Aerial woes

haxxbaxx · 23 Mar 2014 at 10:52

I recently got a talktalk youview box but I'm having so many problems with it receiving signal. Without it I get every channel with a bit of interference every now and then but when I try on the youview box it struggled to find around half of them.

My question is; can any recommend a new aerial (if it is a aerial related problem)?

lucid · 23 Mar 2014 at 15:44

If you plan to change the aerial then go for a Log Periodic with an adjustable mast head amplifier.

So called wideband high-gain aerials only really work at peak efficiency over a very narrow frequency range (see graph). That used to be okay for many locations where the channel transmissions matched the aerial's gain characteristics; for example the North West. But since the switch to Digital, and the addition of new Freeview and Freeview HD broadcasts, and the Government selling off channels 61-68 for 4G then these aerials are no longer the best choice. The channel bands are being pushed lower down the frequency range to where a wideband high gain doesn't doesn't work that well.

The two alternatives are Log Periodics and Grouped aerials.

This last category are more peaky than wideband high gains but at least better match the channels from certain transmitters. If the channel arrangements were staying "as is" then they might be a reasonable alternative. But that seems very unlikely in the medium to long term. Governments see the airwaves as a cash cow. Grouped aerials are no good if the channels required are at either ends of the frequency range, as is the situation in the North West. The regular Freeview channels from that transmitter are now from Ch 49 to 59 post 4G. But if you want the extra Freeview HD channels then you also need to pick up channels 31 and 37. A Grouped aerial is no good for this. A Log Periodic is the sensible choice.

haxxbaxx · 23 Mar 2014 at 15:51

Thanks for the detailed info, funny you should mention the north west as I live near southport

any recommendations of a particular aerial ?

lucid · 23 Mar 2014 at 21:36

Any of the full sized Logs should do for you. But is this going on the roof or in a loft... or elsewhere?

haxxbaxx · 23 Mar 2014 at 22:34

Well I would probably go for a loft one as I don't fancy climbing around the roof, however would that impact performance? Surely a roof mounted one would be better, or is there negligible difference

lucid · 24 Mar 2014 at 17:25

We reckon on about a 6 to 10dB loss of signal just for being in the roof, but the losses can go higher depending on position in the loft, obstructions and the channels being attenuated. The losses increase too when the roof is wet because water is good at stopping signals. a lot more. To put the numbers in perspective, 6dB is a halving of the signal power level.

You and I live about the same distance from the Winter Hill transmitter, although in different directions. Winter Hill is my local transmitter too.

I have a Log Periodic on my roof. I use it as my reference aerial for comparing the performance of other aerials. It's unamplified and the line of sight to the transmitter is excellent. There are no trees or buildings or hills in the way. I get all the Muxes except for the very low power MEN Mux which is broadcasting to central Manchester.

The signal difference across all the received Muxes is +/- 2dB. That's really very very good. It means that there's none that are too strong or too weak relative to each other. The signal strength at my TV is an average of about 61dB, and again that's another very good result. I can afford to lose 12-16dB quite easily and still get perfect reception. In other words I could use a passive splitter and take two or three extra feeds off this signal without any issue.

The thing with loft installs is it's very much suck and see. You've got pretty strong signal in the general area. If the house has good line of sight to the transmitter then that definitely helps. The flip side could be you're on the wrong side of a pair of semis so your aerial is looking through the dividing wall and next doors roof too. Worst case you live in a mid terrace and your aerial is point through half the roofs in you street

Then there's the position in the loft itself. Go for the middle and equidistant from the opposing surfaces and you'll be in with a shout of reasonable results. Too close to the wrong side of a gable wall or water tank or the roof tiles themselves and you could knock off a further 6dB of signal. You have to experiment.

A Log Periodic like mine, combined with a 0-10dB variable (adjustable) mast head amp should see you right. I'd always go with a remote power amp rather than something powered from a socket in the loft. It's safer that way. If you want I can put together a package of aerial + amp + connecting cables & plugs. I can let you borrow a decent semi-pro meter too so you can get the aerial location nailed.