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Tuesday 30 July 2013

OFCOM Visit & their evaluation of the Körner 9.2

Some good - and maybe also some slightly embarrassing news regarding my band 2 noise problems.

OFCOM visited me earlier today, their fourth visit no less! They couldn't have come at a better time too as my noise was pushing two bars on the XDR. That's - enough to add an irritating level of mush even to quite decent signals. However, it quickly became clear that the noise was not coming from the direction of the neighbours. It seemed to be coming from all around. After the conducted some DFing with a very nice little Rhode & Schwarz DFing loop antenna, the noise was traced to our own CCTV system. Bugger! On disconnecting this, all was quiet and there was very little noise across band 2 at all. It was almost 'DXpedition quiet', even when beaming towards the neighbouring property. I could hear lots of German stations via scatter right across the band, many at armchair levels!

Embarrassed? Well, let's say I felt a little awkward, but thankfully the OFCOM officials had seen the original problem for themselves during their first visit when I had disconnected the entire power supply to the property and they could clearly see the noise levels which were radiating from the direction of our neighbours. There's no concrete evidence that the noise is coming from our neighbour's property, but it's certainly from that direction.

What I hadn't realised until today was that our CCTV system had become noisier than it was a few weeks ago and it was this which had been causing the recent increase in noise levels. The 'neighbourly' noise must have been buried underneath the CCTV noise. Today though, things were quieter than I have heard them in more than a year.

With the CCTV drive switched off I can still detect a little noise, but it is far less severe. I don't expect it to last of course, considering the nature of modern equipment and PSUs, but at least the band is beautifully quiet at the moment.

Körner 9.2
While OFCOM were here, one of them asked about the gain figures on my Körner 9.2 antenna. From memory I said something like 8dB or more. They thought that was too high. Unknown to me at the time, one of them connected the 9.2 to an expensive looking analyser test gear thing and was checking the performance. He responded with a "wow" and showed me the response curve across band 2, showing it to be at least 8dB across the entire band, peaking around 8.5dB at 88.2 MHz. I cannot remember the detail but I think he referred to 'dBd'. We had a discussion about the antenna after this and my poor brain cell became confused and fell over so I hope the facts here are correct.

What is clear is that this 9.2 antenna is an absolute beauty and I cannot praise its performance highly enough. This is impressive when you consider that the 9.2 is only a couple of inches longer than the Triax FM5. Full credit to the designers.

Cheers

John

2 comments:

  1. I assume the antenna was beaming at a reference signal then turning the antenna and checking the full band whilst doing it . I agree the 9.2 is a good antenna but think what the larger models can do .

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  2. Hello Anonymous.

    I don't know exactly how the OFCOM guys did their evaluation. I am sure they will know what they are doing. Their figures agree with the spec given by the manufacturers anyway. Oh, and it was dBi apparently, not dBd as I mentioned above.

    Yes, I am quite sure larger antennas would be still more impressive. Unfortunately, most of us have our space and planning limitations.

    One thing which is worth remembering though, the laws of diminishing returns come into play, so if you want to improve on a 9 element, let's say, you would probably need a 15 or 19 element, and so on. But the returns are such that there seems to be very little difference in the performance of the 9 element and the 15 element Körner. I am sure any improvements would be noticeable, but by how much? 2dB tin gain typically? That would be less than half an S point in practice. The extra directivity would undoubtedly be the main benefit. Personally, I know that would be too tight for my own preference having missed some openings this summer on the 9.2, thanks to its superb directivity. It would be interesting to see a detailed comparison though.

    A 15 element would be out of the question here but I am more than happy with the performance of the 9.2. If I had the space though ... :O)

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