[Fwd: LF: Signal enhancing noise canceller]

André Kesteloot akestelo@bellatlantic.net
Tue, 09 Jun 1998 10:41:29 -0400

Alan Gale wrote:

> At 13:10 27/05/98 +0000, you wrote:
> >I, too, was excited by this description, and got the chance to test
> >it. Result: it does not work at LF (well, it might help a bit at
> >Radio 2 on 198kHz). There is simply not enough gain in the noise amp
> >at LF to be of any use at all.
> >
> >Great idea, though. I am conveinced that an effective noise canceller
> >at LF would be a boon. Nearest I have got to this was to couple my
> >loop antenna to the ferrite rod of an amplified ferrite antenna, and
> >then rotate each to alter the combined radiation pattern. Gives both
> >peaks and troughs.
> >
> >Mike, G3XDV (IO91VT)
> Hi Mike & David,
>         A number of Dxers tried these units for Medium and Long Wave Dxing,
> and found a few problems. The following is a copy of a review by Mark
> Connelly WA1ION, who found some very alarming results at LF, but proposed
> a few modifications that would make them useable and effective down here.
> This is very long piece, but is very comprehensive and might help you
> to decide if it's worth buying!
>                 73 and Good LF, Alan.
> ---------------------------------------------------------------------
> This is a message from wa1ion@ix.netcom.com (Mark Connelly)
> Review of MFJ-1026 Phasing Unit
> Mark Connelly, WA1ION - 20 JUL 1997
> A recently-released product has been getting quite a bit of
> attention in radio-related E-mails, Internet bulletin boards, Web
> pages, magazines, and personal correspondence.  The device is the
> MFJ-1026, described as a "Deluxe Noise Cancelling Signal Enhancer"
> by its manufacturer MFJ Enterprises, Inc. (see company address
> information at the end of the article).  DXers will recognize
> the MFJ-1026 as a "phasing unit".  The list price is US $ 139.95;
> outlets such as R & L Electronics of Ohio are selling it at prices
> as low as $ 115.  It offers the ability to null interference,
> whether from electrical noise sources or actual transmitters.
> This is accomplished by creating a 180 degree phase shift between
> two antennas that are presenting equal-amplitude "pest" signals
> that cover desired DX.  There is a similar model, MFJ-1025, which
> does not have the built-in whip / preamplifier option.  The '1025
> sells for about $ 20 less.
>         A little bit of phasing unit history is in order here.
> Phasing units have been around for a long time, but most of these
> have been homebrew models built by a few dedicated DXers.  In the
> 1960's, I built some hit-or-miss L-C-R tuners / combiners to use
> at my Menotomy Rocks Park antenna farm and by the early '70s I had
> one of Gordon Nelson's boxes up and running ahead of my R-390A.
> Master Trans-Atlantic DXer Bill Bailey was also using a Nelson-
> built box at the time.  160-m hams such as Victor Misek were also
> experimenting with phasing circuits for steerable nulls.  Producing
> a null in the opposite direction of a peak turned out to be a big
> advantage over loops, especially in hearing European stations here
> in the Boston area with the New York City (and other) "pests" off
> the back of the beam.  In the early '80s, moving onward from the
> L-C-R units, Gerry Thomas took a bold step into broadband phasing
> with his delay-line-based Phase One.  His research led to my DL-1,
> DL-2, and DCP-2 models.  In the U.K., Graham Maynard became well
> known for the units he built.  As the 1990's opened, there was
> still very little in the way of commercially-available hardware
> despite the fact that many of the serious international DXers
> were using the homebrew units both at home and on Beverage
> DXpeditions to hear exotic stations that could not have been
> logged any other way.  A device called the S.E.M. QRM Eliminator
> had minimal promotion and little market penetration.  It used a
> tapped delay-line in a circuit similar to Gerry Thomas's Phase One.
> By 1993 (I think), the JPS ANC-4 model came onto the scene.  In a
> trend that has followed all of the commercial units, advertising
> pointed out that elimination of local electrical noise was the
> primary use.  One channel of the ANC-4, therefore, was a very-high-
> gain stage driven by a short "noise gathering" whip.  This arrangement
> didn't seem particularly well suited to the DXer's more common
> objective of using two similar fairly-low-noise good-gain outdoor
> antennas to phase in order to remove co-channel (or adjacent channel)
> interfering STATIONS rather than NOISE.  Noise was often easily
> discarded by using noise-reducing balun transformers with "quiet
> grounds".  This idea - promoted by Dallas Lankford, Nick Hall-Patch,
> and others - can get electrical noise out of the equation even ahead
> of the phaser, leaving it with the considerably more interesting job
> of removing dominant stations.  A few DXers got ANC-4's, but the unit
> was prone to overload on its so-called "noise" channel and nulls
> seemed to be hit-or-miss because of sometimes-inadequate level-
> balancing and phase-adjusting range.  Demand for homebrew units
> continued unabated as Al Merriman and I can testify.
