Weak signal on transponders

[babycakes]

I am in ex c&W Harrow and have a DM500 box. Why is it that the maj0ority of transponders have a reasonable signal but some like 77 and 7F are really weak and affect E4, Sly Sp0rts1&3 etc.

If I introduce an amp, then it boosts the weak transponders but overloads the good ones.

Anyone able to help?

[nbtechnic]

nowadays the problem no longer arises, we buy a transponder programmer and we solve the problem!