Hi Tesla!
I've built the pyramidal horn with two sides as you described. I used a coax balun with 4:1 ratio, but the signal reception though much much better than before is a bit weak (dots on the video, audio very clear).
So, first of all
Hats off to You, Thanks!
Secondly, to improve on this, must the antenna be at a certain height above ground?
Thanks once more.
That's great - it does give great results for little effort.
Now for some of the other details of radio reception (you are progressively opening a can of worms..)
How to improve your signal further:
1. Height - very important. If the land around you is flattish then each time you double the height of the antenna you get 6dB more signal. (If you are on top of a hill then the local height matters less.) So long term there may be a case for making a ruggedised external antenna and mounting it at the top of a pole. Be careful that you don't lose the extra signal you get in cable losses. If your cable loss is significant (look up cable specs) then you can use a masthead amplifier.
2. Preamplifier - most TV sets don't have a good noise figure. You can generally get better performance by using a low noise amplifier at the output of the antenna. Be careful though if there are any strong signals around within the bandwidth of the antenna / amplifier as you may overload the amplifier or TV and degrade performance (filtering may be the answer in these cases).
3. local obstructions - try to make sure that your antenna has as unobstructed view toward the transmitter as possible, if indoors try to point out of a window instead of through a brick wall, close by trees etc.
4. Polarisation - just checking that you understand the polarisation of the horn and your signal, if not, try rotating the horn through 90 deg (still pointing at the tx) and see what happens.
5. Gain - if it happens that you can fit in a bigger horn then go for it.
At this stage, once you have found the best place for your horn, playing with a preamp may be the best bang for buck. I have used a MiniCircuits monolithic amplifier (something like an ERA-3) at times, these are pretty easy for you to play with, you can experiment with the RFC (wind your own is OK) and all you need are two blocking capacitors. I don't know what is available locally for you. You can make discrete transistor ones, there are circuits around, probably a bit lower noise but also more complex.
Enjoy the TV!