Home » Radio » Radio Frequency Interference » Assembling My RA0SMS X-Phase QRM Eliminator

Assembling My RA0SMS X-Phase QRM Eliminator

assembling RA0SMS X-Phase

I finally got around to assembling my RA0SMS X-Phase QRM Eliminator kit which arrived from Russia last month. Here’s the story.

The basic circuit idea of the X-Phase has been around for decades. You will find many folks have produced these units, including a variety of kits. I bought my kit from RA0SMS on E-Bay for US$21. After a few days of use, I can confirm that the circuit works well. Not as well as an ANC-4, but pretty good for the price.

In this article, I will talk about the circuit itself. If you want to follow the schematic you will find it here.

X-Phase adds signals from two antennas. Along the way, you can adjust the amplitude of signals from each antenna separately, and also change the phase with which one of the antennas is mixed with the other. Normally, you would have signals from your main antenna and a separate noise probe, but you can add signals from any two antennas, including wideband loops.

Your circuit board contains three potentiometers. Two of these adjust the amplitude of each antenna. One of these adjusts the phase from the secondary antenna before it is mixed. The gain pots are actually just variable attenuators to reduce the signal entering each of two FET amplifiers. The circuit runs off 12 VDC.

Two relays let you use the device with a ham transmitter. Normally, when powered off, the main antenna goes through normally closed contacts direct to the output. When power is applied, the relays switch the signals through the X-Phase circuit. A PTT input is available to switch the circuit when transmitting. (X-Phase does not have RF sensing such as used in the ANC-4.

Assembling My RA0SMS X-Phase – Boxing it Up

Of course, I 3D printed my own box for this project, as shown above. My PCB is held in place by the potentiometers at the front, and a pair of screws with threaded inserts at the back. These also double as ground points for the antennas and power supply. My box took more than six hours to print and cost $3 worth of plastic filament.

You will notice the power jack to left in the picture. I have settled on barrel connector adaptors designed for CCTV installations for many of my projects. These are available male and female, really inexpensive and easy to glue down in a plastic box. Because they use the standard 2.1×5.5 millimeter form factor, you can often use junk box power cubes, or just attach to another power supply using the male adaptor.

One comment

  1. Zaba says:

    Happy Easter, John!

    My first posting was in October regarding PEX-loops. I subscribed to your blog, while almost all
    of your technical subjects are very close to my interests. I would badly need an X-phase eliminator for a few of my operating sites. Actually I have PCB of a DK9NL v.1.0 version, and I see that the schematic (dated 12.5.2001) is almost identical to yours (the RA0-version having just the protection diodes doubled, two in series).

    You may have a more precise analysis from your SPICE-model, but if I look at the schematic it appears as if the phase adjustment is not able to make the full 360 degree circle. Also probably phase and amplitude are not independent, so optimization for each instant is an iterative process (multiple subsequent “visits” to the potentiometers). I guess, one marked improvement would be to switch in a couple of delay line options in the Ant 2 line reference path, trying to reach the full 360 degree phase range. It would be best to have these lines terminated in their nominal impedance to avoid amplitude/phase-variation when switching the length….

    Cheers/73, Zaba OH1ZAA

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.