User Review by New Zealand DXer Steven Greenyer
After reading the review of the above unit in the September DX Times, I purchased the unit from MFJ Enterprises in the States. The total cost of the unit was NZ$243 including airmail of US$24. After ordering I noticed the price US$10 cheaper in the Universal Radio catalogue. MFJ responded promptly to my order with a note that the unit would be on back order for a few weeks and asking if I still required them to supply. The unit duly arrived by insured airmail with a full instruction booklet and circuit.
The unit has four knobs, a transmitter delay setting for ham use, main and auxiliary antenna gain knobs and a phase control. Three push buttons, on/off, hi/low frequency and normal/phase invert. The rear has the appropriate antenna connections. It is in a mat black case about 30mm x 150 x 200. Operation of the unit is well explained in the manual. After brief use I carried out part of the modifications recommended by Mark Connelly.
I use the unit under two operating conditions. At home, two antennas of 100 metres each both terminated and with baluns to coax feeders, one running North and the other East. With this set up good signal and noise cancelling is possible. Combining of signals from the two antennas does not appear to work as well and requires more experimentation.
At the Tiwai listening post there is a choice of several Beverage antennas varying from 300 to 600 metres in length. Here results fully came up to expectations in signal cancelling and addition. I carried out many tests and the best results are detailed. On 1530kHz National Radio in New Plymouth and the Wireless Station in Hastings both battle it out. While in some parts of New Zealand these may be looped out, down here they present a fairly similar signal path. With the unit it was possible to perfectly null one or the other simply by pushing the phase invert button. On South American signals using two antennas about 330 metres long and 6 degrees apart it was possible to get very good signal addition. By putting in phase the signals off the two antennas it was possible to get a four ‘S’ point increase in signal strength. This was constant with all the Latin signals down to about 1000kHz where the performance dropped off. The interesting point was that once set it was not necessary to alter the unit for changes in frequency. The unit was tried on both unterminated wires and those with a terminating resistor and matching balun to a coax feeder. It appeared to work well with both types, however on the higher frequencies the balun matching the antenna to a coax feeder and the receiver impedance is worth three ‘S’ points on it’s own. At lower frequencies i.e. 790kHz, there was a slight addition without the balun.
Conclusions: based on my observations – with shorter antennas around 100 metres, good nulling is possible of signals and local interference with varying degrees of signal addition, this may be due to my antennas rather than the unit. With longer antennas 300+ metres, very good nulls can be obtained along with very noticeable addition of signals above 1000kHz. The drop off below this is I expect due more to antenna characteristics than any problem with the unit. I am very pleased with the possibilities the unit offers especially for use with longer antennas. Any one who uses long antennas on mediumwave should seriously consider one of these units. No substantive tests on shortwave have been undertaken.