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EB2DVY > PSK31 09.12.99 06:21l 127 Lines 4289 Bytes #-9729 (0) @ WW.SYD.NSW.
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To : PSK31@WW.SYD.NSW.AUS.OC
De: Psk31 Digest <owner-psk31@bipt106.bi.ehu.es>
Para: <psk31-digest@bipt106.bi.ehu.es>
Asunto: Psk31 Digest V1 #246
Fecha: martes 30 de noviembre de 1999 4:37
Psk31 Digest Tuesday, November 30 1999 Volume 01 : Number 246
In this issue:
RE: [psk31] Ground loops
RE: [psk31] Ground loops
Re: [psk31] optoisolator interface
See the end of the digest for information about psk31-digest
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Date: Mon, 29 Nov 1999 12:05:56 -0000
From: "Adrian Rawlings" <adrian@euroneta.com>
Subject: RE: [psk31] Ground loops
Transformers are one solution. The problem is that they, themselves, can
pick up hum.
I was wondering about using an Op Amp pre-amp with high-Z differential
inputs. The reasoning behind this is that the hum would be a common mode
signal and would not, within certain limits, get through.
Has anyone been down this road before? Am I missing something?
Adrian
(UK callsign = m0ans)
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Date: Mon, 29 Nov 1999 09:58:02 -0500
From: Charles Greene <cgreene@loa.com>
Subject: RE: [psk31] Ground loops
At 12:05 PM 11/29/99 +0000, Adrian Rawlings wrote:
>Transformers are one solution. The problem is that they, themselves, can
>pick up hum.
>
>I was wondering about using an Op Amp pre-amp with high-Z differential
>inputs. The reasoning behind this is that the hum would be a common mode
>signal and would not, within certain limits, get through.
>
>Has anyone been down this road before? Am I missing something?
Yes, works fine. Some commercial interfaces use an op-amp
instead of a transformer.
____________
Try PSK31. Check: http://aintel.bi.ehu.es/psk31.html
and May 99 QST. K2 S/N 462.
Chas, W1CG
Rhode Island TCPIP Address Coordinator
w1cg@arrl.net
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Date: Mon, 29 Nov 1999 13:39:29 -0600
From: John Chamberlain <chamber@cord.org>
Subject: Re: [psk31] optoisolator interface
On Sun, 28 Nov 1999 19:57:50 "emi2" <emi2@worldnet.fr> wrote:
> ...there is also the possibility to isolate the PTT switch...with the
> help of an optoisolator connected to the serial port...
<snipped>
> ...Connect then pin 5 of the optoisolator to the PTT input of your
> transceiver...A diode 1N4001 to avoid damage from spikes is
> recommended. Cathode to pin 5 and anode to pin 5 of the optoisolator.
> That's it, your RX/TX is now perfectly isolated from the computer.
Ezio,
Optoisolators are neat little devices.
However, if I understand correctly, you are connecting the ground (Serial
pin 5) from the computer to the optoisolator's pin 5 which is also
connected to the radio's PTT. So, in fact the radio and the computer are
NOT isolated as you say, but connected through a diode. But then, maybe I
have misunderstood your good attempt to describe the circuit (in English,
too! :-). Perhaps "a picture (schematic) would be worth a thousand words,"
as we say in America.
73 de AC5CV
John Chamberlain (AC5CV@arrl.org)
Waco, TX EM11jm
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End of Psk31 Digest V1 #246
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