QRM eliminator

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Andrew (grayhat)
Posts: 274
Joined: Sat May 28, 2022 5:56 am
Location: JN63pn

QRM eliminator

Post by Andrew (grayhat) »

let' s start from an example of the kind of unit I'm referring to

https://www.amazon.com/Eliminator-X-Pha ... B09B37KQ12

but there are several others using the same approach, a connection to our antenna and a connection to a so-callled "aux antenna", "noise antenna" or "noise probe", the unit works by allowing to adjust the level of both antenna so that it will be almost equal, and then allowing to shift the phase of the "noise antenna" signal to 180 degrees, so totally cancelling the noise

Now, the main problem with such unit is that, to properly work, it needs a "noise antenna" presenting the same (or better) noise than the regular antenna, this is often an issue and causes less than optimal performance from the noise canceller

Here's a solution, nothing new, it was widely used in a past as a regular antenna, but nowadays isn't viable, due to the noise generated by various sources... but the noise is exactly what we need for our "noise antenna" so ...

The idea is using the AC mains as an antenna, again, not new, but works, here's how to set it up

Pick two 1KpF capacitors rated for, at least, 1KV and two 150 Ohm resistors (small ones will do), now pick a wall plug, open it and connect a capacitor to each (phase and neutral) post, solder a resistor to the other end of each capacitor and finally, solder the other end of the two resistors together; now pick a lenght of coax cable, solder the center conductor to the joint between the two resistors and connect the braid to the ground post of the plug, ensure to use insulating tape and heatshrink to insulate the connection and close the plug; connect a suitable RF connector (e.g. a BNC) to the other end of the coax coming from the plug

now we're ready, connect the cable we just built to thr noise antenna socket of the "qrm eliminator", connect the regular antenna to the other socket and connect the wall plug to a ... mains AC socket

Now, power on the "noise eliminator", power on your receiver, tune around and adjust the "noise eliminator" to cancel whatever interfering noise

that's it
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