20dbcoupler
20 DB Coupler
Using 100:1 (-20 db) couplers to measure RF signals
In his web site Jim Kortge K8IQY talks about his -20 db couplers for RF monitoring. Seems that a good way to sample RF from transmitters for viewing with a spectrum analyzer is with a 100-to-1 transformer or -20 db coupler. Jim shows us how to build these on his web site:
http://www.k8iqy.com/testequipment/-20dbmcoupler
/-20dbmcoupler.htm
And I show you here on my web site how to do it using a cheap (Dollar Store) TV Splitter as the chassis.
This device is a 10:1 broadband transformer that reduces signal level by 20 db or 100:1. If your QRP transmitter output is 20 volts PP (Peak to Peak) across 50 ohms, with this coupler you can sample that signal at 0.2 volts PP.
I used a T37-6 core because that is what I had available. The primary winding is 10 turns. The secondary is 1 turn. The TV Splitter box was drilled in one corner for a bolt and ground lug.
If you make up several coaxial jumper cords with F-type connectors on each end you can use TV splitter chassis boxes for a number of simple circuits, including pads, detectors, splitters, and so forth. I find them handy and inexpensive for these purposes.
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