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From: "John Jardine"
Subject: Re: RF voltmeters
Date: Tue, 24 Dec 2002 15:29:46 -0000
NNTP-Posting-Date: 24 Dec 2002 15:16:39 GMT
X-Newsreader: Microsoft Outlook Express 5.00.2615.200
Paul Burridge wrote in message
> Given the difficulty I experienced measuring RF voltage levels using a
> 'scope (given the loading effect of the probe and/or scope itself)
> I've been pondering making up an RF probe for my DVM in the hope of
> getting more accurate readings of RF voltages. Does anyone have a view
> on whether this option would prove less troublesome than using a
> 'scope alone?
> "What is now proved was once only imagin'd"
> - William Blake, 1793
A sharp probe, small cap, 1N4148 diode and a 1Mohm resistor and 2" of ground
lead with croc clip can easily give a near flat response to 150MHz. Crappy
construction makes little effect on the performance. Biggest problem is
using too long a ground lead. Don't expect perfectly linear readings as the
diode starts losing it below about 1/2 volt.
Gets a bit better if you go for a voltage doubler using two diodes and 2
caps but that's moving into the 'designing a fancy probe' arena ;-)
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