Here's another version of the late W3IY's experience in stacking VHF
antennas for different bands:
Many rumors and misconceptions exist in the amateur radio world about
stacking VHF/UHF antennas on the same mast. I have heard all sorts of
warnings about screwing up the performance of my yagis by mounting them in
a compact fashion on my rover masts. I have been modeling antennas using
NEC2, and I am here to tell you that you can really get away with a lot,
and still maintain good antenna performance. For example, I am considering
adding a medium-sized 2m beam (12-15ft length) on my rear mast, just below
the 432 yagi. I wanted to know how close together these yagis could get
before the 432 gain went to hell. Well, I found that I could safely stack
them, at a distance of only 2ft, and only lose about 0.5dB of forward
gain!! ...and the pattern is still very good! This is a pleasant
surprise. I always suspected this, from previous experiments, but I wanted
some computer modeling to really convince me it was OK...well...guess
what...IT IS...JUST DO IT! I have always been pleasantly surprised, when I
have stacked yagis close together. You don't need to worry about that old
ARRL VHF handbook recommendation of "half-the-boom-length" of the upper
yagi. Ed Tilton was a great guy, but he was also pretty conservative about
antenna stacking (and he didn't have computer modeling like we have today).
If you look at my QRZ page, you will see that I have done just what
Bill's experience has determined, i.e., JUST DO IT! On Tuesday's 222
night, with 100w and the 16 element Yagi, I work Dave, K1WHS every week at
500 miles out. Plus N1GC and K9MRI around 300 miles. So close spacing
must be working ok. WA3EOQ
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