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- Subject: phasing units, then and now
- From: Mark Connelly <markwa1ion@xxxxxxx>
- Date: Fri, 6 Jul 2018 23:18:01 -0400
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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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