X-Phase QRM Eliminator

I bought an X-Phase QRM eliminator a while back, tried it out with a receiver and was quite impressed with its performance. It’s only recently that I’ve connected it to a transceiver because without care it is easy to damage the unit when transmitting.

QRM eliminators have been around for many years. I was recently looking at an old Practical Wireless from 1989 and S.E.M. were selling one then in the adverts at the back of the magazine. (And, yes, we used dots in a.b.b.r.e.v.i.a.t.i.o.n.s. back then). If you were to be picky you might say it should be called a QRN eliminator, but it isn’t. I quite like the idea of an actual QRM eliminator though I’m not sure how you could implement it. 

Scan 9 May 2020 at 14 34

A QRM eliminator works like this: signals from the main aerial are mixed with signals from a noise aerial. The signals from the noise aerial can be shifted in phase. The idea being that you mix the main signal with the noise signal 180º out of phase. If the signals are the same you’ll just get a zero signal. But if the main signal comprises a good signal and some noise signals and the noise signal is predominantly the noise signals, you’ll end up with just the good signal. Of course, to make this work you need to be able to make the noise signals from the main and noise aerials be the same amplitude so the QRM eliminator has controls to adjust the gain of each. As you want the signals to be 180º out of phase there is also a control to adjust the phase.

Front of QRM Eliminator

The three blue knobs in the photo are these controls.

There are several QRM eliminators on the market. I got mine from Poland on eBay from the seller urbania2. The unit is solidly built in a neat aluminium box with pleasant to use control knobs and strong connexions on the back. 

The instructions are in a quaint mixture of Polish and English but I found them understandable enough as a circuit diagram is included.

I have done some quick tests on 20m with the unit and it seems to be able to reduce the background noise by about 3 S-points as shown on my TS590S transceiver. I also made some measurements using received FT8 signals. This showed an increase of about 4dB in the signal strength of CQ signals as reported by JTDX over 15 minutes with the QRM eliminator being on each even minute and off each odd minute. None of this testing was particularly scientific though. I was using a 4m length of loudspeaker wire as the noise aerial, just lying on the floor of the shack.

Eliminator connexions to TS590S

I mentioned that it’s easy to damage the unit when transmitting. It has three wires. Red and black are for the DC supply, and the yellow wire is for the PTT. When grounded the eliminator passes the main signal straight through avoiding the damage.

This Is how I connected my TS590S. The EXT-AT connector on the TS590S provides a nominal 13.8V DC. So I used pins 1 and 6 to power the Eliminator. I got the EXT-AT plug from an eBay supplier asia_uk.

TS590S EXT AT Connection

The remote connector on the TS590S isn’t particularly well documented, but connecting the yellow wire from the Eliminator to pin 4 works, but only if menu 53 on the TS590S is set to 2. Pin 2 on the remote connector, the common terminal needs to be grounded so I connected it to pin 3 on the EXT-AT seeing it was spare. I got the required 7-pin DIN plug from RS Components.

TS590S Remote Pinouts

3 Replies to “X-Phase QRM Eliminator”

  1. Interesting. I have my eye on this particular unit. I’m a shortwave listener and not an amateur/ham radio operator. So I have my portable radios, my loop antenna and that’s it. Is it possible to power this device from the mains? I gather if you’re a ham you can connect it up to one of your devices and power it through there. I don’t see anyway of powering it from the mains though? These eliminators don’t appear to be designed for folks who aren’t amateur radio operators. Maybe I’m wrong. Thanks for your help.

    1. The eliminator uses 12 – 13.8V DC. So you need a power supply. You can get ‘wall warts’ that will provide 12V. They cost very little. They plug into the mains and have a DC plug on the end. This DC plug would need to be cut off and the wires attached to the 4-pin plug that comes with the eliminator. Wall warts can be quite noisy at radio frequencies so a better but more bulky choice is to get a linear bench power supply. But these are more expensive. A bench supply would have the advantage that the appropriate wires from the eliminator 4-pin plug could be attached directly. Usually they are just held on with a screwed down washer. Another choice is to use a 12V lead-acid gel battery, but you would need some way of charging it.

      But always play safe. You don’t want to survive the virus and then electrocute or burn yourself.

      I suggest you search for “bench power supply”, or “13.8V power supply” in your favourite online store. The eliminator uses a low current so you don’t need a beefy power supply.

      Have fun with the SWLing!

      1. That’s great information. Thank you. I can see that this could be a relatively expensive experiment if it doesn’t work out! Potentially adding more noise from the mains doesn’t sound good. Certainly whenever I’ve used the provided power supply with my radios it has added noise. A bench supply sounds good but it all adds to the cost. I just have a nice bedroom space and something like that wouldn’t go down well! Maybe if I get a man cave. I think I’ll leave it for now. Thanks again.

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