For WQ6X it's: Filters, Filters and MORE Filters

 

 

 

 

 

 

 

 

 

 

 

During recent weekends with a significant lull in contest activity, I have been rerouting
the audio cables behind the scenes of the portable setup I maintain at W7AYT's QTH
in Concord.

Having recently reintroduced a classic Radio Shaft 15-Band stereo equalizer (not shown in the
above photo) back into the audio line, I marveled at the morass of patch cables behind-the-scene enabling it to all work more-or-less with minimal artifact (i.e., unwanted signal interaction).

The transceiver setup in Concord is actually 3 units:

• A Classic (2009) Yaesu FT-2000
• A Classic (2007) ICOM 7000
• A not-so-Classic Elecraft K3/0 - for remote K3 radio access

Because Stereo-Cw is at the heart of ALL the audio filtering employed, a pair of Classic Autek QF-1A analog filters (A) front-end the audio line.  The filters which follow, shape the stereo audio differently for each ear - an MFJ-784 for the left ear and a pair of NIR DSP filters for the right ear.

The mixing box (B) enables mixing audio from the FT-2000 and the K3/0 through the array of audio filters, with capability to add another pair of devices.  The USB-powered unit contains OP-amp isolation with adjustable volume control for each channel.  Next to it (I) is an old-design 4-port
signal splitter unit which enables sending the audio to multiple filter inputs with a similar form
of device isolation insuring they get only the signals, NoT ground-loop voltages.

The Rockville 8-channel mixer allows listening to signals from the mixing box directly or by way
of a pair of MFJ 752 audio filters or DSP units - an MFJ-784 for the left ear and a pair of cascaded JPS (NIR-10 --> NIR-12) filters for the right ear.

A side effect of using older-style DSP units in parallel with analog boxes is the artifact that
is introduced in the form of an approximate 120ms signal delay created by the DSP unit itself. 
This problem has been resolved by adding a bypass-able AU Tool AP-411 device known as the
"Lip Sync Corrector" into the analog audio line introducing an audio delay that matches the
processing overhead of the NIR-10 + NIR-12 DSP devices in the opposite ear. 
A repurposed A / V switch allows the L-S-C to be switched-in or bypassed.

Overall, this combination of switches and filters allow for a number of different approaches
to massaging receive audio into something more readily understandable.

What about YOU?
Do YOU make use of external audio?
What secrets have You uncovered?