Accessibility Evaluation of MFJ 1026 Noise cancellation Unit.
By Kelvin Marsh M0AID
Recently, there was an interesting thread on the active elements reflector, regarding local electrical noise sources. These days, many radio amateurs live in electrically noisy locations, often with close neighbours in a modern housing estate.
Potentially, these local noise sources can make it very difficult, if not impossible, for radio amateurs to continue in the hobby. Very often, the electrical interference is so bad it literally overwhelms the weak incoming signals amateur radio operators strive to hear.
I was interested to learn that several sighted radio amateurs used noise cancelling units. Several of these units had been around for many years, but had been discontinued. Checking with the various suppliers, I found the MFJ 1026 was the modern equivalent, and was widely available.
Firstly, the unit is quite expensive. I have no doubt the manufacturer has done their very best to keep the costs down, but the MFJ 1026 is a significant investment at around £200 GBP. Therefore, I felt it was imperative to check the MFJ 1026 is accessible for a blind operator.
Reading the Manual, my first concern was how to handle the MFJ 1026 transmit requirements. Usually, the MFJ 1026 is connected between the radio and the antenna. This means it can receive incoming signals directly from the antenna, but has to potentially handle several hundred Watts of outgoing RF power when the operator is transmitting. The MFJ 1026 has some features to switch it to automatic bypass, but the Manual is at pains to point out, this method is not fool proof and is not recommended. It is suggested the MFJ 1026 is also connected to the radios PTT circuitry, and is thus switched to bypass, when RF power is applied. This means an additional cable must be fitted, and the specification will depend on the type of radio being used. The additional PTT control line may need to be added to the order, as fabricating the necessary cable could be difficult for an amateur with low vision.
Fortunately, my own radio gives access to incoming signals via coaxial links at the rear. I was able to use the appropriate connection and route the RX signal through the MFJ 1026, avoiding placing the unit in the path of out-going RF.
The MFJ 1026 works by receiving signals on two separate antennas. The noise is brought in by the auxiliary antenna and this is used to cancel the noise on the main antenna. The tricky part of the operation for a blind operator, is to balance the noise signal on both antennas. Usually, a sighted operator will use the radios signal strength meter, but I found it was easier for me to match the balance by ear. I found the best method was to turn the main antenna gain to maximum, so you hear the incoming signal and noise at full strength. I then made a mental note of the noise volume, and turned the main antenna gain completely down. I then brought up the noise on the auxiliary antenna to the same level. The final step involves careful adjustment of the Phase Delay, until the noise is effectively removed.
At this point it is worth mentioning, I had good success using the MFJ 1026 internal whip as the auxiliary antenna. This was very effective at picking up a local noise source . Thus, the main antenna would receive both the radio signal and the noise, whilst the whip antenna would only pick up the noise. The unit can also be used with an external auxiliary antenna, but during my limited testing I found I did not have much success in reducing noises from further afield.
Fortunately, I do not have much interfering electrical noise at my QTH. During the test period, the only local noises I found were a couple of spot frequencies on 15m, when my beam was turned towards the south.
You will now hear a recording of Z81D in South Sudan. The signal is very weak, and without the MFJ 1026, would have been affected by the local noise. Either side of the frequency was in fact clear of noise, but Z81D was just on a bad spot! During the recording, you will hear me calling the station myself, and Z81D making three QSOs. Although these are faint they are without interference, but as he is exchanging signal reports with each station, I briefly turn off the MFJ 1026 and you can hear the rasping interference for a few seconds each time. Whilst these signals are on the limit, you can hear that in this instance, the reception would be virtually impossible without noise cancellation.
Next is a recorded demo of the MFJ 1026 in action. I use the unit to eliminate an electrically generated noise from the 80m band