>         In 1997, the MFJ-1026 has made a big "splash" because it
> is likely the first widely-available commercially-produced antenna
> phasing unit that can be made to work for medium-wave DXers.  I say
> "can be made to work" because some modifications must be made to the
> stock version unit available at the time of this writing.
>         The "long and the short of it" is that the brochure advertising
> the unit claims performance "down to VLF", customarily taken to be
> 10 kHz or so, when several E-mail communications with MFJ personnel
> indicated that the unit comes equipped with high-pass input filtering
> designed to attenuate frequencies below the 160-m ham band.  Indeed
> the lower one goes below 1.8 MHz with the stock unit, the worse the
> insertion loss gets.  Measurements taken here indicate losses of 8 dB
> at 1600 kHz, 16 dB at 1000 kHz, and 27 dB at 530 kHz.  By the time
> you get down to the 153 - 279 kHz European longwave broadcast band,
> the thing has so much loss (over 35 dB) that it might as well be a
> dummy load.
>         Aside from the insertion loss, inadequate phase shifting
> range on lower frequencies was encountered in some situations.
> Oscilloscope testing showed approximate phase shift ranges as
> follow: 200 kHz = 65 deg., 400 kHz = 94 deg., 600 kHz = 113 deg.,
> 800 kHz = 125 deg., 1100 kHz = 150 deg., 1500 kHz = 156 deg., and
> 2000 kHz = 169 deg.  With the SW3 Phase Normal / Invert switch of
> the MFJ-1026, dependable nulls could be produced if the R16 phase
> range control gave 180 degrees of adjustment.  It turns out that
> if you can easily swap the two inputs, a phase shift adjustment
> range of as little as 90 degrees will produce nulls.
>         Fortunately the modifications that have to be made to
> give the MFJ-1026 competent performance from 300 to 1800 kHz are
> quite simple.  The MFJ-1026 schematic is shown on page 12 of the
> instruction manual supplied with the unit.  The circuit board is
> well marked with the component designators.
>         Modification 1 will increase sensitivity below 2 MHz:
> * Remove L3, L4, R26 (main input channel); L5, L6, R27 (auxiliary
> input channel)
> * Change C8 and C16 from 680 pF to .01 uF
>         Modification 2 (swap switch) will ensure adequate phase
> shifting range above 300 kHz (these instructions may differ from
> prior E-mail postings):
> * A double-pole / double-throw (DPDT) "swap switch" (Radio Shack
> 275-614, or equivalent) is added in available space near the upper
> right hand corner of front panel.
> * Separate the middle pin (wiper arm) of each antenna gain pot
> from the circuit board: these are R20 (Auxiliary Antenna Gain)
> and R9 (Main Antenna Gain).
> * Install a wire from the R20 middle pin to swap switch section #1
> arm.
> * Install a wire from the R9 middle pin to swap switch section #2
> arm.
> * Install a short wire from swap switch section #1 "normal" contact
> to swap switch section #2 "swapped" contact.
> * Install a short wire from swap switch section #2 "normal" contact
> to swap switch section #1 "swapped" contact.
> * Locate the Q5 and Q8 transistors.  Each of these transistors has
> one side having two leads (these are the drain and source leads).
> The other side of each transistor has a single lead (the gate lead).
> Solder pads are located on plated-through holes immediately adjacent
> to the Q5 and Q8 gate leads.  These pads will be wired to the swap
> switch in the next two steps.
> * Install a short wire from swap switch section #1 "normal" contact
> to the plated-through hole solder pad that connects through the
> circuit trace to the Q8 gate lead.  Alternately, instead of going
> to that point, you could wire to the circuit board pad which had
> previously been wired to the now-cut R20 arm pin.
> * Install a short wire from swap switch section #2 "normal" contact
> to the plated-through hole solder pad that connects through the
> circuit trace to the Q5 gate lead.  Alternately, instead of going
> to that point, you could wire to the circuit board pad which had
> previously been wired to the now-cut R9 arm pin.
>         With the DPDT switch set to "normal", the switch completes the
> previously-wired paths: R20 arm to Q8 gate; R9 arm to Q5 gate.  In its
> "swapped" position, the R20 arm gets connected to the Q5 gate and the
> R9 arm gets connected to the Q8 gate.
