MFJ-1025, go for APU-100
By Bjarne Mjelde
hcdx list, July 19, 1999
used the MFJ-1025 (modified) phaser for some time on MW, I
thought I'd send you a short note on a subject that hasn't been
much focused on by the reviews I have read.
No longer sold
Wellbrook has stopped the production of the APU-100 phaser.
If lucky, you may find a used copy.
I live in a region where in many instances only atmospheric or
galactic noise is of concern. Thus, I can use extremely
sensitive equipment when listening.
the other hand, at one of my locations I have a very harsh RF
environment, consisting of:
A Loran C navigational beacon at 100 kHz, 200kW, 4,500 meters
away and visible.
An NDB at 399 khz, 100w, 1,500 meters away, not visible.
shore-to-sea communications station on 1695 kHz, 10kW, 1,500 meters
away, not visible.
to say, these RF sources and the Loran C station in particular
require well-designed and well-built antennas, ground systems,
feedlines and listening equipment incl. amplifiers etc.
I use two beverages of 100, resp. 200 meters, grounded and transformed
to a 50 ohm coaxial feedline.
is that the amplifier supplied with the MFJ-1025 is not on
During low signal level periods the amplifier clearly produces
noise, especially from the AUX antenna input.
During periods of high signal levels, such as nighttime, the effect
is not as profound, but still noticeable.
My theory is that the relatively simple amplifier is the reason
why this effect appear.
comparison, I purchased the APU-100 phaser from Wellbrook
This phaser uses a push-pull amplifier with transformer feedback
transistors and pulls out 5dB extra gain in addition to the gain
used for the phasing unit.
This amp has a TOIP of +40dBm and a SOIP of +72dBm and produces
no noise at all in my environment.
In fact it is totally transparent, in that when the phaser isn't
used, you won't notice the phaser.
While on the MFJ-1025, reception seem to degrade marginally as
long as the phaser isn't switched off.
benefit to the APU-100 phaser is that it seems to produce
deeper nulls than the MFJ-1025, although I have tested both phasers
with only a limited array of antennas.
is that anyone who is considering buying an antenna phaser
should seriously consider the APU-100. At least this is
true for European DX-ers (I have heard that Wellbrook for some
reason declines to export to the US).