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Author Topic: Subtracting One Signal from Another?  (Read 413 times)
KC2NLT
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Posts: 91




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« on: November 06, 2017, 09:59:56 PM »

I was thinking about how active noise reduction/cancellation headphones work. The technology exists in many cell phones, too.

These headphones usually have small mics on the outside that pick up the ambient noise and then create an inverse of that noise inside the headphones. This results in noise reduction or noise cancellation, silence. 

Borrowing from that concept, I was thinking if it's at all possible to point a directional antenna at a station that is transmitting interfering unwanted signals on the same frequency or a nearby frequency and then pointing another directional antenna at the station that is transmitting the desired signal and then simply subtracting the unwanted signal from the desired signal to get a cleaner and clearer signal from the desired station.

Is there a device out there that currently does that?

Could the same be done with locally transmitted signals, in the sense that one can subtract the unwanted local signals picked up using an omni antenna from the signal received by a directional antenna that is aimed at a desired station?
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VA2FSQ
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Posts: 569




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« Reply #1 on: November 06, 2017, 11:01:39 PM »

Hi
These devices exist.  I have the NCC1
Here's a previous thread...
https://www.eham.net/ehamforum/smf/index.php/topic,87548.0.html
73
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VA2FSQ
N3QE
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Posts: 4875




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« Reply #2 on: November 07, 2017, 03:18:19 AM »

Yes, with phasing of two antennas it is very possible to put a QRM'ing signal "in a null". As a practical matter this might be dropping the QRM by 40dB-60dB.

http://static.dxengineering.com/pdf/NCC-1-Rev5d.pdf
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