These calculators reveal the exact dimensions to avoid aperture overlapping and deliver optimum performance!
If you want to stack Yagis there are two choices for feeding them. You can use a 'Power Splitter' or 'Phasing Harness, the latter in my view being a simple and cheap option.
Your feed system is based on 50 ohms impedance. However, the harness arms will need to be constructed from 75 ohms cable, UR57 is one possibility. Run the main feeder length, taking it to a central location on the 'Stacking Frame' (support structure). Here you will need to make a 'T' joint from which the 75 ohms
arms radiate. Each of the arms will need to have sufficient cable length to reach the Driven Elements via the frame and booms. Include an odd ONE-quarter wavelength ie; 3/4, 5/4 or 7/4 total length etc. This is MOST IMPORTANT! RadCom has given details in the past of making such joints. Keep lead lengths as short as possible and cover the joint with layers of
Plumbers PTFE, Self-Amalgamating AND PVC tape (alternative use Denso tape). The latter prevents UV damage. Solder connections carefully! Use a spacer to keep inner and outer conductors apart (I suggest pieces of polythene dielectric material that cover inner conductor [maintain spacing distance to preserve impedance]).
The 'Velocity Factor' (Vf) of the cable reduces its physical length. This is taken in to consideration in MY calculator below. For two Yagis there is ONE 'T' joint and for four Yagis THREE. And TWO arms for two Yagis and SIX for four Yagis.
Confused? read carefully what I have said, sketch out your feeder layout. The RSGB and ARRL VHF/UHF handbooks may help! Finally, make sure the Driven Element polarity's are all the same.
