Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site brl-tgr.ARPA Path: utzoo!linus!philabs!cmcl2!seismo!brl-tgr!tgr!d3unix!jhs@mitre-bedford.ARPA From: jhs@mitre-bedford.ARPA Newsgroups: net.ham-radio Subject: Re: RF Probes Message-ID: <1673@brl-tgr.ARPA> Date: Mon, 23-Sep-85 16:30:06 EDT Article-I.D.: brl-tgr.1673 Posted: Mon Sep 23 16:30:06 1985 Date-Received: Wed, 25-Sep-85 11:24:15 EDT Sender: news@brl-tgr.ARPA Lines: 15 People trying to make voltage dividers etc might make something of the following observation: If you have an R shunted with a C as input impedance of some device like a meter or amplifier, you can make it into a voltage divider / lowpass filter by putting an R shunted by an L in series with the original RC combination. If the R values are equal then choose L so that sqrt(L/C) = R, and the whole thing will look like EXACTLY R at ALL frequencies as seen from the input, while giving a 2:1 voltage division ratio at frequencies well below cutoff. Often the cutoff frequency comes out acceptable. Cutoff frequency is of course 1/(2*pi*sqrt(LC)). The other approach is the capacitive compensation approach, which avoids the cutoff problem but which presents a capacitive input impedance. 73, de W3IKG Brought to you by Super Global Mega Corp .com