MFJ-1025
A new toy in the shack via the Ontario Swapshop.
The MFJ 1025 is a two antenna phasing unit that works by phasing the inputs of two antennas to either peak or null a signal. The directional characreristcs of phasing the antennas is solely based upon the charecteristics of each antenna i.e. gain, polarity and radiation pattern. Tight spacing of the two antennas allows peaking or nulling of local siganls or noises, further spacing allows peaking/nulling of more distant sources.
I have had great success nulling local powerline and trolleybus noise with the unit, making some of the shortwave broadcast bands listenable once again. Vancouver electric buses run on a 600v system which creates considerable RFI but particularly in the downtown core where numerous lines crisscross. The noise itself is only heard as buses travel nearby and is more than likely generated by the buses own motor. Frequencies in the 40m to 60m bands are most susceptible to this noise, though the noise can be heard on most bands. Rain or heavey moisture in the air can increase the gain of this type of noise considerably.
The 1025 has also allowed me to reduce a new noise source which has only recently popped up on the dial. Spread out between 1.5 mhz and 18 mhz, this odd warbling noise popped up exactly every 67 khz. Some research has shown it to possibly be a touch lamp of some kind. It seems that this is a much more distant noise source as the point of nulling is very narrow and takes a little fiddling on the MFJ. The successfulness of noise reduction on the 1025 is based upon matching the antennas. Antennas with similar polarity and gain will have the most success. A small loop can be handy to use as the second auxillary ‘noise’ antenna as its polarity can be easily changed to match that of the main antenna.
Right now I have had great success phasing my Sony AN-1 vertical with the AN LP-1 loop, though I have also phased my longwire with the loop also. I’d love to get my hands on another outdoor active vertical antenna like the AN-1 and phase them together. So if you know anybody with a similar active antenna unit for sale drop us a line here at va7dxc hq. The overall goal is to create a cheap and cheerful version the DX Engineering dual vertical phased rx array which retails for about $1000! I’m going to try and do it for about $200.
The 1025 also accepts a tx antenna antenna as the main antenna and includes and rf sense and/or switch which disengages and grounds the second rx antenna during transmit. If and when I do get around to getting on the hf bands here the MFJ 1025 will go a long way towards at least helping me hear the stations that I would like to work.
