[VHFcontesting] Suggestions on Antenna Heights for 50 MHz
George Fremin III - K5TR
geoiii at kkn.net
Fri Jul 27 06:19:51 EDT 2001
On Fri, Jul 27, 2001 at 01:09:57AM -0400, k8cc wrote:
> 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 dont think they are that much different.
The two most common modes of propagation for QSOs in a
VHF contest will be single hop (with some double hop - maybe)
E-skip and tropo / forward scatter range stations.
> 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.
As far as I can tell - 28 Mhz and 50 Mhz are VERY similar if you
remove the F2 propagation from your design goals. It is like doing
the 10m contest at the bottom of the solar cycle.
One diffrence I have noted is that the arrival angles seem to be much more
descret on 50 mhz then they are at 28 mhz. I have seen (very often)
when a station on an antenna at 30' was S9 and not copyable on
the antenna at 150' - then 2 minutes later working a station two grids
away from the previous one - I see just the oppisite.
Openings can be short - so it is good to have more antennas - at
diffrent heights and diffrent directions - so that you have less
chance at missing an opening because you do not have the
antenna pointed in that direction.
> 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.
I would suggest a low antenna - 30' or less.
And a high antenna - as high as you can get it. It is also useful if
this antenna has good to great gain and great pattern. This antenna
will be king when you are working tropo/iono forward scatter.
Beyond that - I would suggest some fixed antennas or arrays in
the directions where you get most of your QSOs.
So the W5KFT station (my design choices) is now usign this:
- Stack of 6 ele 34' boom yagis at 38' over 18' bottom fixed NE.
- 6 ele 24' boom yagi at 25' fixed towards Southern California.
- 7 ele 30' boom yagi at 155'.
- 5 ele 12' boom yagi at 25' fixed towards Austin (50 miles away).
We use a stackmatch so we can run ay of the first three antennas
or combination of these antennas.
I made a post in 1998 that I think covers some of this - I will
post it to the list - I am sorry I do not have time right now to
update that message or go into more detail.
George Fremin III
Johnson City, Texas "Experiment trumps theory."
K5TR (ex.WB5VZL) -- Dave Leeson W6NL
geoiii at kkn.net
More information about the VHFcontesting