My New Körner 9:2 Antenna!

"Körner 9:2 Compact" Nine element band 2 beam

I had been considering replacing my trusty Triax FM5 for some time as I felt it was showing signs of age and was apparently starting to fail. Although I cannot be 100% certain, I had been wondering if the blue balun/connection box was starting to break down. They are notorious for this after all. The black connection boxes have not, so far, suffered the same fate, if you still have one of these.

Reception had been getting steadily worse for some time, but you can't always easily pinpoint exactly why this is. It could be general reception conditions at the coast. They are constantly variable at the best of times. There was also the possibility that water was getting into the coax or seeping inside the connection box. Reception could also have been worsened when I moved the FM5 from the mast at the bottom of the garden on to the rooftop. There were too many factors to be sure what was happening.

The fact is, something had been wrong for a year or so. The problems really began when the FM5 went on the rooftop. Dozens of continental stations just weren't there anymore. Then I noticed my local Belmont transmitter was a very weak and noisy shadow of its former self one day. We had been having heavy rain showers. That was when I first wondered if water had got inside the connection box. This situation lasted into the next day. Despite a general deterioration of reception, not everything was reduced in strength. Some stations in southern England were even slightly enhanced. So what was happening? I couldn't find any indications that Belmont had been on reduced power and, unfortunately for me, my fear of heights prevented me from climbing on to the roof to take a look at the antenna connections.

Along came the new "Körner 9:2 Compact" antenna during the middle of April, just in time for the sporadic E season. Firstly, I wanted to conduct some general listening tests on the garden to see how it performed, also to compare it with another FM5.

I assembled a makeshift mast on the garden and mounted the 9:2 some three metres above the ground and well away from nearby objects. WOW! I was blown away by the sheer number of continental signals coming in! I could hear lots of German transmitters at fully quieting, noise-free stereo levels. This was incredible! It was probably a foregone conclusion that the Körner 9:2 was going to superior to the FM5, but I expected something more modest, certainly nothing on this scale. I then began to feel convinced that there MUST be something wrong with my rooftop FM5.

Not only could I hear large numbers of continental transmitters, some of which I had not heard for a long time, but I was also aware how electrically quiet the FM band was when tuning on my Sony XDR-F1HD. The entire of band 2 was BLISSFULLY quiet. I could hear fully quieting signals in full stereo with ZERO BARS. I know that's not an accurate way to measure signal levels, but this sort of reception has only been experienced when on DX trips to quiet camp sites. The directivity of the 9:2 was also clearly superior than that of the FM5.

My next listening test was made using another Triax FM5 - not the one on the roof of course. I was expecting to hear a copy of the performance offered by the rooftop FM5, but with reduced signal strengths, but there was a shock. The garden FM5, while noticeably less sensitive and less directional than the 9:2, was still able to give me the same clean band, with the same continental stations I just heard on the 9:2, but with noticeably reduced signal strengths. This was a worry as it indicated that some of my problems with the rooftop FM5 might be due to excessive electrical noise and there was no guarantee that the noise would not be present on the 9:2 once it was on the roof. More tests were needed.

I will skip the details of the tests I carried out, but suffice to say they involved such things as measuring resistances and voltages which might have been getting into the mains earth, potential earth loops, etc. I also isolated the electricity supply to the property and ran the XDR-F1HD from a leisure battery/mains inverter while hooked up to the rooftop FM5. The noise was still there. So it was now becoming clearer that the noise was being received through the air. It is a broadband white noise type of interference which was not registering on the XDR-F1HD's display. It was of such a low level that it was effectively invisible, capable of blocking out the weaker signals. There are also a few other buzzes and PLT type clicks on some frequencies. Suddenly it is looking like this noise might have been responsible for the reduction in performance of the FM5 since it went to its rooftop location. The questions is, what to do now?

When the Körner 9:2 goes on the roof, hopefully this weekend, weather permitting, I hope I hear the same blissfully quiet band that I had when it was under test on the garden. Unfortunately, the reality may be that I will still have to contend with this noise. Further listening tests reveal that the noise is coming from an easterly direction, but there is still a sufficiently low level of background noise which is capable of blocking weak signals, no matter which direction I beam.

