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All posts by Nigel Johnson

Below are all of Nigel Johnson's postings, with the most recent are at the bottom of the page.

Channel 27, which carries the BBC mux, on Sandy Heath is still unusable most of the time. All other Sandy Heath channels are received without a problem.
This is strange as the channels paid for by the TV licence are the only ones we cannot receive. I think it is time that BBC mux is switched to a better aerial on the Sandy Heath transmitter.

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I think I have solved my interference problem. Today I had fitted an A0968 28 element log periodic aerial, this replaced the 52 element HG10 WF aerial that was fitted. The improvement in reception is considerable. Although the gain of the new aerial is 4dB lower than the old one, the reception is greatly improved with no bit errors detected on any channel. I have to say the new aerial is mounted on a longer pole, putting the aerial 6ft higher above the roof top. But that said, it may now be necessary to turn down the gain of the distribution amp mux, as all Sandy Heath channel are at the top of the equipment signal strength range, close to overload on one of the DVRs.

Interestingly the new log periodic is smaller than the old aerial, and clearly offers a much lower wind loading.

What I do no understand is why the old aerial produced such poor reception only on one RF channel, channel 27.

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The argument that gain was the issue is clearly incorrect as my new aerial has a slightly lower gain than the old one and experiments were conducted using an aerial preamp that indicating front end gain was not a factor.

As I reported in my earlier postings, my receivers were all reporting high levels of signal, the problem was poor bit error rate.

The way in which the bit error rate changed with time of day suggested that the interferer was a strong reflection subject to Rayleigh or Rician fading.

Since the new aerial made such a difference, I can only conclude that either the old aerial had a notch in its frequency response due to an impedance mismatch problem, maybe the result of a poorly connected cable, which seems unlikely or the small increase in height and the slight change in aerial direction, was sufficient to mask the co-channel interferer. I will not know if the problem has been truly solved until we have experienced the full range of weather conditions.

Given the beam width of the old aerial is 32 degrees, the slight change in direction also seems unlikely to have resolved the problem.

It is worth note that the minimum front to back ratio of the new aerial is better than the old one, with large attenuation peaks across the band. A more complete comparison of the aerial specifications is impossible as the old aerial spec lacks the necessary gain plots.

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If is any consolation to those who will lose their TV signal, the companies that intend to run 4G are likely to be running at a considerable loss for a considerable period of time.
The business case for 4G is so weak and the advantages to the users so restricted we may see the companies happy to hand back the license. After all, if 4G users do not want to watch TV on a mobile, a 4G phone has little to offer.

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Sandy Heath (Central Bedfordshire, England) Full Freeview trans
Saturday 28 September 2013 10:27PM

During the summer months I was able to receive all the free view channels without any problems.
Since the latest engineering work on Sandyheath, my television reception has been terrible. The signal strength remains very high at all times, but the signal quality is zero a lot of the time. The BBC mux is most affected, but the interference moves across the band.This sound like massive multi-path interference .What have they done to the Tx aerials or are they playing with the linarity of the PAs?

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I am a little surprised that the interference is co-channel, as it moves up and down the whole band. Given the structure of the frequency plan, I would have expected co-channel signals to be limited to a few mux frequencies, That is why I suspected it was multipathing from Sandy Heath. I suppose it depends on the channel equalisation specification of the receiver.

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There now some indications that the days of RF transmission of television are numbered, at least for dedicated TV transmitting stations. The future appears to be television over the internet. The BBC is releasing some content here before transmission over the air. We can expect some content to be only available via iTunes. Internet broadcast is also a requirement if picture quality is to be significantly increased above that of HD, with download and play later being the standard. This is due to bandwidth limitations of RF transmission. No doubt the new model will no longer require a TV license, but will need a very expensive subscription. I would not be surprised if that is the reason there is little government concern about the signal quality of digital TV transmissions or the impact of 4G interference. It all helps to push users to cable and internet based services, where the real money will be made.

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Should have written iPlayer and not iTunes, but I am sure you get the picture or rather you won't soon:-)

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Do not assume the technology covered in my last post is for the benefit of the consumer, it is all about extracting the maximum amount of money from the viewer. As I have pointed out before, 4G is an expensive, and pointless, one trick pony. The only virtue of high speed data download is to allow HD video to be viewed while mobile, it is not going to improve voice communication, in fact it may make it worse, as the system requires a higher density of base stations cells to operate. Ok for the city, not much good for the rural user who just want to make a voice call.
Similarly, I suspect the 4K plus TV services will be used as a conduit for the sale of premium rate, DRM protected, movie and sports content. This is evident by the added DRM protection included in the revamped BBC iPlayer.
By forcing users to view online content, advertisers will know exactly who is watching what and target their ads accordingly. This is a direct result of having more channels on digital TV, as this has reduced the size of the audience for each channel, thus reducing the cost effectiveness of mass broadcast advertising. So how is this relevant to FreeView? Well clearly its days are numbered, with vested interests keen to move consumers to internet TV and make them willing to pay for the infrastructure costs of doing so, at the same time freeing RF spectrum for yet more mobile comms and eliminating expensive TV transmitters.
So do not be surprised if the quality of FreeView services are not considered important. I may be a little paranoid, but poor quality may well be part of a bigger plan. I believe the government has yet to realise the downside, which is the loss of a fast, universally, communication medium with the viewing public.

By the way my ADSL download speed peaks at 12Mbs, no where near the 30Mbs, minimum required for this brave new world.

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Wish these posts had an edit feature, I never seem to get my posts right in one take, missed the word watched after universally.

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