Timewave ANC4 Noise Filter

These days the amateur bands are becoming increasingly plagued by interference from all manner of sources, from computers to energy saving light bulbs! In some cases the noise can show up as S9 or more making the bands(s) completely unusable. This is what happened at my station about four years ago! One day I switched on 15 metres and there was S9 of noise! Over the following year other noise sources cropped up on other bands also. I tried a DSP noise reduction unit with little success. I decided the best thing to do would be to try a noise canceller which stops the noise before it gets into the radio. There are a few on the market and I opted for the JPS ANC 4 now manufactured by Timewave.

How Does it work?

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The block diagram of the filter is shown above. Basically the unit works by picking up the local noise on a small noise antenna. The noise is amplified and combined with the noise source coming from the main antenna. When the two noise sources are exactly out of phase by 180 degrees or so the noise is cancelled. The wanted signal remains as it is not picked up by the small noise antenna, only the main antenna. You can use either the telescopic whip supplied with the unit or a remote external noise antenna such as a very short dipole (2 feet overall length).

How Effective is it?

This can be a very effective unit and I have found it can null out noise sources from S9 to virtually nothing. However, it is absolutely crucial to get the noise antenna as close to the noise source as possible. For instance my neighbour's house kicks out some noise from the switch mode PSU on his TV. By placing the noise antenna against the wall adjoining his house I can null out the noise quite effectively. If you cannot get the noise antenna close enough to the noise source to give a reasonable amount of signal, the unit is much less effective, and sometimes useless! Be aware also if you have more than one noise source (such as here where I have crap coming out of both neighbouring houses), it will be extremely difficult  to phase out both sources of noise.

The unit seems to be quite effective on all bands up to and including 50MHz. I have found it particularly effective on 160/80 meters.

These filters are fairly expensive (~200 UK pounds) and I would only recommend buying one if you can be sure where the noise is coming from and that you can get a noise antenna say within about 15 feet of the source.