All posts by Michael Perry
Below are all of Michael Perry's postings, with the most recent are at the bottom of the page.
Chris
Attenuators *do not* work with satellite systems! Fitting one in the downlead from the LNB will prevent it from working! The problems caused by excessive signal strength are confined to reception of Freeview from terrestrial transmitters. Satellite reception works completely differently. The whole system is designed to cope with signal variations and the main difference being the dish size, a larger dish collects more signal than a smaller one. In the UK it is rarely necessary to use more than a 60 cm dish in England and most of Wales but a 75 cm may be needed further north.
So I strong advise against try an attenuator in your coaxial downlead(s).
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D Hardy:
It is always a problem to bring the signals from 2 different aerials together without causing serious problems.
One possible method to consider is to use a shielded coaxial switch with 2 inputs and 1 output. The downlead from one aerial is fed to one input and the other downlead fed to the second input. You can the select which transmitter service you want to watch by manually 'flipping' the switch. I have successfully used that method to receive signals from Mendip and Oxford (they offer different 'local' news, etc). I have to stress that you should buy a good quality shielded switch designed specifically for UHF TV signal reception. The inputs and output may be either a 'standard' IEC coaxial socket or an 'F-connector' as is commonly used for satellite cables.
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Steve
Sky in more than one room is only possible if your Sky box has an RF output via a coaxial socket *and* your TV sets in other rooms have a UHF analogue tuner. The RF signal coming out of the Sky box, if it does have an RF Out socket, is in analogue format only with mono sound. You can carefully distribute that to one or more other TV sets that have analogue tuners but make sure you use good quality cable, good active splitter(s) and properly made coaxial plug connections. You can normally find out which analogue channel the RF output is set to from the Installation menu options on the Sky box.
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Briantist:
Not everyone uses Twitter nor other 'social chat' sites. Any use of these should always be in addition to normal postings here.
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jb38:
One other factor involved in how a picture appears to be is the transmitted bit rate. That differs significantly between Sky, FreeSat and Freeview. At my own location in North Wiltshire, Sky pictures are not as sharp as Freeview, I don't have FreeSat to compare with. In recent years broadcasters have been reducing the bit rate, and hence the amount of data transmitted, to allow more services to be included in a multiplex. You may have noticed that a PVR can now record more than it used to manage even with the same hard disk inside! That's due to the lowering of the bit rate and amount of data transmitted. Less data = less sharpness of the picture. They try to keep the data rate just about high enough to not cause excessive pixelation showing, but you will see some occasionally.
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John:
From my experience with installing and repairing satellite equipment I agree with Jamie. A zone 2 dish is larger so gathers more of the available signal to feed into the LNB. (Helps to make is less prone to snow outages in winter, etc.) Buy a good quad (at least) type of LNB with a very low noise figure to give the 'cleanest' signal. Then use proper good quality satellite cable with good F-connectors on the ends and wrapped in self-amalgamating tape to help prevent water getting in - but don't cover the end of the connector where the centre core protrudes.
Make sure you know where to 'aim' the dish - it is *not* aimed at 28 degrees east of south! You have to take account of the receiving location and the Earth's curvature. There are web sites that help get the Azimuth, Elevation and Skew angle for different locations. Do a goggle search for "satellite dish angles" and chose which option suits you best.
Good luck.
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D Hardy:
The problems referred to are what happens when signals from different sources but are on the same or adjacent channels are combined together. A combiner is capable to doing that well enough if the channels are well enough separated. If there are two transmitters using the same channel (co-channel) they can cancel each other out, meaning no signal from either source. If they are using channels next to each other, such as 21 and 22, then there can be cross interference between them with can give either no signal, intermittently no signal, no signal on one source (or the other, but unpredictable), etc.
The fact that this happens can give rise to confusion and result in constant re-tuning when that is usually not necessary and can lead to no signals and severe frustration.
Such is the way with physics.
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Samantha, Derby
If you have tried both radios next to each other and one works but the other doesn't then it is highly likely that the non-working radio is faulty and should be replaced. Can you borrow a similar radio from someone? If you can, place that beside your two radios in the same position and try them. If your suspect radio still doesn't work but your normal one and the borrowed one do then your suspect radio needs to be replaced.
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Mike:
There is no difference between a UHF aerial for analogue or digital signal reception! The only difference between the signals is the form of modulation used to carry the picture and sound information, but that does *not* affect the way UHF signals propogate through the atmosphere nor how they are received by the aerial. It os only the type of electronics design used in the TV set, or PVR, that changes.
Even the BBC state that there is no such thing as a 'digital' aerial and DigitalUK concur. So any good UHF aerial that it designed for reception of the channel group used by you local transmitter is all you need.
Generally, if you need an aerial that covers more than one channel group it is better to use a log-periodic design rather than a modified yagi often called a 'wide band' as they are poor at both ends of the spectrum and give lesser performance.
I have a PDF issued by the BBC Reception team about use of aerials for TV reception and it specifically states there is no difference between a 'standard' analogue TV aerial and a 'digital' one! I can provide that if you wisah to see it. Or search for "factsheet-tvaerials" at BBC's reception website.
I am a retired TV engineer and training manager having spent over 50 years dealing with radio and TV questions.
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Thursday 21 November 2013 10:39PM
GailC & JKF:
If you are not allowed to have a Freeview terrestrial aerial installed, your best option (in my opinion) would be to get a FreeSat box. That can use an existing dish that is aimed to get Sky services as FreeSat use the same satellites.
A Dish can *never* get Freeview as it is not a satellite based service but uses the same transmitters on the ground as originally used for terrestrial analogue television.