the 10GHz amateur band, but ... with a bit of help from a persuasion device...  ;)