Aerial recommendations - rural area

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Hi All,

Our aerial has died. Not sure what's wrong, but I plugged the telly into a neighbour's aerial the other evening and it found plenty of stations, so I'm assuming it's the aerial. It is currently on the chimney stack. We're about 10 miles from our local mast (Caldbeck in Cumbria), and there are hills involved. We're right on the edge of its "good" reception area on the map, but used to be able to get most of the Freeview stations OK. We have a signal amplifier in the line at present.

I was wondering about a loft aerial this time? Would I be wasting my time? Current aeria lis about 15 years old.

Also I've seen these new "Digidome" ones advertised. Are they any good?

https://www.amazon.co.uk/dp/B00D76G...=9045237&hvtargid=pla-441259973446&th=1&psc=1
 
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Might be you need new coax cable.
Its not expensive to have someone round to fit new antenna & renew cable.
Probably last another 15 years.
 
Digidome said:
Unique technology receives all locally available digital TV signals, suitable for most signal strength areas and frequency UHF 470 to 790MHz

That does sound good but if you are in an area where two different transmitter sites can be received then a directional aerial might be necessary to ensure signals from the un-wanted transmitter do not affect the signals from the wanted transmitter.
 
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Short version: Hell, no. Omni aerials are rubbish for TV, and lofts are terrible places if you already know that the local signal strength is poor.


Longer version:

You should only consider a loft aerial if you're in an area with a very strong signal. It doesn't sound like you are.

Putting an aerial in a loft can easily knock off 10dB of signal level. 10dB is a huge amount to lose. That's close to the equivalent of putting the signal through a passive splitter which would halve the signal, then doing the same again (so now 1/4 the original amount), and then doing the same another time. You end up with 1/8th of the original signal level compared to mounting the same aerial on the chimney stack.

Add to this loss another amount because the aerial is lower by a couple of metres.

Handicapping the reception capability of your aerial system in this way is bad news. An amplifier can't get back what isn't there. Nearly all the time an amplifier is talked about, the only thing discussed in the reseller's blurb is the signal strength. They never discuss signal quality. That's a big problem.

If you haven't come across discussions about signal Quality before, then what it is is the difference between the signal and the background noise. We refer to it as Signal to Noise Ratio (SNR). The bigger the gap between signal and noise then the better the quality of the signal and the more it can stand up to cable losses or being split or amplified. There's only one place in any aerial system when the SNR can be influenced; this is at the aerial.

Poor aerials, or aerials in bad positions, will generate very little signal level compared to the background noise they also receive. This combination of the transmission reception plus background noise then becomes "the signal". Buying a better aerial, or putting a good aerial in a better position, increases the SNR because the aerial picks up more of the distant transmitter signal compared to the local background noise.

Using an amplifier to boost "the signal" amplifies both the transmission reception and the background noise by the same amount. However, the amplifier also adds its own noise to the signal, so this makes the SNR worse, not better. All any amplifier can do is amplify what's coming from the bits of metal pointing directly at the transmitter plus any background noise they also pick up. If the signal is crap coming from the aerial then any amplifier - regardless of where it's situated, even on the aerial itself - then all you'll end up with is 'loud' crap.

Now if we bring this back to a TV tuner; they discriminate on SNR and not on signal power. A 'quiet' signal with good SNR will give better results than a 'loud' signal with a lousy SNR.


Next, let's have a think about aerial shapes. Most outdoor TV aerials look like a long bar with some metal fins. If you look at the houses around you, you'll find that most aerials point in the same general direction. The design is no accident, nor is the alignment. The fins are the bits picking up most of the signal. The best signal is generally when the fins are perpendicular to the signal waves from the transmitter. This is when the long bar is pointing straight at the transmitter. The greater the number of fins (they're called directors) then the stronger the signal compared to the background noise.

You might notice that some aerials point in slightly different directions. That's because signals have a habit of bouncing off solid surfaces such as buildings. This was more of a problem with analogue than digital, but you've no idea unless the aerial looks new just how long it has been up or whether the installer knew what they were doing.

Now ask yourself how many round TV aerials you've seen.

That's what this Digidome aerial is. It's a halo of metal inside a fancy plastic case. If round aerials were the best idea for TV reception then the roofs of houses all around you would be festooned with them. So why aren't they?

1) Lousy SNR: A round aerial presents only a very small amount of metal perpendicular to the signal source, so the amount of transmission signal received is very low compared to the background noise that the aerial picks up.

2) Our TV reception comes from just one direction, not all round: Unlike radio, where we receive signals from lots of different transmitters, TV reception is designed to work best where the aerial points at the local transmitter, and where it does its best to ignore the slightly weaker transmissions from other TV masts.

3) Lots of amplification doesn't make up for a lousy signal.




There are a few reasons why you might have lost signal with your current aerial. Issues with the coax cable have been mentioned already. The aerial could have moved on its bracket. Perhaps the ongoing retunes have moved the transmissions to frequencies where your aerial isn't that efficient. There could be an issue with the current amplifier or its power supply. Maybe it's a combination of faults.

Whatever it is, living in a marginal transmission strength area and putting up a low signal quality aerial in to a signal lowering space such as a loft really isn't the way forward.

Although there isn't such a thing as a universal aerial, a good choice for most applications is a Log Periodic. These are a low gain aerial, but they work efficiently across the widest band of frequencies which makes them suitable where transmission frequencies are spread over a wider range than a narrow-band group aerial can cope with. Put one of these in place of your current aerial, and have it wired up with Webro WF100 - an all-copper coax cable - or the equivalent from Triax (TX100) or Labgear PF100. Cable to avoid is anything sold as RG6 or nondescript "low loss TV/Satellite cable".

RG6 isn't a cable spec, it's simply a description of physical size and an impedance of 75 Ohms. It's about as descriptive for cable specs as 'Size 11, black' is for footwear. You could be talking about Brogues, clogs, hobnail boots, Wellingtons, slippers, ski boots or divers fins. WF100/TX100/PF100 are all RG6 cables, but their performance and longevity is a country mile away from the rubbish typically sold as RG6.

The problem with what's typically become know generically as RG6 is mostly with its longevity. The stuff breaks down under UV from sunlight quicker than the quality cables, and when it does, and water gets inside the outer sheath, then it reacts with the aluminium braid which then corrodes quite quickly. If you're putting power up the cable to a mast amp or amplified aerial such as that Digidome, then the cable can die within a year. The home owner is then faced with the task of paying for the cable to be replaced. Buying cheap coax is a false economy.

If this or any other reply was helpful to you, on each one please press the THANKS button which appears when you hover the mouse pointer near the Quote Multi-quote buttons.
 
Thanks All - and particularly Lucid, for the entire textbook! I'm very grateful for the trouble you've gone to!

The aerial is still there and doesn't look like it has moved. The co-ax from it trailed along the roof for a bit, before going in between a couple of slated and into the loft. My guess is that it has snapped / corroded, or in some other way failed. I don't get poor reception, I get absolutely zero on any channel.
 

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