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RF noise cancelling at VHF frequencies.

Nov 20th 2012, 03:59

KM3F

Joined: Mar 6th 2008, 13:50
Total Topics: 0
Total Posts: 0
Would it be feasible to get a noise cancelling design to work on the same principle as the Time Wave ANC 4 using VHF construction methods?
This method uses a sampling antenna recieving the wideband noise and applying it 180 degrees out of phase for a null against the desired signal with the same noise, before the radio input..
I have an ANC 4 and works quite well up to 10 meters.
On 6 meters, not so well.
Would like to build one for 6 and 2 meters for power line noise control in weak signal work.
My beams point right into the noise area, very often.
Trying to get anything but known proven noise sources repaired is very tough if it is not very severe and outstanding.
Thanks.
KM3F
Nov 20th 2012, 12:12

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

The JPS ANC-4 is rated to work up to 80 MHz. I've also read a reputable report of it working well on 6M, though that page has since been taken down--as you know, the ANC-4 has been discontinued, so it can be quite a hassle to have a page up about something you can't buy anymore.

A null canceller typically won't help you if the beam points into the noise. Nor will it help you if there are multiple noise sources--you only get one null.

But, if you might experiment a sense antenna(s) that will move the null far off the desired beam headings using long runs of coax.

The shorter physical dimensions may allow a different way of implementing a null canceller on 2 meters. You may be able to implement the phase shifting by moving the sense antenna. The sense antenna could be a small Yagi with gain--amplitude matching could then be done with a resistive attenuator.

If you had a large property and the noise sources are close, it may be more practical to install widely spaced antennas and switch to the one that hears the best.

Zack Lau W1VT
ARRL Senior Lab Engineer

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