All posts by Michael Perry
Below are all of Michael Perry's postings, with the most recent are at the bottom of the page.
To John Crabb
There is still a multiplex at Ch 48 on Mendip so if that is being received well then Ch49 should be as well. The problem you appear to have had is due to reflections within the cable that happened to resonate close to 698 MHz so shortening/lengthening the coaxial cable would change the resonance and possibly solve the problem. A well known phenomenon but us 'old' TV service men.
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To Dave Lindsay
No change to any other services at all on either receiver, testing software scans of stick output show 100% on all multiplexes. Only those on Ch 49 (ie BBCA multiplex) are affected.
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To Mazbar
That Ch48 is received very strongly means that Ch49 will be as well as long as it is a true C/D group aerial - it is of course as Mendip analogue transmissions were in the C/D band.By definition, Group C/D aerials cover 47 to 69 but if signal strength and quality are high then decoding should be fine - but it isn't on Ch49 and it IS on Ch 48! So aerial is not the problem. BTW, I'm a retired TV engineer.
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To John Crabb
An HDMI cable is carrying digital signals with fast rising edges, so can radiate and that may be picked up by a poor UHF coaxial cable. Always use good quality cables but don't waste money on the 'gold' plated ones - expensive does not mean good quality.
Any electronics book that covers RF signals up to 1000 MHz ought to have something about the relationship between wavelength, frequency and standing waves on cables of a length close to a multiple of the signal wavelength. A rough guide, 300MHz=1m and 100MHz=3m. So for a 600MHz signal avoid any multiple of 0.5m or thereabouts. Hope that helps?
A lot of waffle is spouted about aerials for 'digital' signals. The signal transmitted is an RF carrier so any aerial designed for reception of the frequency range can be considered. Aerial gain and reception angles are also important. A good C/D will suffice for Mendip now but a WB will be needed in a few years- the plan is to move Mendip into the Group A band around 2019!
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To Mazbar
Sorry I have been teaching engineering staff of a former major TV rental company covering not only the TV sets but aerial systems and satellite systems as well - since 1969! Before that I worked for Philips Electrical. So 59 years experience.
Don't assume that older aerials are deteriorating, it is the enclosed contacts that cause most problems if they are not properly enclosed and sealed. A good quality aerial, well fitted and properly sealed will last for many years. If Ch48 is excellent, it is, then 49 will be as well - it's only 8MHz higher up the band further into the central reception pattern of a C/D aerial.
A C/D group aerial will need replacing before 2019 anyway as they are changing bands for Mendip.
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To Mazbar
Signal reception of wanted channels is excelent strength and quality and I have checked the aerial system all the way to the aerial sockets myself (I do know how to do that). Huntshaw Cross has always been visible in the background but at a very much lower signal strength. That shares 3 channels with Mendip (Chs 48, 52 and 56) but not the signals on Ch49 where the affected services are located (Mux PSB1-BBCA), so not that either especially as one receiver is fine and the other not. Same aerial, active splitter, tried swapping to no effect.
Problem is strongly believed to be how the Hauppauge is responding to the moved channels.
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To KMJ, Derby
Good point, but not worth changing aerials too soon as the plan is not finalised yet, or so OfCom say. Mendip is a main transmitter for this area so if horizontal polarisation currently and has been since it was built. But the future changes planned will mean a change from C/D aerial and it may be that a WB will not be suitable either (it has reception in the 800MHz+ region where 4G will be).
It all seems badly thought through to me with so many 'retunes' being needed so often. Didn't have that anywhere near as much with analogue.
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Success! I have now solved the mystery of no BBCA channels on my Hauppauge WinTV stick. The software stores a database of your channel settings and that 'forces' it to think BBC is on a different Mux so doesn't decode them. I cleared the channel database (on this system that is in the Start>All Programs>Hauppauge WinTV>Advanmced Options> Clear Channel Database and then do a FULL retune. Now have BBC back.
I suspect that all who have lost BBC perhaps should follow the user manual and do a full reset (back to original factory settings) and then to a full retune (as they would have done on original installation), and then let us know how they get on.
Perhaps they could also let us know what make and model equipment they are using as I have a suspicion that some designs are affected as others are not.
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Are you getting the wrong BBC services? BBC1 West Country instead of BBC1 West?
Perhaps try restricting the channel search only to those relevant to Mendip (or your local transmitter). That should exclude Huntshaw Cross and others. Check your User Manual to see how to do that, but not all equipment has that facility I believe.
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Wednesday 3 April 2013 6:34PM
We are north east of Mendip, sitting on a hill above Calne, Wiltshire. All was well until Wednesday 27th March 2013. Now no BBC services at all but all others OK. BBCA multiplex has n=moved from Ch61 to Ch49 but that shouldn't make much difference after a retune. Humax retuned perfectly and all programmes available, but Hauppauge Nova-T stick in laptop has no BBC services at all. They don't know why.