>         A couple of minutes spent studying the schematic and board
> layout should make it obvious how to install these modifications.
> An additional modification suggested by Al Merriman is to remove
> the existing two Antenna Gain knobs and the one Phase Control
> knob and substitute larger knobs, such as Radio Shack part number
> 274-416 (diameter = 1" = 2.54 cm).
>         So now you've got the modifications installed and it's time
> to put the unit into use.  If you're using two relatively short
> antennas, these should be run out at a right angle to each other
> to prevent collateral nulling of both desired DX stations and
> "pests".  With two wires at a right angle, the best null / peak
> axis will be along the bisector (the line that divides the angle
> in half).  Longer antennas (over 150 m / 500 ft.) can be run closer
> to parallel and still produce good nulls, especially if there is
> some separation (1/8 wavelength or so) between them or if they
> are of somewhat different lengths or if one is terminated and
> the other is not.  E-mail correspondence with Tom Rauch (W8JI)
> brought up another interesting possibility.  If two similar small
> active broadband antennas (e.g. MFJ-1024 whips) are separated by
> 1/16 to 1/4 wavelength, good nulling performance can be expected.
> The line drawn between the two antennas would describe the best
> peak / null axis of cardioid patterns to be produced.  One-sixteenth
> wavelength at 500 kHz (or 1/4 wavelength at 2000 kHz) turns out to
> be 600/16 = 37.5 m = 123 ft.  Using two broadband active whips
> (with coaxial feedlines of about 19 m each) wouldn't be a difficult
> experiment to try.  The Robbins Road DXpedition site in Plymouth,
> MA would be ideal because the road has no power lines along it
> and its orientation is on an approximate 70 deg. / 250 deg. bearing
> axis (degrees clockwise from due north).  One whip 19 m along the
> road ahead of the car could be phased against the other one 19 m
> behind it.  This should be quite effective for nulling out
> NY/NJ/PA/OH domestics (at about 250 deg.) to clean up Europeans
> coming in on bearings of about 70 deg.  Tom Rauch also mentioned
> using broadband loops instead of broadband whips, but I haven't
> had much experience with untuned loops that have both high
> sensitivity (low noise floor) and good strong-signal handling
> characteristics (minimal intermodulation products).  Two broadband
> loops could be spaced 1/16 to 1/4 wavelength and oriented the same
> way, or they could be located closer to each other and pointed at
> a right angle to each other as in the old "goniometers".  Also, a
> co-located active whip / broadband loop could be used for loop-
> sense cardioid array (LSCA) operation (a la Ron Schatz).
>         The MFJ-1026 can be operated with a ham transceiver as it
> has built-in transmit / receive (T/R) switching on its main antenna
> input.  I suspect that the reviews of the unit in amateur magazines
> such as QST and CQ will cover this aspect of operation.
>         The auxiliary channel input can be from the built-in whip
> antenna (that goes through an internal preamplifier) if the front
> panel Pre-Amp switch is set to ON.  Otherwise, whatever antenna
> you've connected to the rear panel auxiliary antenna jack will
> be fed to the Auxiliary Antenna Gain pot.  I have phased the whip
> against Main antenna inputs ranging from tuned loops to untuned
> random wires.  The internal whip on a modified MFJ-1026 has
> reasonably good sensitivity, especially above 800 kHz.  Even at
> 530 kHz, the internal whip was able to discern Turks & Caicos at
> threshold level (about S2 to S3) on groundwave from a receiving site
> in Harwich, MA on Cape Cod.  This is on par with the sensitivity of
> the Quantum and Kiwa loops.  For comparison, an outdoor sloper to
> the top of a 20 m pitch pine tree at the Harwich site gives a Drake
> R8A S-meter reading of about S6 on Turks & Caicos - 530 groundwave.
>         There are four potentiometers (pots) on the front panel of
> the MFJ-1026 and there are four switches (five when you consider
> the user-added Swap Switch).  The potentiometers are T/R delay (R3),
> Auxiliary Antenna Gain (R20), Phase (R16), and Main Antenna Gain
> (R19).   Switches (besides the Swap Switch) are Power On / Off (SW1),
> Pre-Amp On / Off (SW4), Freq. High / Low (SW2), and Phase Normal /
> Invert (SW3).
>         The T/R Delay control is only of concern if you will be
> transmitting as well as receiving.  The Power On / Off switch sends
> the Main antenna straight through to the receiver if set to OFF.
> The Freq. High / Low switch is usually set LOW for frequencies
> from 300 kHz to 7 MHz, either LOW or HIGH for 7 to 12 MHz, and
> HIGH for 12 to 30 MHz.
