The JPS ANC-4 Antenna Noise Cancellers claim to reduce unwanted noise by typically 40db or greater up to 80MHz! Do they really work? If they are that good, why doesn’t everyone use them?

Here are my experiences with its use on 6m to combat QRM from the local TV on 48.250.

There are worthwhile benefits but installation is critical and constant attention and tuning is required.

The unit is similar in principle to a Noise Cancelling microphone. It takes a sample of noise, amplifies it and adds it to the signal from the main antenna 180degrees out of phase which results in cancellation of the noise. However, for the ANC-4, this is done with rf not audio frequencies.

There is no single performance figure that describes its benefits because it changes all the time. In some cases, it is brilliant, in other cases it has a small effect only. In my case, here’s what I observed:

• On average, it has reduced noise by 12 to 15 db
• The best I have experienced is a reduction of 40db with the antenna to the west. (As luck has it, this is towards South America)
• The worst is 0db to the north-east

One of the nicest operating features is that I can eliminate many of the spots when I’m tuning around the band looking for beacons and DX stations. It used to drive me crazy stopping every couple of KHz to check if I’m hearing a spot from the TV QRM or whether it really is DX.

This has to be done correctly

• Install a good noise antenna
• It should be an outside antenna if possible.
• It should be located so it picks up as much noise and as little signal as possible. That is, it should have a high Noise/Signal ratio. Mine is a dipole taped to an exterior wall that faces the TV TX and is shielded from the North which is where most of my signals come from.
• It should be the same polarisation as the main antenna.
• Reduce noise pickup on the feedline
• Use a balun if necessary
• If possible, shield the feedline. (I ran mine very close to the underside of the house’s metal roof.)
• The noise gain should be adequate
• Turn off your preamp or reduce its gain to the minimum necessary.
• If the main antenna is large and captures a lot of noise, the noise antenna will have to be larger.

It pays to be an octopus with 8 hands to operate. For every change in operating variable, you will have to adjust Phase Range, Phase pot, Noise Gain and do it several times to obtain the best null. If you have installed it correctly and adjusted it correctly, you should be able to get sharp nulls on both the Phase pot and the Noise Gain adjustment.

You will probably have to go through this repetitive adjustment procedure whenever:

• You rotate your beam
• The noise source changes in amplitude or in nature (this happens all the time with video QRM)

Yes, it is worthwhile and I would buy one again for $190US.

But it is not the best solution for my particular problem. I would choose the other solutions every time in favour of the ANC-4. The other solutions for my environment were:

• Using vertical polarisation (the TV is horizontally polarised) which is probably worth about 40db of noise reduction.
• Nulling out the noise using sharp pattern beam antennas. My close spaced 5el beams give 3 very sharp and very deep nulls. But of course, you have to live with the direction not quite being optimum.

These two factors can give me a fairly quiet band with only S4 noise. I really don’t have to use the Noise Canceller but it is nice just to be able to reduce that last bit of noise.

Thanks to Neil G0JHC and Geoff GJ4ICD for suggestions and encouragement for tackling the noise problems.

Alan Isaachsen, 3C5I.