You just can't take two 50 ohm antennas and connect them together. First of all, you need to space them apart to allow them to work together. This is nomally a little over a 1/4 wave.
Next, you just can't take and tie two 50 ohm coax cables together at a tee. This would not be a 50 ohm connection point. The combined termination point at the tee would be someplace much lower than the desired 50 ohms. The solution to both these problems is to make a section of cable be a transition for the impeadence back to 50 ohms.
Normally the transition is done with a section of 75 ohm coax cable. Some of the antenna manufacturers even have some coax cable that is around 35 ohms.
There are other cable types that are used to make this transition. DB has some interesting cable they use on their antennas. If you look at the harnes on one of their antennas, you will see several cable type numbers used. All of them start with "VB" for vapor block. This prevents water migration in the cable. Anyway, you will see numbers like VB83, VB8, VB35 and the likes.
The lengths will vary, but you should find them to be in some sort of 1/4 wave length or multiples of it. The lowband dipole arrays need more cable length between the dipole elements. Yup, they do make a 4 dipole array. Makes a fine antenna for 6 meters. Only problem is it is rather expensive. Only problem it takes a great deal of verticle realestate on a tower. Some place around 60 feet if my memory is still with me.
Hope this comes close to answering your question.
Jim
