Mike in Texas emailed me recently to ask about the construction of the antenna mount that I use with the Yaesu G-5500 rotator. The mount allows for two 2m yagis to be used on the same az/el rotator as a 70cm yagi. Here's an overall photo of the current antenna array:
And here are the construction details of the "bridge" mount:
The advantage of the bridge mount is that it lets me use the same array for V/U satellites, U/V sats, and 144 MHz EME. The antennas (a M2 440-18 and two M2 2M7's) have more than enough gain for the current fleet of amateur satellites -- typically only 2.5 watts is necessary to work the sats.
I use a metallic crossboom so that I can use vertical polarization on the VHF antennas, and run the feedline along the crossboom without adverse interactions. To keep the antennas low-profile (tucked in behind the roof corner of the house) I need to keep the feedlines from hanging off the rear of the array, therefore vertical polarization is suitable.
So far I haven't been able to detect any adverse interaction between the 70cm yagi and the two 2m yagis for EME operations. The 70cm yagi is horizontally polarized, and placed roughly mid-way between the two 2m yagis which are installed as per manufacturer's specs for stacking. With the two 7-element 2 meter yagis, I've been able to make around 130 EME QSO's with 100 unique stations in 25 countries over six months of operating.