[CQ-Contest] Bleed thru problem

[VR2BrettGraham]

K6LA asked:

>I originally posted this to the Writelog (WL) reflector, but didn't get a
>response, so I'm trying here.
>I have two bleed through problems. The first only occurs when WL is running.
>When the AF on radio A is turned up past a certain point, it triggers the
>VOX on radio B, and vice versa. I use the radios' phone patch out to record
>audio via the computer sound card. When the phone patch out is disconnected,
>this problem goes away. So the problem appears to be in the computer sound
>card.
>
>The second problem is always there, whether WL is running or not. When the
>AF is turned up past a certain point on radio A, audio from radio A can be
>heard in the headphone for radio B, and vice versa. The audio runs through
>the W5XD Multi-keyer, so the problem appears to be there.
>
>Both these problems occur at audio levels higher than I would ordinarily
>use, so they are not fatal problems, but I would like to eliminate them
>both. I have tried using the WL audio mixer to find levels that work, but to
>no avail.

Dunno about the first, but the second sounds like something somewhere
is mixing the audio from the two radios together on purpose.

I currently record audio going to the headphones, so it was necessary
to defeat the mixing between L & R going on inside the switch box.  It
is easier on the ears if you hear a bit of the same rig in the other ear
(bit of left rig in right ear, as well as majority of right rig & vice versa),
but obviously this is not helpful for the recording.

That also would explain the first problem - audio from first rig is being
seen by second & that audio then mucks up its anti-VOX, since it isn't
audio from that rig, but the other one (anti-VOX is done by taking RX
audio, shifting it 180-degrees, then shoving it into the mic input,
therefore cancelling with the receiver audio as heard by the mic & as
a result not activating PTT - now imagine if that audio didn't match
the audio coming from that rig's receiver: VOX could be activated).

Ditch the VOX & remove the L/R mix, otherwise ditch the VOX &
record from somewhere else (like fixed level output for RTTY) so you
can keep the mix.  On radios with main & sub-RX & you want to
record the sub-RX audio also, the simple resistor as a combiner
(like the headphone mix) could cause the same sort of grief, so
rather than a simple resistor combiner, a little summing amp with
an op amp is in order.

73, VR2BrettGraham