[IRCA] The Sony SRF-59: now with Audio Phasing(!)

[satya@xxxxxxxxxxxx]

Hi all:

I recently purchased my second SRF-59, and it got me thinking about
experiments I did as a teen in the 1970's with stereo audio sources, and
how canceling the signal that is common to both channels (usually drums,
lead vocals, etc.) left only those elements that were "stereo-ized" such
as rhythm guitar, etc.  David Hafler was also doing this in the 1970's,
only he became somewhat famous for it with his surround sound circuit (see
for example http://sound.westhost.com/project18.htm) ? too bad I didn?t
have a patent attorney back then?

At any rate, the effect is essentially audio phasing, and is accomplished
by joining the negative leads of the two stereo sources (usually L and R
speakers outputs from a receiver) together without connecting this union
to the speaker.  The two positive leads are then connected to either
terminal of a single speaker (or two speakers in series).  Electrically,
the common voltage portions cancel each other out (i.e., the vocals have
the same voltage at either terminal of the speaker's voice coil, and it is
a draw, so the vocals disappear) and all you have is the audio that is NOT
common to the two (the tambourine, etc. is all you hear).  It makes for a
neat surround-sound effect.  As long as the common element (voice, etc.)
is EXACTLY the same in both channels (same frequency equalization, dynamic
range, etc.), it works like a champ.

It got me to thinking: if I had two DX audio sources, one that had only
the pest (i.e., point the antenna at a strong local and null the desired
DX target) and one that has both the pest and the DX target, in essence I
would have a pseudo-stereo source.  By using the audio phasing technique
described above, I should be able to make the pest disappear  by injecting
just enough of the first signal (pure pest) onto the second signal so that
the pest just disappears, leaving the DX target.  I tried this last year
with two different receivers and it didn't work at all, because the slight
difference in filters, antennas and audio signals were different enough
that the pest never really went anywhere.

Well, now I have two identical receivers - the SRF-59s!  I sacrificed an
audio patch cable in order to effect the circuit described above. 
Specifically, the audio leads from the two radios? headphone jacks consist
of a 1/8? mini stereo male-male audio cable cut in half, with all 3 wires
bared on each half.
1.  On each half-cable, twist its two positive leads together, resulting
in a mono source from that receiver.
2.  Next, twist the two negative leads from each cable together and
isolate this union with electrical tape or whatever.
3.  Now take the two positive leads from each cable (which themselves each
consist of that cable?s two stereo wires twisted together per Step 1
above) and connect those to either terminal of a single speaker. 
Alternately, this can be fed to a pair of mono headphones or, with a
mono-stereo adapter, to stereo headphones.  Mine is fed to my Olympus
WS-320M recorder ? same thing.
4.  Plug each of the 1/8? mini stereo male plugs into the SRF-59s, and
you?re ready!  First crank up the volume of the mixed pest/target signal,
then slowly increase the volume of the pure pest signal to start canceling
the pest out of the mixed signal.  The pest will fade, and you should end
up with much more, if not all, the DX target that was lurking underneath.

For the first test last night, I selected my local 630-KCIS, which can be
somewhat difficult to null or phase if I want to hear KXFD in Boise.   I
placed both of the SRF-59s into my two identical Terk loops to get some
signal (again, you must have the EXACT same set-up), pointed one straight
at my local 630-KCIS  and one away from it ? works like a champ!  KCIS
essentially disappeared, and KFXD-Boise was sitting there virtually all
alone!

Next I applied the set-up to blowtorch 680-KNBR and, upon equalizing the
volume from both barefoot units, KNBR disappeared!  There was nothing else
to take its place on this rather dismal night, but it was nice to have an
open channel?

At my QTH, beleaguered semi-local KXPA-1540 suffers from the IBOC hiss
coming from 1530-KFBK.  One receiver was pointed straight towards KFBK,
and the other half-way towards KXPA, not quite nulling KFBK.  Guess what ?
the IBOC hiss was virtually gone from KXPA!

KXL-750 is essentially a semi-local from Portland.  Apparently because of
it having both ground and sky wave components, phasing with two loops or a
Quantum Phaser has never really worked.  However, audio phasing on the
SRF-59?s worked well enough that I could comfortably hear the conversation
underneath from (I think) KOAL in Provo, Utah.  KXL's audio null
fluctuated a lot, but it was better than I could get with regular phasing.

Yes, some stations work better than others: for instance, I couldn't do
much of anything with KIRO-710 or KTTH-710 last night.  Also, some
stations are easily nulled or phased out of existence (remember, the
SRF-59 is a great null producer) so you don?t need to go to these lengths.
  However, this seems to be a valuable tool for many situations when an
electrical/magnetic null isn?t in the cards, and the IBOC hiss reduction
is very pleasing, both aurally and philosophically.  Besides, it is a
great excuse to buy another $15 radio!  You may not have the resources to
buy two Drake R8Bs, but two SRF-59s (and maybe two Terk loops) is probably
within reach of most of our pocketbooks.

I can?t emphasize enough how the two audio sources have to be identical
(same receiver, same antenna, etc.).  For example, using one SRF-59
barefoot and the other with a Terk loop produced enough of a sonic
difference that there was noticeable bleed-through of the pest; I think
the Terk tightens up the audio bandwidth too much.  Likewise, using an
SRF-59 and my Sony 7600GR was a complete failure, given the markedly
different audio characteristics of the two receivers? filters, audio
circuitry, etc.

One thing to watch: if you directionally null the pest too well with one
receiver, it may start to flutter, or change/color its audio frequency
balance, and it won?t match the other audio source very well, resulting in
bleed-through of the pest.  The technique seems to work best when I null
the desired DX target with one receiver (not necessarily maximizing the
pest, which still stand alone anyway) to produce the pest signal, and then
have the other receiver with more of a mix of the two without necessarily
fully nulling the pest; that way you have a similar pest audio signal in
both channels, which will more nicely cancel each other out.

An ergonomic tip - plugging the two audio channels into something with a
balance control (stereo receiver, etc.), which then feeds into the audio
phasing circuit, makes it a lot easier than constantly adjusting the
individual volume controls on the two SRF-59s all the time.

I wonder how this would work on canceling audio splatter on 9khz splits?.

Good luck!

73 ? Kevin S.
Bainbridge Island, WA

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