Tuesday, July 31, 2018

WQ6X SOUND PROCESSING: Maximizing the Art of Experimentation

As you may know, I love to knob-twiddle, but ONLY if pressing buttons and twiddling knobs will effect an improvement of the received signal. In the middle of the night, knob-twiddling helps alleviate operational boredom, helping to keep me awake.

A 20+ year old FT-1000mp is still contemporary
In March 2018 I published a couple of BLOG Entries detailing the many different aspects of processing RX audio from the Yaesu FT-1000mp during portable and contest operations:

Running a Yaesu FT-1000mp offers plenty of adjustable knobs useful for extracting weak signals
out of the noise. Unfortunately, most of those receive enhancement features (IF Shift/Width, NOTCH
& e-DSP) are functional ONLY with the Main-RX.  The Sub-RX is seriously lacking in interference reduction facilities, which is what makes external filter units so important.

For the 1000mp's Main-RX, I prefer to utilize outboard Autek QF-1A, JPS NIR-12 and MFJ-752 filters (in that order of usefulness). 

For the Sub-RX, because it sports no DSP auto-notch filtering, the JPS NIR-12 becomes a crucial addition.  While the bandwidth adjust controls of the NIR-12 are useful, I leave that filtering aspect to a QF-1A inserted between the XCVR and the NIR-12.

Pricewise, QF-1A's can easily be had for under $50.  JPS NIR-12's are much harder to come by and can fetch as much as $200+; altho the average price seems to be around $125.  When I bought an NIR-12 from W6SW, it had little use, which for me made it worth the $175 I paid. 
(List price was around $249.)

Based on the recommendation of Dr. Joel (W1ZR), because it is equipped with an output amplifying stage, it makes sense to put the NIR-12 AFTER the QF-1A in the FT-1000mp's Sub-RX audio line.  [CLICK HERE] to read my comments about Dr. Joel's recommendation.

This filter combination is very useful when running Multi-mode contest events such as state QSO parties, Field Day and the IARU HF championship on 40 meters.  It allows running a frequency on CW using VFO-A while using the Sub-RX to
look for SSB stations.

The Automatic Notch Filter (ANF) circuit in the NIR-12 does an excellent job of knocking out 40-meter shortwave broadcast carriers.  The bandpass filtering of the QF-1A peaks scuzzy SSB audio making it more readable.  Remember however
that being an audio-based filter, even though the carriers
are removed from the audio stream, any deleterious effects those carriers may have on the AGC circuits will still exist.

Cascading the QF-1A & NIR12 for the FT-1000mp's Sub-RX audio allows emulation of the Main-RX notch filter features.  The NIR-12 ANF is as effective as the ANF in the FT-1000mp.  The notch filter
in the QF1-A seems to be as effective as MP's manual notch filter.

Remember that the FT-1000mp Main-RX is equipped with I-F shift and width-reduction capabilities. 
While the Sub-RX is lacking in this respect, at anytime the A<-->B button allows swapping the VFO's
giving immediate access to the SHIFT/WIDTH functionality.

Technically the QF-1A is not equipped with any form of noise reduction circuitry, yet the PEAK and Bandpass filtering often result in an improved signal/noise ratio.

Although the NIR-12 IS equipped with
a Digital Noise Reduction (DNR) circuit, while it is continuously adjustable, I find the 4-position DNR switch of the Yaesu
FT-1000mp provides more effective "noise-softening" than does the NIR-12.

Additionally, altho the NIR-12 is equipped with audio bandwidth and frequency shift controls, being audio-based, their effect is not nearly as pronounced as the IF-based
SHIFT/WIDTH controls built into the Yaesu FT-1000mp's Main-RX.

In the 21st century, we have BOTH analog and digital filtering methods available for use in ALL
areas of our receiving equipment; the RF frontend, the many/various I-F stages and the front-end audio circuitry.

Surviving in contests and DX pileups require that we utilize every bit of technology available to us.  While older analog-style filters may seem primitive by today's standards, remember that they ALL utilize a primitive (originally undesirable) feature known as feedback.  Technically the DSP circuits
in today's modern radios don't utilize feedback, however the A-to-D and D-to-A conversion circuitry make extensive use of feedback.

WQ6X's FT-1000mp filter usage in May 2018
Additionally, remember that many filter techniques (such as noise-blanking and DSP noise reduction) often add their own distortion (i.e. noise) in the process.  I guess in the end, what matters is whether or not the signal I am attempting Q-5 copy on is in fact becoming more-copyable with all these filter buttons and knobs. 

In all my contest experience, while I've had mixed results with various external interference
reduction units, overall, the time, money and effort have been well worth it.  There are contest
certs in the WQ6X contest certificate binder that would certainly not be there had I not made use
of external audio shaping and filtering.

What about you?
What kind of external filtering equipment is used at YOUR QTH?

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