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
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 .
ReplyDeleteHello Anonymous.
ReplyDeleteI 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)