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PA2AGA > HDDIG 26.07.00 02:08l 158 Lines 7311 Bytes #-9303 (0) @ EU
BID : HD_2000_200D
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Subj: HamDigitalDigest 2000/200D
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Sent: 000725/1803 @:PI8HGL.#ZH1.NLD.EU #:64454 $:HD_2000_200D
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Tue, 25 Jul 00 17:08:48 MET
Message-Id: <hd_2000_200D>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
> NOT ONLY on the PTT keying line BUT ALSO on BOTH of
> the audio lines to and from the sound card. It would have not
> 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.
By the way, a transformer can break up a ground loop even if there are
other ground connections between the computer and the rig. If properly
connected, the transformer will prevent the ground currents from
flowing through the shield of the audio line where it causes the most
problem. Actually, even if you isolate the receive line, the transmit
line and the PTT circuit you will (I hope) still have a common ground
via the power line safety ground. The rig and the computer are never
totally isolated - if they are they you could have a shock hazard.
------------------------------
Date: Mon, 24 Jul 2000 19:48:39 -0400
From: "Rob" <Pse@NoEmail.Com>
Subject: RigBlaster
Yes, if you use opto-isolators on the audio lines to and from the sound card
you will need to also use op amps and the proper biasing circuitry. Such a
circuit is very easy to build and design. G3VFP Has recently designed and
built such a circuit. But I don't think that such a circuit would
considerably add to the cost of a RigBlaster. (I am not talking about
selling price but cost). The cost of the circuit board would be about the
same and the extra cost for the additional parts would not be very much. If
there was any significant additional cost, it would likely lie in the extra
cost in building such a unit. Yes, the circuit must be designed properly
but that is part of what you are paying for when you buy a commercial
product.
The REAL advantage of using opto isolators is to better protect your
computer's sound card from any dangerous voltages coming from the rig or
vice versa due to malfunctions or improper installation.
Yes, I agree that there is always a ground connection between the computer
and rig via the AC ground line. Complete isolation is not possible nor
desirable. But the real goal of any sound card interface is to break up the
ground loops on BOTH of the AUDIO LINES to and from the sound card and on
the PTT line. Audio isolation transformers do a good job at breaking up the
ground loops on the audio lines.
But some HAM's defeat the purpose of using audio isolation transformers in
the first place by using a simple one transistor, one diode and one resistor
circuit to key the PTT line of the rig. Such a simple one transistor etc
PTT keying circuit provides a direct ground connection between the rig and
computer which can cause havoc when transmitting. It is best that any
ground loop on the PTT keying circuit be broken up by using a relay or opto
isolator. I think RigBlaster uses an opto isolator on the PTT keying
circuit.
You mention that RigBlaster does NOT offer ANY isolation on the receive
audio line. That is too bad. If the Receive line is connected directly
between the rig and computer, RigBlaster may not solve the problem created
by ground loops. In some cases, ground loops on BOTH the Receive and
Transmit audio lines NEED to be broken up using audio isolation transformers
(or opto-isolators). It sounds like RigBlaster only does half the job on
the audio lines.
In my view, the ideal interface would consist on two audio isolation
transformers and variable POT's on the audio lines to and from the computer
and a simple opto isolator PTT keying circuit consisting of one
opto-isolator, two diodes and one resistor. If you don't have a packet or
accessory jack on your rig and must use your rig's mic jack, then you may
want to throw in a switch. For circuit diagrams see
http://www.qsl.net/wm2u/interface.html and
http://www.w5bbr.com/soundbd.html. LESS THAN TEN PARTS ARE TYPICALLY
NEEDED.
In my view, such a circuit is NO more complicated than a HAMCOMM interface
and should have a similar selling price. (e.g the selling price for a
BayPac Hamcomm style interface is $49.95. I don't think it will be long
before someone starts selling a sound card interface for somewhere between
$40 and $50 US that break up the ground loops ON BOTH of the audio lines to
and from the sound card AND on the PTT line).
73's
Rob
"Bob Lewis" <rlewis@staffnet.com> wrote in message
news:XI3f5.27$1N5.350@newsfeed.slurp.net...
> > I think you will find that RigBlaster does NOT use a power
> > transformer to power the 4N33 opto-isolator.
>
> It does require an external 12 VDC power source to operate the
> opto-isolator and the relays though. They provide a wall wart.
>
> > The transformers in RigBlaster are more likely audio isolation
> > transformers used to break up any ground loops on the
> > audio lines to and from the sound card.
>
> RigBlaster handles ONLY the PTT and Tx audio lines. Receive audio does
> not pass thru the RigBlaster. Transmit audio does pass through an
> isolation transformer.
>
> > Personally, I would have liked to have seen opto-isolators used
> > NOT ONLY on the PTT keying line BUT ALSO on BOTH of
> > the audio lines to and from the sound card. It would have not
> > 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.
>
> By the way, a transformer can break up a ground loop even if there are
> other ground connections between the computer and the rig. If properly
> connected, the transformer will prevent the ground currents from
> flowing through the shield of the audio line where it causes the most
> problem. Actually, even if you isolate the receive line, the transmit
> line and the PTT circuit you will (I hope) still have a common ground
> via the power line safety ground. The rig and the computer are never
> totally isolated - if they are they you could have a shock hazard.
>
>
>
------------------------------
Date: Tue, 25 Jul 2000 00:44:52 GMT
From: "George , W5YR" <w5yr@att.net>
Subject: RigBlaster
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. 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.
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
To be continued in digest: hd_2000_200E
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