Just to add my $.02 to this topic, there are advantages to high yagis and
low yagis- both quite different.
N2WK's M/M station at one time was set up with 7 el @ 70', and 6 el @ ~30'.
During June contests, the lower antennas was far superior on almost all Es
paths, including the double-hop stuff. The top antenna was far superior
for groundwave and auroral propagation (KFT doesn't have to worry much
about that one!). These were not stacked to do U/L/B, but might have been
worthwhile to try. My OWN station presently has a 7el yagi @ 28'. During
the summer, I've had tremendous success with it during the many single-hop
and multiple-hop Es sessions. I'm installing yet another tower, and the
setup planned is as follows:
80' - 7 el (28' Bm)
55' - 6el (26' Bm)
35' - 6el (26' Bm)
20' - 3el (6' Bm)
The top will be fully rotatable, and the 2 lower ultimately on side-mounts
(fixed for now, though) and phased with something like the WX0B Stackmatch.
The 3-element antenna will be pointed NE, tuned for 48.000MHz (used for
monitoring Eu videos) not part of the stack. I'll expect that, during
periods where F2 is the dominant mode - the highest antenna will rule. The
lowest antenna will be for Es - and quite frankly. I'm wondering whether or
not the middle yagi is really even necessary. That's an option - removing
that one from the equation. It'll likely help out the top yagi on
groundwave paths, and POSSIBLY help in Aurora, where I can scatter the
signal in 2-different directions.
I think the bigger advantage to locations are horizons. The reasons the
mountaintoppers do so bloody well is their extended horizons. If your
location is flat, without significant obstructions close-by - that's a
great VHF spot, too. If your towers are your HAAT, getting the top antenna
up as high as you can is really important - just like on 10m.
Remember - the modes of prop are the same (or similar) to 10m. Es, F2,
Aurora, Meteor Scatter, TEP, Groundwave, Backscatter. . .it's all there.
Duration is less in M/S - and frequency of F2 is far less. AND - quite
often you can't really know WHAT mode of prop is getting you to VK3-land
(True F2, F2-F2 coupling, Es-F2, Es-TEP. . .it varies by day). Having
multiple antennas to choose from DOES make all the difference.
Mark, K2AXX
Since our new reflector has been "broken in" by its first thread ("Software
Questions"), I'd like to start another.
K9TM and I are putting together some gear and antennas to have a permanent
VHF setup here at K8CC. In the past, the constraints of underground
feedlines (or rather, the lack thereof) lead to temporary summer lashups
that had to be ripped down once the HF contest season arrived in the fall.
One of the main questions to be answered here concerns the preferred
heights for the 50 MHz antennas. I've looked at the 50 MHz setups from the
K8GP and W2SZ web sites, but their mountaintop locations offer advantages
my QTH doesn't have. I found some interesting 50 MHz configurations at the
W5KFT web site, but Texas and Michigan are somewhat dissimilar in terms of
the available target audience.
I think I understand HF wave angles, antenna heights and stacking pretty
well, but my feeling is that VHF is a different thing. 50 MHz might share
*some* characteristics of 28 MHz, so some of those techniques might apply
if the propagation modes are known.
My location is essentially flat terrain, and I have towers that go up to
120'. My thinking is that really tall heights are not necessarily needed,
since anything above 80' (four wavelengths) is essentially free
space. I've been told that a 30' antenna can be a real killer at times for
summer E-skip, so I was thinking about identical yagis at 60' and 30' with
upper/lower/both switching for wave angle control and the ability to spray
RF in different directions.
Thanks for any suggestions.
73,
Dave/K8CC
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