Bridging L-R of stereo Line Out for single channel diversity RTTY

[conwell]

I'm wondering if diversity receive might help with RTTY decoding, to
reduce deep fades.

I shorted together the left and right channels from the Line Out jack
on the back of the K3, and fed them to right input of computer sound
card.  (The left input of sound card is connected to a TS-850, for
SO2R.)

I was concerned that bridging the two audio channels in this way would
cause the diversity separation in the headphones to be lost (e.g., when
operating CW, and having the bridged audio line for RTTY decoding still
connected).  But the headphones seem to still work as before, with
separate channels audible, L-R.  I'm guessing there's a buffer amplifier
that feeds the rear panel line out jack, so that shorting those channels
doesn't effectively short the other audio L/R outputs (e.g.,
headphones).

Does anyone know for sure?  'Anyone see a downside to this approach?

(I recognize I might be trading one problem for another: instead of QSB
in one channel, I now might sometimes have the L- and R-channels equal
in amplitude and out of phase, leading to a nil combined signal for the
decoder at odd intervals.  But that seems a low probability.)

Tnx,

/Bill, K2PO

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[Jack Smith-6]

Classically, in ye olde days of mechanical printers, diversity combing
was done post detection in the modem. Two receivers feeding two modems,
and the detector outputs of the two modems were combined with a
switching device that selected the output with the best SNR.

With CW, the operator's wet-ware can separate the two channels and
perform a version of best channel selection.

Jack K8ZOA

On 2/18/2013 6:15 PM, [hidden email] wrote:

> I'm wondering if diversity receive might help with RTTY decoding, to
> reduce deep fades.
>
> I shorted together the left and right channels from the Line Out jack
> on the back of the K3, and fed them to right input of computer sound
> card.  (The left input of sound card is connected to a TS-850, for SO2R.)
>
> I was concerned that bridging the two audio channels in this way would
> cause the diversity separation in the headphones to be lost (e.g.,
> when operating CW, and having the bridged audio line for RTTY decoding
> still connected).  But the headphones seem to still work as before,
> with separate channels audible, L-R.  I'm guessing there's a buffer
> amplifier that feeds the rear panel line out jack, so that shorting
> those channels doesn't effectively short the other audio L/R outputs
> (e.g., headphones).
>
> Does anyone know for sure?  'Anyone see a downside to this approach?
>
> (I recognize I might be trading one problem for another: instead of
> QSB in one channel, I now might sometimes have the L- and R-channels
> equal in amplitude and out of phase, leading to a nil combined signal
> for the decoder at odd intervals.  But that seems a low probability.)
>
> Tnx,
>
> /Bill, K2PO
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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[Gary Hinson]

I guess this could be done in software these days.  It is possible to feed
left and right channels to two separate RTTY decoder instances and
interpolate the decodes by eye at the level of the decoded text, but I'd
have thought some cunning software ought to do a better job of
comparing/combining signals using their strengths, SNR or some other quality
measure, bit-by-bit.  Or something.

73
Gary  ZL2iFB

> -----Original Message-----
> From: [hidden email] [mailto:elecraft-
> [hidden email]] On Behalf Of Jack Smith
> Sent: Tuesday, 19 February 2013 12:51 p.m.
> To: [hidden email]
> Subject: Re: [Elecraft] Bridging L-R of stereo Line Out for single channel
> diversity RTTY
>
> Classically, in ye olde days of mechanical printers, diversity combing was
done

> post detection in the modem. Two receivers feeding two modems, and the
> detector outputs of the two modems were combined with a switching device
> that selected the output with the best SNR.
>
> With CW, the operator's wet-ware can separate the two channels and
> perform a version of best channel selection.
>
> Jack K8ZOA
>
> On 2/18/2013 6:15 PM, [hidden email] wrote:
> > I'm wondering if diversity receive might help with RTTY decoding, to
> > reduce deep fades.
> >
> > I shorted together the left and right channels from the Line Out jack
> > on the back of the K3, and fed them to right input of computer sound
> > card.  (The left input of sound card is connected to a TS-850, for
> > SO2R.)
> >
> > I was concerned that bridging the two audio channels in this way would
> > cause the diversity separation in the headphones to be lost (e.g.,
> > when operating CW, and having the bridged audio line for RTTY decoding
> > still connected).  But the headphones seem to still work as before,
> > with separate channels audible, L-R.  I'm guessing there's a buffer
> > amplifier that feeds the rear panel line out jack, so that shorting
> > those channels doesn't effectively short the other audio L/R outputs
> > (e.g., headphones).
> >
> > Does anyone know for sure?  'Anyone see a downside to this approach?
> >
> > (I recognize I might be trading one problem for another: instead of
> > QSB in one channel, I now might sometimes have the L- and R-channels
> > equal in amplitude and out of phase, leading to a nil combined signal
> > for the decoder at odd intervals.  But that seems a low probability.)
> >
> > Tnx,
> >
> > /Bill, K2PO
> >
> >
> __________________________________________________________
> ____
> > Elecraft mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:[hidden email]
> >
> > This list hosted by: http://www.qsl.net Please help support this email
> > list: http://www.qsl.net/donate.html
> >
>
> __________________________________________________________
> ____
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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