This isn't my local area, but online sources suggest that Waltham currently uses RF channels between 29 and 55. However, RF ch55 is temporary. Once the final reshuffle and channel moves are done then it will disappear. It looks like the range will be RF ch29-48 after that.
There's a signal level predictor site called Wolfbane. It's possibly a little out of date now, but if you take the results with a pinch of salt then the suggestion is that Waltham to Crowland gives something like a 45dB field strength. What that says to me as an installer is that I should be prepared for a fairly weak signal in the general area. The caveat here though is that Wolfbane can't predict the results for a specific address. Local conditions have too big an effect. A house with a bit of extra elevation, or somewhere flat with no line-of-sight obstructions could help. The flip side could be a loft mounting with the aerial effectively point through some other buildings too which would reduce the signal even further.
45dB is what I'd consider to be the lowest threshold of signal at the TV aerial socket after any loses from cables and connections have been factored in. Ideally though I'd be looking for something in the 50-55dB range.
For a roof mounted aerial on the end of say 15m of cable, then the system losses would amount to around 3-4dB, so I'm looking for the aerial to generate between 53 and 59 dB to get 50-55dB at the TV end. With a loft installation then I know I'm see a further reduction in signal level by about 3dB in the dry and anything up to 6dB when the roof is wet.
Pulling this all together, you're either going to have to get an exceptionally high-gain aerial to make up the signal level shortfall, or be prepared to add some amplification. When the aerial moves from indoor to outdoor then you may find that it's not needed, or at least not as much, and so some kind of amp with an adjustable level control for gain would be a sensible move. This does all hinge though on whether real life follows the model prediction. I can tell you right now, it doesn't always work that way.
If I was to take Wolfbanes prediction for where I live then I'd be in a similar boat to you. But I'm not. I have tonnes of signal. There's enough that I could split and feed 3 TVs with a simple passive splitter and still hit 100% Quality and 80% Strength on all the main muxes.
So, what does this mean for you?
I think your best plan would be to do this in two stages. The first part is putting in the aerial to see whether the predictions are correct. On the aerial choice, the highest gain aerials are massive. You're looking at anything from 6ft to 7.5ft long!
See this Crossbeam XB16K. That's fine outside, but not very practical in a loft. However, if the local field strength is higher than predicted then you could get away with a shorter aerial more suitable for lofts without giving away too much gain. A
Crossbeam XB10K would be a good start. That would still be really good outdoors too. The second part is seeing if you then need some additional amplification after the loft installation is done.
There are other aerial options. A
Log36 is perhaps one of the most compact and it offers more gain than the standard Log aerials sold by the DIY sheds and catalogue suppliers such as B&Q, Argos,
Screwfix and Toolstation. None of these places are aerial specialists, and so their stock is chosen on the basis of what makes the most profit for the retailer rather than what's the best choice for the purchaser.
All the links posted point to
AerialsandTV. They're a really knowledgeable reseller with a stock selection that you won't find in the DIY stores. For the record, I have no affiliation with the company or its staff.
