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Message-ID: <0BF291DC12234E64A438CBF3CEDDB776@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <201101111216460781.5C69093B@smtp2.numeo.fr>
In-Reply-To: <201101111216460781.5C69093B@smtp2.numeo.fr>
Date: Tue, 11 Jan 2011 13:47:09 -0000
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Subject: LF: Re: RF ammeter question
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Dear John, LF Group,

The 1N4007 and similar HV rectifiers have a notoriously slow recovery - it 
is sometimes seen in amateur literature used as a PIN diode for this reason. 
So one could expect problems using it as an RF rectifier. I have made a 
number of versions of this ammeter circuit, using various small switching 
diodes without problems at 136k and 500k. The Schottky rectifier diodes you 
mentioned should have no problem with switching speed. They have quite high 
capacitance, but I guess this probably won't be a problem in this relatively 
low impedance circuit.

Cheers, Jim Moritz
73 de M0BMU

----- Original Message ----- 
From: "John RABSON" <john.rabson@numeo.fr>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, January 11, 2011 11:16 AM
Subject: LF: RF ammeter question


LF,

I have built the fullwave rectified version of the design shown on page 
10.33 of the RSGB Handbook 10th edition.  It reads correctly at 25kHz but 
only show 1/3 of the correct value at 136.

Not having any 1N4148 diodes I used 1N4007s.  Might this be the cause of the 
problem?

73
John F5VLF