I have been thinking of building a base station 2m and 70cm antenna. I like 
the diamond x-200a or x-300a designs but would like to try building one 
myself. the antennas are rated at 6 to 6.5 dB on 2m and 8 to 9.5 dB on 70cm. 
But does anybody have dimensions of this type of antenna? I found several 
J-pole designs but no 5/8 wave collinear designs with radials similar to the 
Diamond x-200A or x-300A antennas.
Anybody have any thoughts?

Would a 8 foot center element (two 5/8 waves in series simply work? would it 
match to 50 ohm coax? will it match on 70cm?

thanks
73 Neil k8it