In a previous post I did a review on the X-phase QRM eliminator. I found out that the antenna for receiving QRM, the auxiliary or secondary antenna, holds the key to optimum performance of the QRM eliminator. A single wire along a shelf in your shack is, for what I tested, 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 was a 13m (31 ft) tall vertical. It’s elevated 8m (23 ft) from the ground and has several sloping radials. It’s fed through a CG-3000 remote automatic tuner, that sits at the base of the vertical. This antenna setup allows me to work on all HF bands. The downside… it picks up loads of man-made noise.
It should perform better than this
The QRM eliminator manual says 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 auxiliary antenna. For eliminating the noise from my next door neighbor’s solar panel inverters, it was effective, but not to my satisfactory. It could perform better than this.
Increasing the signal level on the aux antenna
The QRM eliminator enables you to adjust the signal levels 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 as you adjust the phase angle. But if the aux antenna does not produce enough signal strength, the QRM eliminator cannot eliminate all of the QRM.
Man-made noise is mostly vertically polarized
Presuming that bringing the aux antenne outside the shack, would increase 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 a new aux antenna.
Increase signal level and bandwith
Having some aluminium tubes left form earlier antenna projects, I installed a 2.7m (9 ft) long vertical whip on the roof, close to the neighbour’s solar panel inverters. This turned out to work better than the wire inside the shack. Especially on the higher HF bands, I was able to cancel out most of the QRM. But its performance on 30 meter to160 meter band was still not great. I could double the length of the whip to cover the longer wavelengths, but that would negatively affect the shorter wavelengths bands
To get maximum performance on all HF bands, I needed to:
- Increase the overall signal level from the aux antenna.
- Increase the bandwith so it produces enough signal on all HF bands.
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 HF reception. One of the antennas I wanted to experiment with, was a Miniwhip. This is an active antenna designed by PA0RDT which covers a large part 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…
Sounded like the ideal aux antenna
That sounded like the ideal aux antenna for a QRM eliminator! I scavenged eBay.com and ordered a DIY Miniwhip kit from RA0SMS Anton. A week later, I received the PCB and power insert. Built the PCB into a 20 cm (9 inch) PVC tube. Metal has a disturbing effect on a Miniwhip, so I mounted it on a 2.5m (8 ft) fiber glass mast on the roof, close to the neighbor’s solar panel installation. Connected the ground terminal on the power insert to my station ground, several 3n (9ft) long copper tubes 3m (9 ft) into the swampy wet soil here. Ready to go!
It picks up loads of QRM
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. On 20 meter band, I am able to cancel out the solar panel S9+10 dB noise to near zero. Watch this short clip:
To get the best out of a QRM eliminator over a large part of HF, the Miniwhip is one of the best options for an auxiliary antenna. Its size, 20cm (8 inch), allows you to mount it anywhere you like, close to the main noise source. You can use cheap RG-58 coax cable, or even TV coax and use a power feed unit to supply current to it via the coax cable.
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 meter to 10 meter band. Only downside of the Miniwhip is that on 10 meter band it performs not as good as other bands. You might want to consider adding a quarter wave groundplane or dipole for 10 meter and antenna switch, so you can switch between aux antennas.