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The weekend came and the weather stayed dry. The FM5 was replaced by the Körner 9:2 and I owe a huge thanks to Andrew Webster who took to the roof and swapped the antennas over, completing the entire operation in around three hours.

Overall reception conditions hadn't been great throughout the day and had deteriorated further by the time the 9:2 was on the roof so I didn't expect to hear too much. Even as I type this on Monday morning I can report very poor scatter across band 2.

To begin with I looked for my regular continental transmitters, Lille, northern France at 343 km, Langenberg, western Germany at 505 km and Dudelange, Luxembourg at 573 km. These are receivable virtually all the time here but tend to be noisy during average conditions with occasional noise-free peaks. All of these exhibited noise free signals, peaking regularly via scatter. Other transmitters usually received on a daily basis but always noisy were either noise free or not far behind. These include Amiens (431 km), Rouen (426 km), Reims (516 km km), Chartres (531 km), Le Mans ( 599 km), Brest (604 km) and even Nantes (675 km). A good start!

The path to Germany is a difficult one as my interference comes from the east, but already I can detect signs of improvement with various transmitters in the Nordrhein-Westfalen, Hessen, Rheinland Pfalz and Saarland  regions coming in a little better. Here lies the problem though. The anticipated noise levels to the east are worse, as I was fearing. Worse than on the FM5 because of the extra gain of the 9:2, but as I expected, it is easier to steer away from it with the additional directivity provided by the 9:2. Indeed this is the more noticeable attribute and main selling point of the 9:2 beam. The directivity is considerably better than that of the FM5. Because the beamwidth is much narrower, I have had to re-evaluate some of my beam headings as suddenly they aren't quite where I had expected them to be! Two very clear improvements are the Lille transmitter on 88.7 and the Dudelange transmitter on 88.9, which were obscured by the splatter from local Belmont on 88.8. Now 88.7 and 88.9 are splatter-free!

The gain of the 9:2 is also a few dB up on that of the FM5 and has a smoother curve across band 2, whereas the FM5 drops off at the bottom of the band. In the technical specification the 9:2 peaks at 9.6 dBd at 103 MHz and goes no lower than 8.3 dBd at 88 MHz (The K6STI website quotes dBd figures as opposed to dBi which tends to be used by computer modelling software. There is about 2.15 dB difference between the two, but that's still very close). Compare 6.44 dBd and 5.23 dBd, respectively, on the FM5. The giant Körner 15:12 only reaches 9.56 dBd and 7.82 dBd at the same frequency points. Figures ex http://www.ham-radio.com/k6sti/korn1512.htm. Take note though, as stated on the Skywaves email lists, computer plots don't necessarily give a complete picture of the gain figures, but serve as a good guide.

The front-to-back ratio of the 9:2 is superb and I am able to lose many of those annoying signals which come in off the back of the beam, thus opening up numerous frequencies. At it's lowest figure there is a 27dB front-to-back ratio at either end of the band and this rises to the low 30 dBs, peaking at 35dB. I watched the signal bar meter on my Kenwood KT6040 tuner while I rotated 360 degrees while tuned to Belmont. Even 45 degrees off-beam I am able to see a good reduction in the signal, almost nulling it completely at 180 degrees. Belmont starts to break up and becomes noisy at this point, but remember, it is my nearest transmitter and is just too strong to null out completely. At least any propagation should easily get over the top of it now. All other signals are completely nullable here.

If I had ideal circumstances regarding planning and more space to operate larger antenna arrays I would probably have gone for the larger Körner 15:12, but after seeing the specification of the 9:2 I cannot see any meaningful difference, at least on paper, between the 9:2 and the 15:12. Just look at the size of the 9:2 though, it's only four inches longer then the FM5 !!!

It's a pity that the antenna isn't made anymore as I cannot recommend it highly enough. It combines a good level of gain, has superb front to back and offers excellent directivity in an antenna which is just a couple of metres in length. It has made a clear improvement to my band 2 listening. Remember also that, at the time of typing this review, conditions are well below average and I am suffering a lot of QRN when beaming east which is blocking weaker signals from Germany. I may need to consult OFCOM to resolve this.

A big thanks to Sven SM7DTT for the construction and Andy Webster for getting this on the roof. It arrived just in time for the Es too as today I received my first band 2 Es with Bulgaria, Romania and Hungary, received up to 93.5 MHz.

Good DX!

John