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PA2AGA > HDDIG 08.08.00 00:42l 155 Lines 6548 Bytes #999 (0) @ EU
BID : HD_2000_205E
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Subj: HamDigitalDigest 2000/205E
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Sent: 000807/2214Z @:PI8HGL.#ZH1.NLD.EU #:3173 [Den Haag] FBB $:HD_2000_205E
From: PA2AGA@PI8HGL.#ZH1.NLD.EU
To : HDDIG@EU
Date: Sun, 30 Jul 00 14:17:46 MET
Message-Id: <hd_2000_205E>
From: pa2aga@pe1mvx.ampr.org
To: hd_broadcast@pa2aga.ampr.org
X-BBS-Msg-Type: B
G3VFP is now selling a both a kit and a completely assembled sound card
interface USING OPTO ISOLATORS THROUGHOUT (unlike RigBlaster which does NOT
use opto isolators on the audio lines). G3VFP's unit isolates BOTH the
receive and transmit audio lines (unlike RigBlaster which only isolates the
Tx line).
There is even a schematic diagram of the circuit for those who want to build
their own. See his web page -- http://www.users.myisp.co.uk/~vfp/kits.htm
The assembled unit costs around 23 pounds (or 50 dollars or so).
He even sells an assembled unit the isolates the RS-232 line for rig
control.
What did I say?? Someone would sell a less expensive unit for around $50
that provides better isolation than RigBlaster!
Rob
"Rob" <Pse@NoEmail.Com> wrote in message
news:EC4f5.35927$qS3.73276@tor-nn1.netcom.ca...
> 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.
> >
> >
> >
>
>
------------------------------
End of Ham-Digital Digest V2000 #205
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