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This message is prompted by the "Misek/Lankford/Ratzlaff proto test" thread
that I found when perusing the 3-week IRCA digest recently sent, Interestingly
I had not seen any of that discussion in the daily digests during that time
period.
Phasing two or more antennas has been in regular use in the broadcast industry
since the earliest directional arrays in the 1920's or 1930's.
In aircraft and shipboard direction finding applications (RDF), the combination
of a figure-of-8 loop and an omnidirectional vertical whip to produce a
single-direction null, cardioid (heart-shaped) pattern, has been in regular use
since at least World War II.
In medium-wave DXing, the first usage of phasing (that I know about) was by
Gordon Nelson (WA1UXQ) in the late '60s and early '70s, His unit consisted of
a series inductor, tuning capacitor, and low range (500 ohm or less)
potentiometer coming from each antenna jack. The other end of each L-C-R line
went to a transformer with its primary center tap to ground; the transformer
secondary was connected to the output-to-receiver and ground coaxial jack. The
primary transformer leads could be reversed to flip phase 180 degrees. Each
line would be tuned to resonance individually, the user then adjusted pots so
that station-to-null amplitude on each antenna was roughly equal. Phase
shifting was accomplished by adjusting one capacitor or the other off its
peaked setting. With certain types of antennas, namely lower impedance ones,
the set-up worked reasonably well. The Q (selectivity) and, as a result, phase
shifting range, could sometimes be inadequate.
Nelson let me borrow one of his phasers around 1974 and I had some moderate
success with the thing at Menotomy Rocks Park (Arlington, MA) and the following
year much greater success at Willis Pond (Sudbury, MA) with two 1200 ft. (366m)
Beverages.
Other DXers such as Bill Bailey (W1YPK) and Chuck Hutton (WD4ELO) were also on
the phasing bandwagon using variations on Nelson's design.
After a while Ron Schatz of FL came out with the specific type of phasing known
as the Loop Sense Cardioid Array. This was basically the loop-versus-whip RDF
system of aircraft direction-finding fame tweaked for the MW DX application.
By the late '70s I had changed the series L-C-R application over to a parallel
L-C-R tank on each line with a tap on the inductor for low impedance matching.
Different input coupling values, usually capacitive, were tried so that all
needed phase shifts could be accommodated without excessive insertion loss.
Passive phasing was the typical method used in strong-signal urban
environments, but, for operation out in the "boonies", FET buffer amplifiers
were inserted after the tank circuits for substantially more sensitivity. The
National Semiconductors LH0033CG and LH0063CK buffers were workhorses in my
designs. I still have a flea-market stash of these long-obsolete parts though
better designs, such as Lankford's, have come along since.
In the '80s the next development in phasing was use of off-the-shelf tapped
delay lines. Gerry Thomas and Dallas Lankford got involved with those and I
experimented with them as well.
The "bridge" circuit, as used in some of my "DXP" and Gerry Thomas' Quantum
Phasers, was well established by the '90s. Meanwhile Misek, Lankford, and
Ratzlaff were working on delay-line circuits created from discrete inductors
and capacitors rather than from the "canned" units used previously. These
allowed for finer adjustments.
Phasers were developed for the ham radio community, initially marketed as
"noise cancellers" and later acknowledged for abilities to null actual
interfering stations and do beamforming. JPS ANC-1 and the MFJ 1025 and 1026
models were moderately-priced entry level units. The more sophisticated DX
Engineering NCC models came later.
By the early 2000's, two developments came along to rock the MW DX hobby in
many ways and change what DXers did with phasing.
The first development was wider-spread use of terminated cardioid-pattern loops
with names such as Ewe, Kaz, SuperLoop, Flag, Bowtie, DKAZ, and DHDL.
Especially on the two coasts of North America, with foreign DX often in the
opposite direction from much of the domestic interference, these antennas were
a godsend since they produced a desirable directional pattern over good
bandwidth without all that phasing unit knob twisting. Furthermore, the
pattern held up even with rather small antennas that could fit in a suburban
lot or even on the roof of a vehicle. Until about 2000, my car roof beach DX
set-up that I trotted out to Granite Pier and other locales was a bidirectional
loop phased against an active whip. The system was very effective in nulling
"pests" from NYC to the southwest as Europeans from the northeast boomed in
around sunset. Moving about the dial involved periodic phase / amplitude
re-adjustments to maintain the cardioid null one frequency to the next.
Terminated loops largely took away that aggravation. Use of a phasing unit was
reduced to more of a "niche" activity when you really needed to get to a 40 dB
null on a blaster such as 1130 WBBR: the 20 or so dB null of the terminated
loop wasn't cutting it to get to the subdominants from Brazil etc. In general
the phaser wasn't nearly as vital an item in the toolbox.
Right on the heels of the terminated loop revolution came the second big
development of the 21st century: spectrum-storing SDR receivers. Initial
offerings such as the SDR-IQ around 2006 only could capture a small to moderate
slice of bandwidth, e.g. 190 kHz. At that point, the one-frequency-at-a-time
DXing paradigm still largely held sway and if a null that was great high-band
didn't work low-band without some knob spinning, so be it. The real revolution
got going about 2008 when the Perseus came out. When operated with a
higher-end computer, a full 1600 kHz of bandwidth could be captured. Typically
a DXer would do 150-1750 (LW + MW) or 450-2050 (MW + 160m). The desire for an
antenna pattern that behaved the same way over the whole band became more
important. Phasers that were tuned L-C had largely fallen by the wayside by
then anyway. A consistent time delay setting and flat gain over bandwidth
became valued parameters. Much of the time phasing was applied to deliberate
situations, especially two identical-pattern and -gain antennas displaced a
certain distance (100-200 ft. / 30-60m typically) in end-fire or side-by-side
layouts. Two disparate pick-up antennas, such as loop versus random wire into
a tree, a common '70s set-up, cannot cut the mustard for something like a 30 dB
west null band-bottom to band-top.
Phasing is still a relevant tool in 2018 just as in 1978 but how DXers put it
to use has changed to a fair extent. Live DXing, single channel at a time, is
often still employed and can sometimes get you to a custom hand-adjusted null
better than what a broadband compromise might produce. A mix of "new school"
and "old school" techniques leads to the greatest enjoyment of the hobby.
Mark Connelly, WA1ION
South Yarmouth, MA
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