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Worst Case Wideband RFI Reduction

worst case wideband rfi

All 4 of my test units attacked worst case wideband RFI successfully, but the performance of the cheap X-Phase really blew me away!

I thought we should start my noise reduction comparison tests at the heavy end of things. My worst case wideband RFI comes from poorly installed halogen lights in a nearby neighbor’s kitchen. When doing kitchen renovations, their incompetent electrician ignored the CSA approved 10 foot wiring harness for three lights, and did his own thing with sixty feet of #18 wire. As a result, the voltage drop across this circuit drives the switch-mode power supply crazy.

As a result, I have to live with wideband interference across several bands. Worst case is 11-12 MHz getting swamped with S6 or -100 dBm RFI. As you can see on the left, this includes 50 kHz noise peaks from the SMPS free running oscillator. Embedded in the interference you will also find a rich spectrum of 120 Hz harmonics. Neighborhood RFI doesn’t get much worse than this.

Shown above, clearly labelled, are my results from testing four noise reduction devices over the same hour and frequency band. To make this truly a worst case wideband RFI reduction test, I chose two wideband E-field antennas. I created these by putting my LZ1AQ AAA-1C wideband loops into vertical dipole (voltage gain) mode. My Main antenna is about 250 feet east of the offending kitchen. My Auxiliary antenna is 350 feet east of the noise.

As you know, most RFI from household wiring is vertically polarized. So, my vertically polarized E-field antennas are highly susceptible to this kind of interference. Thus, my description of “worst case”. (Magnetic loops in the same location are less susceptible to local RFI.)

Results were quite surprising.

Worst Case Wideband RFI Reduction Results

Amazingly, my best results came from both the cheapest and most expensive equipment. Best was the high-end DX Engineering NCC-1 Receive Antenna Phasing Controller. It reduced the noise floor by around 28-30 dB across a 600 kHz swath. But second best – and this blew me away – was the $21 RA0SMS X-Phase QRM Eliminator. Noise reduction with this little circuit was around 25 dB.

Not far behind, though were the MFJ-1026 and ANC-4 with similar noise reductions of 15-20 dB. However, these devices tended to peak the reduction across 200 kHz swath, requiring more frequent adjustment.

In all cases, signals were maintained within 6 dB when the units were switched in and out. In all cases, performance was reliable and repeatable.

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