I thought about what you said and I plugged the tv aerial into the stereo (which recieves signal through a surface mounted antenna of course) and stations are all coming through very well.
Quick question, if I attach a splitter to the tv aerial, like this one :
https://www.toolstation.com/shop/p30919?table=no
and feed one into the stereo and another into the tv, would it work? Would there be a significant loss in the signal not to bother? What do you think?
The fact that you're getting some signal for FM from a TV aerial would suggest that you're in a fairly strong signal area. So, your question about the splitter, the answer is probably a Yes. You'll always lose some signal strength by splitting passively (a non-powered splitter) by it will preserve signal quality which is more important than outright power.
On a scale of 1 to 10 the reception from a TV aerial for FM radio probably ranks somewhere between 3 and 5. It very much depends on location i.e. whether it's a strong signal area, and how high the TV aerial is and whether it is blocked by other buildings/trees etc. If you're getting decent results with that, then a loft mounted FM dipole would give you something like an 8 on the same scale: Much more signal, less hiss, more of the distant stations.
The questions about your loft and current aerial layout were leading towards a suggestion of adding a loft mounted FM aerial and combining its signal with that from the TV aerial. This is the idea
Obviously for most DIYers this is only practical if the TV aerial cable comes in to the loft so that a splice can be made to fit a combiner. Hence all the questions. But if that is the case then the solution above will give you really good results.
The combiner could be a simple passive (non-powered) device, or it could be a simple loft amplifier with a UHF (TV aerial) and VHF (FM/DAB aerial) input. The output of either device is the combined signal from both aerials. This works because FM signals and TV signals work at different frequency ranges, so although they come down the same bit of coax they don't interfere with each other.
The signals are split back on to their separate forms by an outlet plate with sockets for TV and FM/DAB/Radio. The plate is a filter, so there's a bit of circuitry on the back but it doesn't need power.
Passive combiners are roughly £20. Active loft amps with FM and TV input combining start roughly £25. The outlet plates are somewhere in the region of £8.
By all means try the passive splitter you linked to in the previous post. It's cheap enough not to break the bank.
Digital TV reception works on a knife edge principle. It's called the Digital Cliff. Much like you standing on a cliff, you're safe enough right up to the edge, but one more step and you plummet off. Digital TV reception is the same. Signal power and quality can reduce and reduce but then there's a sudden point where it has walked off the edge of the cliff and TV reception just collapses. If the splitter adds too much signal loss then you'll lose the weaker channel groups first and shortly after the stronger groups.
