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PA2AGA > HDDIG 26.07.00 02:42l 176 Lines 7337 Bytes #-9302 (0) @ EU
BID : HD_2000_200G
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Subj: HamDigitalDigest 2000/200G
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Sent: 000725/1806 @:PI8HGL.#ZH1.NLD.EU #:64457 $:HD_2000_200G
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Tue, 25 Jul 00 17:08:56 MET
Message-Id: <hd_2000_200G>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
>> cost much more.
>I think it would have cost considerably more. You can't simply pass
>audio through and opto-isolator. It would require proper biasing and
>audio amps. Just another place to create distortion and ruin the IMD
>on the receive and transmit signals. Isolation transformers are a much
>more reasonable approach.
I agree with that. Transformers somehow seem to have a bad name, but
a transformer that handles 5 kV between primary and secundary and has
very good audio characteristics can be found in any telephone modem.
These are mass-produced items costing very little.
Optocouplers are tricky devices that are not easy to use in demanding
applications (linearity, fast switching). Avoid them when you can use
other methods.
Rob
--
+----------------------------------+--------------------------------------+
| Rob Janssen pe1chl@amsat.org | WWW: http://www.knoware.nl/users/rob |
| AMPRnet: rob@pe1chl.ampr.org | AX.25 BBS: PE1CHL@PI8WNO.#UTR.NLD.EU |
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Date: Tue, 25 Jul 2000 09:10:19 GMT
From: nomail@rob.knoware.nl (Rob Janssen)
Subject: RigBlaster
George , W5YR <w5yr@att.net> wrote:
>An interesting thought is that despite the optocoupler for the PTT line
>and the isolation transformer in the transmit audio line to the radio mic
>input, the computer chassis is tied directly to a-c protective ground
>through the "green" wire in its power cable, as is the radio. Thus, the
>two chasses are connected despite the presence of the optocoupler and the
>transformer.
It looks like you do not understand what a ground loop is...
A ground loop is a circular connection of ground between two or more
points. In this situation: both transceiver and computer have their ground
connected to the safety ground of the mains, and their grounds are also
connected together via a signal cable.
Now you have a loop connecting three points. Any magnetic field spanned by
this loop will induce current in it, and this current my get converted into
voltage when there are some non-ideal connections involved.
This voltage is then added to the modulation signal (in this case).
Putting isolation transformers somewhere in this loop (can be in the signal
path, can be in the mains connection) you break the loop.
OF COURSE the two boxes are still connected (unless you have at least two
points of insulation), but the point is that no CURRENT can flow through
the loop anymore, and thus no voltage is introduced anymore.
>Some folks have had to resort to two-prong a-c adapters to
>break up this common connection when operating PSK31 and other digital
>modes involving the computer.
Those guys did not solve it in a safe and sound way.
>The situation is even more interesting when you consider a
>computer-controlled radio like my Kachina. There the RS232 cable to the
>radio runs a wire from computer chassis ground to radio chassis ground as
>the common for computer/radio communications. Thus, there is yet another
>conductor circumventing the optocoupler and transformer "isolation."
That is why controlling a radio using RS232 is not a very clever thing
to do. They should have at least isolated the RS232 interface from the
chassis (using optocouplers and a DC/DC converter), simpler would be to
use an interface that has isolation by design. Ethernet, optical fibre,
IRDA, you name it.
>I don't know about you folks, but my interface consists of two shielded
>audio cables from Radio Shack. No ground loops, no feedback, no hum.
You DO have ground loops, probably two, but you are not hit by them now.
Remember: the problem of a ground loop is that a current is introduced
by a magnetic field. This current will be small when there is little
magnetic field spanning the loop. This may be accomplished by making
the surface of the loop as small as possible (e.g. by tying cables together
that run to the same node in the loop. tywrap the RS232 and signal cables
between computer and rig togheter, tywrap the mains cables from rig and
computer together). Unfortunately this method is often in conflict with
another rule: try to keep cables from the computer as far away from other
cables to reduce noise and birdies.
Also, a small voltage introduced by the groundloop current will be more
harmful when the signal level of the wanted signal is low. That is why
it is a bad idea to connect a digital box to the MICROPHONE connector
of a transceiver. Microphone signals have a very low level, so there
is a lot of amplification behind that connector. Use a LINE-level input
and the problems will be much less or will even be absent. This is what
you may be doing with your Kachina.
But it is no guarantee. Look (in other newsgroups) at the number of
people attempting to connect their computer sound card to their HIFI
system these days. They of course have the same problems, especially
when the HIFI system is connected to an antenna or cable. They also
want the hum to be even less than amateurs would live with, so even with
LINE-level signals they need isolation.
Rob
--
+----------------------------------+--------------------------------------+
| Rob Janssen pe1chl@amsat.org | WWW: http://www.knoware.nl/users/rob |
| AMPRnet: rob@pe1chl.ampr.org | AX.25 BBS: PE1CHL@PI8WNO.#UTR.NLD.EU |
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Date: 25 Jul 2000 02:58:20 GMT
From: kt4ht@aol.com (Kt4ht)
Subject: Rigblaster with Yaesu FT-840 Help Needed
I have a Yaesu FT-840 that I am trying to use the Rigblaster with. Using
Digipan, I have not been able to get the automatic keying to work. When I plug
in both the serial cable and audio in from the computer to the Rigblaster, the
automatic keying does not work. With the audio in disconnected, the automatic
keying works fine, but of course, there is no transmit audio.
The jumpers are set as per the manual for Yaesu rigs and all michrophone
functions work correctly. I can send PSK31 if I key the rig manually.
Any help would be appreciated.
Mike, KT4HT
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Date: Tue, 25 Jul 2000 02:51:07 GMT
From: jdouglas@timewave.com (John Douglas)
Subject: RTTY & Digital HF
Hello Del,
try 45 baud.
See <http://www.timewave.com> for the news on PK-232 upgrades and options.
73
John N0ISL
Timewave technology
See <http://www.timewave.com> for the latest in DSP-599zx upgrades.
In article <3979b16c.684767@news.usol.com>, dmccord@usol.com (Delbert McCord)
wrote:
>I have gotten the bug to play on HF Digital so I dug out my OLD PK232
>from the garage and low and behold it still works. I find the I do not
>reconise all the digital stuff I am hearing out there.
>
>1) Are there still RTTY nets that happen at a regular time daily,
>weekly or a freq there I will usualy find RTTY?
>
>2) I found what I thought was a RTTY station and I tried and tried
>(with a very good signal) but I think I have the baud incorrect. When
>I was in it before (On VHF) we usualy used 60 Word per min (45 Baud)
To be continued in digest: hd_2000_200H
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