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Having 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.
Background: 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.
On the other hand, at one of my
locations I have a very harsh RF environment, consisting of:
A) A Loran C navigational beacon at
100 kHz, 200kW, 4,500 meters away and visible.
B) An NDB at 399 khz, 100w, 1,500
meters away, not visible.
C) A shore-to-sea communications station on 1695
kHz, 10kW, 1,500 meters away, not visible.
Needless 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.
My impression is that the amplifier supplied with
the MFJ-1025 is not on par. 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.
For comparison, I purchased the APU-100 phaser from
Wellbrook Communications. 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.
An added 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.
My conclusion 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).
---From the world's northernmost DX-er--- 71°N, 29°E Bjarne Mjelde P.O.Box 58 N-9980 Berlevåg, Norway Receivers: AR7030+, KWZ-30 |