>         The instructions in the MFJ-1026 manual are clear and will
> get the first-time user into the nulling "game" without much trouble.
> This is an easy-to-use unit compared to the L-C-R and delay-line
> phasers which preceeded it.  I would summarize operation as follows:
> * Set the (SW2) Frequency switch to LOW for medium-wave use.  Set
> the Auxiliary Gain (R20) fully clockwise and the Main Gain (R9)
> fully counterclockwise (anticlockwise) and take note of the strength
> of the station to be nulled.
> * Then set the Auxiliary Gain fully counterclockwise and the Main
> Gain fully clockwise and take note of the strength of the station
> to be nulled.
> * If the reading was lower with Main Gain fully clockwise, temporarily
> set it counterclockwise and set Auxiliary Gain to get the reading that
> you had with maximum Main Gain.  Then put Main Gain back to fully
> clockwise.
> * On the other hand, if the S-meter reading had been lower with
> Auxiliary Gain fully clockwise (rather than with Main Gain that way),
> set Auxiliary Gain fully counterclockwise and set the Main Gain
> to get the reading you had with maximum Auxiliary Gain.  Then put
> the Auxiliary Gain back to fully clockwise.
> * Rotate the Phase control (R16) to look for a null.  If the null
> isn't obvious, or if it tends to be at either end of the Phase
> control's range, try the opposite position of the Phase Normal /
> Invert switch (SW3) and rotate the Phase control again to search
> for a null.
> * If a satisfactory null still hasn't been achieved, try the opposite
> position of the added Swap Switch and repeat the previous step.
> * Once the correct combination of Phase control, Normal / Invert,
> and Swap Switch position has been arrived-at, make small interactive
> adjustments of the non-fully-clockwise Gain control and the Phase
> control until the deepest possible null has been acquired.
> Subdominant signals, if present, should be evident.
>         If the active circuits in the MFJ-1026 get overloaded by
> strong local stations, use moderate-Q tuned inputs such as loops or
> L-C tuned whips/wires - or, in cases of untuned wire inputs, just
> use less gain (as selected by the two 250-ohm Gain pots).
>         "Real life DXing" MFJ-1026 field tests were done on Saturday,
> 26 JUL (local) from the Robbins Road - Holmes Field beach-DXpedition
> site located off Route 3A in Plymouth, MA (approx. GC= 70.68 W /
> 41.98 N).  I used the Drake R8A receiver.  Both the R8A and the
> MFJ-1026 were powered from the car battery.  Two 90 ft. / 27 m
> wires lying on the ground were used.  This (admittedly less-than-
> ideal) set-up had been used with delay-line and other phasing unit
> designs previously, so I had a feel for what to expect.  The "main"
> antenna for the MFJ-1026 ran on a slight downslope along the side
> of Robbins Road straight towards the sea at a bearing of about
> 70 degrees.  The "auxiliary" wire ran out at a right angle into an
> open field of grass at an approximate 160 degree bearing.  I was
> on site at about 7 p.m. local / 2300 UTC.  This is about an hour
> before sunset.  I felt that one of the big challenges would be to
> null WPLM-1390, located less than 2 miles / 3 km from the site.
> Luckily, its very large signal did less overloading damage than
> WRKO-680 does back at home near the Shawsheen River marsh.
> Nulling WPLM a good 50 dB was easy !  It wasn't too long before
> evidence of co-channel skip stations from ME, NY, and VT started
> bubbling in behind the nulled WPLM audio.  Better yet was rather
> good audio from Netherlands on 1395 heard somewhat later !  The
> stations that the MFJ-1026 had the most trouble nulling were those
> with high-angle skip, especially if some groundwave was blended in.
> The stations on the top end of the dial, such as WNRB-1510, were
> particularly troublesome in this regard.  Null control settings
> required constant adjustment, especially in the period from an
> hour before sunset to an hour after.  The best sustained null
> depth I could manage on stations such as WNRB, WDCD, and WQEW was
> about 15 dB (although momentarily-deeper nulls popped in and out).
> Shortwave DXers will probably experience similarly "jumpy" results
> above 2 MHz.  Pure "groundwavers" like WPLM and longer-skip / lower-
> frequency stations such as WLW-700 nulled more deeply and for greater
> time intervals between required control re-adjustments.  These
> results are consistent with those found for any previous-used
> phasing scheme, whether delay-line, tuned L-C, or other.
>         As the evening progressed, the MFJ-1026 / phased wires set-up
> proved its value as numerous Trans-Atlantic stations were logged.
