Amongst other things, I design, and my company installs aerial systems both domestic and commercial. (Caravan sites, etc - a site we have just done has 423 caravans running off one aerial)
To receive Freeview signals through your aerial you need a minimum signal of 45db (and not exceeding 75db) and a MER (Marginal Error Rate) over about 22ish. Unless you are right next to the transmitter, you are unlikely to achieve this with an indoor aerial.
If you are on a main transmitter you will get the full Freeview channel line up (about 85 channels) if its a relay transmitter you will only get 18 channels as relays only have three multiplexes. Wether the aerial is horizontally or vertically polarised depends on wether its a relay or main transmitter.
Depending on how far you are from the transmitter and the lie of the land, your old aerial may be ok, without putting a meter on it, its impossible to say what the exact signal its receiving will be. A decision is normally made after checking the signals as to wether a masthead amplifier is required and if so, what value. The aerial meters I have on each of my vans cost about £2500 + VAT each!
Its impossible to accurately say from here wether your existing aerial will give reliable reception as it is, however, as you are picking up some channels on an indoor aerial, I would guess that the signals are pretty good in your area, so you should have better luck with the outdoor aerial, its certainly going to be an improvement. Make sure you use proper connectors when joining cables and waterproof any joins that are outside with self amalgamating tape as if any water gets into the cable, it will end up in your tv. We sell 32 Element high gain aerials designed for digital for about £30 + VAT. Stuff that we use on blocks of flats etc can be 5 to 10 times that price.
50m cable run is pretty far in a domestic situation. Depending on the quality of the coax cable you buy, I would expect to see a loss of around 10db over the length of that cable run.
If you need an amplifier, then Vision stuff is the best.
Hope this helps...
If you need any more advice, let me know...
