QRM Eliminator

[@lottapossum1812]

Thank you so much for this scope analysis, Mr. Chris! This is the *only* scope dive into this cool little QRM buster circuit that I could find. My little black box arrives today and I'm going after the rotten QRM around my shack. I think I get now why a simple 180 degree inverting amplifier isn't used on the noise antenna's signal. The noise signal arrives at each of the two antennas at different instants and will be slightly out of phase with each other, because of the physical separation of the antennas and the directions of the incoming desired and QRM signals. So the actual phasing has to be adjustable at the receiver to "lock out" the QRM, because every OP's antenna setup is different. Does this sound right? And you demonstrated (and showed your formulas and calculations!) how a simple circuit can provide the phase shifts. Thanks to you, I *finally* get this. I think. Most excellent!

[@aerofart]

After watching countless videos of QRM Eliminator demonstrations by people who don’t have a clue about tuning these devices, it is nice to see someone putting actual signals on an oscilloscope like you’ve done here. I also like the XY display, and would also suggest you try adding a math channel that sums the two signal channels. This way you can get real voltage levels and won’t need to switch to the XY mode and back. Well done.

[@ke6chris]

Thank you

[@FrozenDoberman]

One of the main strongest QRM sources is 50 or 60 Hz power line buzz noise. This is most effectively heard using wide AM on any sensitive radio. RF phase cancellation units provide the deepest noise null on a single interference source that has a fixed degree phase value. The signal noise source is a function of its frequency, distance, and strength. The interference pickup antenna will often need more gain than the DX antenna. When both signals are 180 degrees out of phase with equal or near equal strength, a phase null occurs. Wanted DX signals are not usually nulled because it is unlikely they will have the same phase signature as the unwanted phase signature. There are lots of amplitude and phase combinations over 360 degrees.

[@docfoot316]

Liked seeing what was going happening with the phasing on the scope , Many thanks

[@kirkp_nextguitar]

QRM usually means interference from undesired transmissions in the same frequency band you are tuned to. Your device seems to be intended to null out of band interference. It might be useful if you are trying to operate very close to an strong out of band transmitter that is overloading your receiver, such as a commercial broadcast tower, but that’s not the typical case.

[@ke6chris]

Thanks for the comment. I added a ban pass filter to the circuit.

[@so0749]

Excellent video. Very impressive. What happen if we have phase volume as it is but no volume controls for pre-amps (both anntena imputs). Instead, we put a volume at the point we mix two signals to change the ration. It may reduce the effort of tuning. What do you think? Thank you.

[@ke6chris]

That's a good experiment. Chris

[@FrozenDoberman]

Thanks for the technical explanation. Does anyone know why the QRM Eliminator tops out at ~ 30 MHz? Is this a function of the active internal amp? Perhaps some oscilloscope dual wave tests will reveal the practical upper frequency limit coverage.

[@francodegregorio1957]

Ok ottima spiegazione del funzionamento, ma in pratica risulta difficile trovarsi in queste condizioni, il rumore generato da varie sorgenti di rumore stesso non riescono a sfasarsi correttamente con il segnale presente da Ricevere utile da ascoltare.

[@ke6chris]

True

[@karlmartell9279]

Are the QRM-Gloves really working?