Skip MFJ-1025, go for APU-100 -- antenna special on hard-core-dx.com

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Skip MFJ-1025, go for APU-100

By Bjarne Mjelde
hcdx list, July 19, 1999

No longer sold
Wellbrook has stopped the production of the APU-100 phaser. If lucky, you may find a used copy.

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).