> Some of these came in fine on the 70-degree "Euro-wire" without the
> need for phasing, but, in a number of instances, phasing the two
> wires made the difference between a slop-plagued DX signal and
> crystal clarity.  The two Croatia stations (1125 and 1134) come
> to mind.  WBBR-1130 New York has a VERY strong signal at night here
> in eastern Massachusetts.  Indeed, outside the immediate groundwave
> zones of locals, it's one of the five strongest stations night after
> night.  When I was tuned to 1134, Croatia was running a good S9+20,
> but it was still trashed by WBBR slop at times - even on the "Euro-wire".
> With a few quick twists of the controls on the MFJ-1026, WBBR was
> reduced by better than 20 dB and Croatia-1134 roared in with absolutely
> beautiful audio.  On peaks, it was stronger than what was left of WBBR.
> Not only did the phasing accomplish a nice clean-up on 1134, but also
> the much-weaker Croatian on 1125 was brought into the clear with just
> a bit of co-channel flak from Spain.  Prior to phasing, it didn't
> have a ghost of a chance against the barrage of WBBR slop.
>         Earlier on 26 JUL, I had done a few daytime DX tests of the
> MFJ-1026 from Harwich, MA on Cape Cod.  The first battery of tests
> involved feeding a Quantum Loop into the MFJ-1026 "main" input and
> using the 1026's built-in broadband active whip as the "auxiliary".
> With the loop at normal (i.e. high) Q, audio null depths only reached
> about 20 dB (versus better than 40 dB for carrier).  This is
> consistent with previous nulling scenarios where a high-Q tuned
> source is phased against a broadband one.  You get what sounds like
> a double-sideband suppressed carrier signal.  If the desired DX is
> more than 20 dB below the dominant, you probably won't hear it even
> during stable midday conditions.  Q-spoiling the Quantum Loop (15K
> resistor shunting the L-C tank) increases nullability of "pests"
> maybe to 30 dB, but the loop's usable sensitivity is compromised.
> At night, this is probably a non-issue (except in aurora), but
> during the day you need every bit of signal you can squeeze out
> of the small loop.
>         A second battery of tests at Harwich used two wires at a
> right angle (similar to the set-up employed at Plymouth).  Daytime
> nulls were smooth ("like butter" some would say).  WGAN-560 was
> easily dumped to reveal WHYN, near-equal WPRO and CFCY on 630 could
> each be brought up alone, much the same on 740 with WJIB and WGSM,
> WJTO on 730 was nulled a good 30 dB to pull out WACE over CKAC,
> strong WCLZ-900 was phased under the co-channel CKDH/WMVU mix,
> WZNN-930 easily surrendered to CFBC, and so forth.  Nulling with
> two wires was decidedly better than any loop-versus-whip or loop-
> versus-wire scheme.
>         Once the MFJ-1026 is modified, it makes a very competent phasing
> unit that will undoubtedly bring the technology into the hands of many
> DXers who have not previously experienced its value in bringing new
> stations out of "the mud".
> Miscellaneous information:
>         Power requirements: 12 volts DC at 150 mA
>         Size: about 21 cm wide X 6.5 cm high X 15 cm deep
> Appendix: MFJ Ordering Information
> Webpage: http://www.mfjenterprises.com/mfj/order.html
> TECHNICAL INFORMATION: (601) 323-0549 or "jshurden@mfjenterprises.com"
> MAIL ORDERS: MFJ Enterprises, Inc.
>              P.O.Box 494
>              Mississippi State, MS 39762, USA
> TOLL-FREE (DOMESTIC): 1-800-647-1800
>                       300 Industrial Park Rd.
>                       Starkville, MS 39759 USA
> CREDIT CARDS: Visa, MasterCard, American Express, or Discover
> FOREIGN ORDERS: U.S. funds only
>         ----------------------------------------------------------------------
>         From:           Alan Gale G4TMV
>         Location:       North-West England. IO83VP Lancs 53:39.3N 2:10.6W.
>         Equipment:      Kenwood TS830M + Datong PC1 & VLF Converters + FL3.
>                         Sony ICF 2001D. G5RV, Marconi T, various Spiral Loops.
>         Interests:      Search & Rescue,Beacons,Maritime,Aero,Scanning,TV DX.
>         Editor of:      Bi-monthly 'Beacons & Utes' column, Medium Wave Circle.
>                         Quarterly 'Links FM' column British FM & TV Circle.
>         MWC Website:    http://www.geocities.com/Hollywood/5613/mwc.html
>         BFMTVC Site:    http://freespace.virgin.net/skywaves.dx
>         ----------------------------------------------------------------------