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Re: [Amps] Sampling RF at input and output of an amplifier

To: "Pete Smith N4ZR" <n4zr@contesting.com>, <amps@contesting.com>
Subject: Re: [Amps] Sampling RF at input and output of an amplifier
From: "Paul Christensen" <w9ac@arrl.net>
Date: Thu, 16 Jan 2014 07:45:07 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>
I want to use an oscilloscope to view the relative timing of the relays in my homebrew QSK system, and would like to be able to sample the RF as simply as possible. Absolute amplitude isn't important, but timing is. What is the minimalist approach?

Pete,

For quick QSK timing measurements, I often inductively couple the sample point to the scope. You can use a short coaxial jumper with BNC connectors on both ends and connect one end to the scope, the other end to a BNC-to-banana adapter. Then, take an alligator clip test lead and wrap it in close proximity to the sample point. The lead ends are connected across the adapter.

Unless you're sampling low power, there's often enough coaxial leakage to just wrap the lead around the coaxial jumper. Then, adjust the scope's vertical amplifier to fill the display. Generally, I can get good display quality without much noise. You may need to experiment with more or less turns around the line.

Paul, W9AC
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