In a previous post I did a review on the X-phase QRM eliminator. I quickly found out that the antenna for receiving QRM, the auxiliary or secondary antenna, holds the key to maximum performance of the QRM eliminator. A single wire along a shelf in your shack is, for what I tested, clearly not enough. There is one specific antenna that does an amazing job.
Picks up loads of QRM
First of all I need to explain about my antenna setup. My main antenna is a 13 meter (31 ft) tall vertical. It’s elevated 8 meters (23 ft) from the ground and has several sloping radials, mostly two per band. It’s fed through a CG-3000 automatic remote tuner, that sits at the base of the vertical. This setup allows me to work on all HF bands, but also picks up loads of man-made noise.
It should perform better than this
When first installing the QRM eliminator, the manual stated that a single wire in your shack can do the job. That being said, I ran a 4 meter (17 ft) wire across the edge of the ceiling as an aux antenna. When trying to eliminate the noise from my next door neighbour’s solar panel inverters, it did a nice job, but not to my satisfactory. It should perform better than this.
Increasing the signal level on the aux antenna
The QRM eliminator enables you to adjust the signal level on both the main and aux antenna. When at the same level, the signal from the aux antenna will cancel out the signal from the main antenna, when adjusting the phase angle. But if the aux antenna does not produce enough signal strength, the QRM eliminator cannot eliminate the QRM.
Man-made noise is mostly vertically polarized
Presuming that bringing the aux antenne outside the shack, would increase the its signal level. The one antenna available outside is a dipole for 6 meter band, which sits at 10 meters (33 ft) above the ground. It is as close to the noise source, the neighbour’s solar panel inverters, as the wire that ran through the shack. It turned out that the dipole produced indeed more signal, so I was able to cancel out more of the QRM. But knowing man-made noise is mostly vertically polarized, I constructed e a new aux antenna.
Increase signal level and bandwith
Having some aluminium tubes left form earlier antenna projects, I installed a 2.7 meter (9 ft) long vertical whip on the roof, close to the solar panel inverters. This turned out to work quite well. Especially on the higher HF bands, I was able to cancel out most of the QRM. But its performance on 30 meter band to 160 meter band was still not to my satisfactory. But I realized doubling the length of the whip would negatively affect the higher HF bands. My two main goals:
- Increase the overall signal level from the aux antenna.
- Increase the bandwith so it produces enough signal on all HF bands.
To reach those two goals, I had to figure out what antenna performs better over a much larger bandwith, than a fixed length whip?
Good bandwith and sensitive to QRM
Few years ago, when the noise from the solar panels came banging in, I experimented with different antennas for reception on HF. One of the antennas I wanted to experiment with, was a Miniwhip. This is an active antenna designed by PA0RDT which covers a good part of HF. But other amateurs advised me not to use it, because a Miniwhip is very sensitive to QRM. Wait a minute, an antenna that has a good bandwith and is sensitive to QRM? That sounds like…
Sounds like the ideal aux antenna
That sounds like the ideal aux antenna for a QRM eliminator! I needed to get my hands on a Miniwhip, so I scavenged eBay.com. I ordered a PCB, with the power insert feed unit to supply current via coax, from RA0SMS Anton in Russia. Over a week later, I received the PCB and built it into a 20 cm (9 inch) PVC tube. I mounted it on a 2.5m (8 ft) fiber glass mast (metal has a negative effect on a Miniwhip) high on the roof, close near the solar panel installation. Connected the ground terminal on the power feed unit to a wire running to my HF ground, two copper tubes about 2.5 m (8 ft) into the wet soil (ground water level sits at average 1 meter (3.5 ft)). Ready to go!
It picks up loads of QRM
The result is very satisfying. The Miniwhip produces a lot more signal than any of the previous auxiliary antennas I used. It picks up loads of QRM, which was one of the two main goals. It also performs much better on the lower HF bands, let’s say below 10 MHz, than a passive whip. On 40 meter, 60 meter and 80 meter, I am able to cancel out much more QRM. Second goal achieved. The property of the Miniwhip as a being a QRM antenna is confirmed as well. For example, on 20 meter band, I am able to cancel out the solar panel S9+10 dB noise to near zero. Watch this short clip:
The Miniwhip is probably the best possible solution as an auxiliary antenna to get the best out of a QRM eliminator. Its size, 20 cm (8 inch), allows you to mount it anywhere you like, close to the main noise source. At least, as long as there are no metal objects within about half a meter (two feet). You can use cheap RG-58 coax cable and use a power feed unit to supply current to it via coax. Hence you can even use the Miniwhip to listen to all HF bands if your main antenna only covers a single band or for example, 20 to 10 meter band. Only downside of the Miniwhip is that on 10 meter band it performs not very good. So you might want to consider adding a quarter wave groundplane or vertical dipole for 10 meter and antenna switch, so you can switch between aux antennas. Which is also my next experiment, but not before solar activity picks up and “Ten” comes alive.