I have had a backup aerial in my loft for many years due to occasional problems with the roof aerial. Currently it is a small log periodic which actually works surprisingly well although reception on some independent channels can be a bit hit and miss at times.
Anyway, I want to change this for something with better performance but which will still fit in my quite small loft. Realistically, the maximum length would be 1200mm, width about 300mm and a fairly compact reflector if it has one. Luckily, I can cradle mount it if required as my loft has cross beams at waist height.
I am in south Cumbria and use the Winter Hill transmitter which works well for my loft orientation. I have looked at a few aerials but don't know where to place most importance, ie. transmitter group, gain, directionality, front to back gain etc etc. Any advice would be welcome. This aerial will never be used outside so resistance to the elements is not an issue. Thankyou.
Your current aerial is a small Log Periodic, you said. Logs are always wideband, but how big that band is has changed over time. Originally it went from channel 21 up to channel 68. (Each channel number is a progressively higher frequency in megahertz.) The aerials have coloured markers on their ends. A ch21-68 wideband would have a black marker.
When they sold off the 800MHz range then the new TV range went from 21-60. This is known as a T Group wideband. The end marker would be black also. Then they sold off the 700MHz range, so we now have aerials going from ch21~49. These are K Group widebands. The coloured marker is white or grey.
The reason for telling you this is so you can gauge how well your aerial is doing at pulling in signal.
First, it's in a loft, so the signal has to penetrate the roof tiles and maybe even pass through an adjacent loft. When the tiles get wet they block more signal too. Second, if this is a small Log Periodic - about 12~15" / 30~40cm long rather than the 36"~54" / 1~1.3 m for a normal-sized Log - then it's going to pull in less signal. Finally, if it's covering the full 21~68 range then what signal it does pull in will be spread over a much bigger range than one of the narrower band Logs.
What all this means is that you could go for a new Log Periodic - full size - and be pretty confident you'll get more signal. Have a look at the DM Log from Aerials & TV
LINK This will hit the mark for your size limits. Scroll down the page to the graphs. There's one that compares the DM Log against a mini Log. The DM Log gives you more gain right the way through the range.
If you want more gain than this then you're going to move away from wideband aerials into the narrower frequency range of the Group A aerials. It's Group A because its reception is concentrated on the bottom half of the new 21~49 frequency range. That matches the transmissions from Winter Hill now all the channel shuffling is over.
Since the aerial is focused on a much smaller frequency range, all the reception power is concentrated. This means that the aerial should have higher gain.
From the ATV site again, they have a graph for one particular aerial, but versions of it for the various band coverage ranges.
The black line is the old ch21-68 wideband. The grey line is for the smaller range of the K group aerials. You should be able to see that the grey line sits higher than the black from ch21 through to the now defunct ch53. That means more signal. In this case, about 1.5dB more.
The red line if for a Group A version of this 18-element Yagi. The 'hump' in the gain curve is a bit more pronounced. Compared to the Group K aerial, the gain advantage rises from about 0.5db through to around 3dB extra. Do bear in mind that the gain curves and predictions are for the aerials that ATV sells. They've tested ones from various manufacturers. Some were good, others mediocre or poor. The point here is that if you buy from say Screwfix or some online retailer, it's very likely that the aerials won't perform to the same standard.
For loft installations, ATV recommends its
XB10A. This crossbeam (XB) aerial has a lot more gain than the DM Log, however, the reflector is going too be wide for you. It's almost 60cm wide.
