By Mark Connelly
This is a
quick "heads up" on field testing of the modified MFJ-1026 phasing
unit done on Saturday, July 26, from the Robbins Road - Holmes
Field beach-DXpedition site located off Route 3A in Plymouth,
MA (approx. GC= 70.68 W / 41.98 N).
Equipment: I used the Drake R8A receiver. Both the R8A
and the MFJ-1026 were powered from the car battery.
Antennas: Two 90 ft. / 27 m wires lying on the ground were
used. 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.
on site at about 7 p.m. local / 2300 UTC. This is about an
hour before sunset. The two wires were laid out, narrowly missing
a patch of poison ivy and some "dog dirt": just a couple of "the
hazards of DXpeditioning".
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 !
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. Physically-large
antennas often help to reduce some of the problems with jumpiness
and shallow null depth on short-skip and higher-frequency propagation.
There's only so much you can get out of physically-small antennas,
regardless of the phasing method employed. Theoretically, a computer-controlled
system could accurately "chase" the optimum null in real time,
but no one has made this idea a reality yet.
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. WQEW-1560 and WDCD-1540 would also be on the
"King Kongs of medium-wave skip" list.
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.
on July 26, 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.
The MFJ-1026's active whip, by the way, had good sensitivity and
low amplifier noise: above 800 kHz its usable signal capture was
comparable to that of the Quantum Loop at normal Q. Even at 530
kHz, it provided threshold daytime audibility of Turks & Caicos
on 530 kHz from Harwich: that's just about as good as the loop.
On an outdoor sloper to the top of a 20 m / 66 ft. pitch pine
tree, Turks & Caicos groundwave runs about S5 to S6 on the
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, WWNH-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.
with the MFJ-1026 was easier than with a JPS ANC-4 and most
of the homebrew units I've used over the last 30 years. It must
be stated that some rather simple, but totally necessary, modifications
had to be made to the stock MFJ-1026 to get it to up to "world
class" medium-wave performance.
Before completing all the mods Mark suggests,
Europeans might wait with removing the 100 ohm resistors till
All the other mods are fine, fire ahead 100 percent with those,
perhaps replace the resistors with something in the order
of 220-390 ohms or even take out the T/R delay switch and
fit a two-pole rotary switch with facility to switch in either
100, 220 or 390 ohms as well as the open circuit position
(i.e. zero resistance)... Then, depending on the amount of
local RF, a suitable value could be chosen to prevent spurs
On the other hand you can always do what Mark suggests and
that is to wind back the Gain controls a little.
Paul Ormandy, New Zealand
These modifications are trivial to make --- rather than
desolder the surface mount components and risk heat damage
to surrounding components, the offending filters were "crushed
in place" by squeezing them with needlenose pliers to to remove
them. Loads easier than attempting to desolder. Should you
ever wish to revert, it is easy to desolder the remaining
end of each component, and to resolder in new surface mount
Don, Oregon, on hcdx list,
August 27, 2000
first modification is to correct for excessive signal loss
at frequencies below 2 MHz. The unit is advertised as covering
down to VLF, but its stock version has insertion losses ranging
from 5 dB at the top of the medium-wave band (1700 kHz) to more
than 30 dB of loss down at 530 kHz. By the time you get down to
the European longwave broadcast frequencies, there is so much
loss that you might as well be receiving on a dummy load. Removing
six high- pass filtering components - L5, L6, R27, L3, L4, R26
- totally corrected this problem.
Apparently the engineering people decided that this was going
to be a shortwave-only unit when the advertising department thought
that writing it up as having coverage down to VLF sounded nice
... clearly, somewhere along the line, there was a failure to
modification corrects for an inability, in some cases, to
obtain enough phase shift to produce nulls. If the phase adjustment
covered 0 to 180 degrees, then setting the reverse switch gives
us 180 to 360 degrees (also expressable as -180 to 0 degrees).
But what if the phase adjustment range at some frequencies is
only 0 to 120 degrees?
The inverted setting will be 180 to 300 degrees. If we have the
need for a shift of 150 degrees to obtain a given null, this condition
will not be producible. Judging by some of the medium-wave nulling
tests, lack of sufficient phase-shift range does appear to be
Luckily, there is a relatively simple solution:
Reversing the antenna inputs so that what had been the "main"
antenna during a non-working null scenario becomes the "auxiliary"
and what had been the "auxiliary" becomes the "main". In the example
above, we'd change the +150 required shift to -150 degrees, which
is equal to +210 degrees (-150+360). This is now within the window
of possible adjustments. As long as the adjustment range is better
than 90 degrees, it will be possible to cover all required nulls
if the channels are made "swappable". Tests performed still show
a few cases where a null occurs at either the extreme right or
left setting of the phase shift control, but at least a null can
be produced with the antennas connected one way or the other.
A double-pole / double-throw (DPDT) "swap switch" was added to
facilitate full null coverage. I mounted it on the rear of the
unit because of limited space on the front panel. Two lines were
cut to allow swap switch use. The first of these was the lead
from the SW4B arm to the R20 pot (auxiliary level). The second
cut was in the line from C8 to the R9 pot (main level). With the
DPDT switch set to "normal", the switch completes the previously-wired
paths: SW4B arm to R20; C8 to R9. In its "swapped" position, the
SW4B arm gets connected to R9 and C8 gets connected to R20.
A couple of minutes spent studying the schematic and board layout
should make it obvious how to install this modification.
Conceivably increasing the value of the phase shift circuit component
C12 could also increase the phase-shifting range. I'm thinking
of putting a varactor circuit in the box in place of SW2A, C12,
and C13. The potentiometer installed (in lieu of the SW2 high
/ low frequency range switch) to adjust the varactor capacitance
could act as a "vernier" for nailing down deeper nulls.
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".