Radiosport: Learning - It's All about learning

 

 

 

 

 

"[S]He who does not learn from the past is doomed to repeat it".

As a radio amateur, for me, radiosport fulfills  3  main objectives

1. Satisfies My competitive nature.
2. Serves as an Emergency Preparedness Drill.
3. Encourages experimentation w/various hardware configurations;
   mainly on the audio end but also on the other [antenna] end as well.

"Back in the day" when the station configuration rarely changed (an ICOM-740, and a Dentron
Jr. Monitor tuner into a homebrew vertical), there was little to learn; it always worked, until it didn't anymore.  There was no remote operating; the closest thing to a DSP was the (American made) Autek QF-1A or the (British made) Datong FL-3 - BOTH IC-based (but analog) filters.  Then again, amazingly, the idea of using external audio filters never occurred to me at the time.

When we begin mixing analog and digital, unintended signal-alteration becomes the new concern.  On Cw, to some degree we rely on signal alteration (Peaking & Notching, etc.) to produce the desired signal-improvement effect.  With Ssb, all too often, attempts to reduce the noise-component succeed only in reducing overall intelligibility.

 

I recently looked at this problem in terms of unintended Binary-Beating which can occur when running Stereo-Cw ([CLICK HERE] to read that).  To use a Biofeedback term, "artifact" (unintended/false) signals are always a problem in the aural sense.

Once I glommed on to the Stereo-Cw idea, as each circuit was added one audio cable after
another was clipped (or otherwise modified/adapted) to fit each part of the expanding solution. 
As each individual unit is added to the overall solution, unintentional "ground-loops" often creep
into the audio-path.  Sometimes it seems we spend more time "sniffing out" the ground loops than
we do putting the circuit together in the 1st place.

Since last weekend's All Asian contest, I've been playing around with the audio paths between the FT-1000mp, Icom-7000, Elecraft K3/0 and the RockVille Mixer which (with a pair of switch boxes) routes the radios to the current lineup of external audio filters which include:

• a Pair of MFJ-752 "Signal Enhancer II" units
• a Pair of Autek Research QF-1A Ssb/Cw/Am Filters
• a JPS NIR-12 & recently added NIR-10 DSP filters
• an MFJ-784 DSP and a Radio Shaft DSP-40

Running each of the above filters in many configurations during contest and ragchewing
identified the following traits:

• The MFJ-752 filters are really NoT for Cw.  The Cw position selected by the mode knob accomplishes nothing more than switching in a pair of clipper diodes to effect a crude
  form of noise limiting.  The Ssb NL position of the MFJ-752C does a reasonable job of suppressing high frequency hiss for left ear listening and is positioned to process the Main-RX audio.  For Cw, the built-in Yaesu 500hz/250hz filters do a superb job.
• For the Sub-RX, an MFJ-752B has been modified, replacing the NL positions with connections to an ancient MFJ CWF-2 filter (installed inside the box).  The Ssb NL
  position now invokes the 180hz setting of the CWF-2 and the Cw NL position invokes
  the 80hz setting of the CWF-2.  This provides a reasonably narrow CW bandwidth for
  the sub-receiver.  The MFJ-752 filters are accessed by RockVille mixer channel CH3.
• The Radio Shaft DSP-40 is a unit acquired years ago that I just don't know what to do with, relegating it back to "sitting on the shelf" status; but this time, a shelf at the operating desk, reminding me that it too should be given consideration.
  
• Mixer channel CH-1, blends audio from the ICOM-7000, mainly for SWL'ing, but sometimes as a 3rd receiver.  Thanks to an excellent IF-DSP built-in to the transceiver,
  no outboard filters are needed, or even desired.
• Mixer channel CH-2 blends in audio from the K3/0 audio path.  Altho the K3 has a built-in IF-DSP, a 2nd switch connection to the radio can direct the audio thru channel CH-4. 
• The Stereo-Cw facility is invoked by a separate mixer channel - CH-4 - created by a pair of analog Autek QF-1A filters - one for each ear - cascading into separate digital DSP units.
  
• Mixer channel CH-4 can be switched to process audio from either the FT-1000mp or the K3/0.  With the left channel of CH-4 the Autek QF-1A fronts an MFJ-784.  While it's auto-notch facility is weak, the noise reduction and AGC buttons produce amazing effects.
• With the right channel of CH-4 the Autek QF-1A fronts either a JPS NIR-12 or (currently under evaluation) an NIR-10.  The Dynamic peaking of the NIR-12 provides an amazing noise-free threshold that is perfect for Cw, and to some degree ragchew Ssb.  Then again, if eliminating heterodynes is the BiG concern, there is no better auto-notch than the one
  built into the NIR-10.  The plan is to eventually "cascade" the NIR-10 into the NIR-12 for the right side Sub-RX audio, creating an equivalence to the FT-1000mp's built-in eDSP
  for the Main-RX.

 

 

 

 

 

 

 

 

 

 

 

 

The above points were all determined by Trial, Error and Learning. 
The pen-scribbled diagram overall says it all.  In order to effect that learning,
I participate in one of my favorite aspects of amateur radio - KNOB TWIDDLING. 
Altho I am hardly a perfectionist, I DO enjoy evoking an extra-bit of improved copy
on signals during a Hot-N-Heavy radiosport contest.

What about YOU?  What do YOU use to improve signal copy?

PLEASE!  Tell me all about it.