How was TV transmission made in east and west Germany so that viewers just a few blocks away, but in the other side of the wall, couldn't watch the same channels as the opposite side?

Firstly it is important to understand that the border between the Federal Republic of Germany (West Germany) and the German Democratic Republic (East Germany) was mostly a 'green' border, i.e. A highly protected line not unlike borders between other nations. What is known as 'the Wall' was localised to Berlin, the city which lay in the middle of the GDR was considered too important to go to one side after the war, so it was split between the Russians and the Allied Forces. The border between west Berlin and East Berlin was protected just like that between west Germany and East Germany as a whole ( but those lines did not touch) - however at first people are able to travel backwards and forwards within the city. Eventually the Wall was constructed in August of 1961. So for most parts of the GDR the distance to the Western border was actually quite considerable...this might help visualise this.

Nevertheless western television and radio channels could be (and were) viewed almost everywhere in the GDR. There were some areas where mainly topological issues prevented this. Both the West and the East wanted their programs to be heard/seen on the other side of the border so they placed strong masts close to the border, facing the other side to boost the signal. In the 60's the GDR did try to jam the signal but this was technically difficult without scrambling their own one. It was forbidden for civil servants, the military/ police etc to watch western channels (but there are studies showing that even they did watch it). However while it might not have been forbidden for the public to watch it, the general understanding was, that only the 'class enemy' would be interested in such media and therefore antennae pointing in the.'wrong' direction, knowledge of western programs/ music, children talking about these things at school etc would endanger you somewhat. Please remember that neighbours and even spouses were spying on each other. The Stasi documents contain ridiculously detailed information about conversations between people that were close...no-one could trust anyone. In such an environment you would make sure that only few people knew that you watched western channels.