On 12/27/2011 6:55 PM, john@kk9a.com wrote:
> A vertical is not a great antenna on 40m, unless of course you have the base
> in salt water. I just did a quick model of my lower shortened 2el 40m beam
> which is at 75 feet and a vertical that I had already had a model of (which
> was not elevated). The low yagi is 11dB stronger in the direction that it
> is pointed at most useful lower radiation angles. The yagi is even 4 dB
> stronger off the back. I did not compare the side lobes, but a 2 el beam is
> not that directive so I doubt that the single vertical would ever be better
> except for very high angle radiation which I have never seen on 40m. I do
> not think that you can contribute your poor vertical performance to tree
> absorption.
I do agree about the trees unless the tree(s) are really close to the
vertical.
This is only one operator from two stations over 50 years which makes
this pretty much anecdotal but for what it's worth:
I've never modeled them but I have used 1/4 wave verticals on 40 with
what I considered to be very good results. I've also used a pair of
them with half wave spacing, in phase and 180 degrees. Just a simple set
up as the lobes are very broad. It takes a lot of wire for the ground,
but I found that either the single vertical or the phased pair worked
great on DX. The system now is much simpler as I don't have all the
antennas up. On 40 I only have a single 40 m center fed, half wave
sloper with about a 60Deg angle plus the Hy-Gain AV640. They are both
band openers into Europe and Oceana.
I've had a number of elevated verticals with the bases at 40 feet. I
never used more than 4 quarter wave radials at an angle that gave me a
50 ohm match. The elevated vertical with these radials is not much more
than a vertical, half wave dipole.
The surprise with the 1/4 wave verticals was the reduction in QRM.
State side stations were down at least 2 S-units compared to a regular
dipole or inverted V while I could hear the DX stronger. Between the
two I could hear and work stations on the vertical I couldn't even hear
on a fairly high dipole. OTOH during thunderstorm season the QRN was
terrible if there were any TStorms out to about 5 to 600 miles. I
didn't notice much QRN from storms stateside that were farther out.
So, my experience has been *mostly* positive using 1/4 wave verticals,
arrays, and even the AV640 which is only about 30 feet from a very large
maple.
73
Roger (K8RI)
>
> 73,
> John KK9A
>
>
>
> To: towertalk@contesting.com
> Subject: [TowerTalk] trees and verticals
> From: kr2q@optimum.net
> Date: Tue, 27 Dec 2011 15:53:20 +0000 (GMT)
>
> My FYI tale of vertically polarized antennas and trees.
>
> I have always lived in very heavily wooded areas and have always used
> horizontally
> polarized antennas on the top of crankup towers. They clear the tops of
> "most"
> of
> the trees, but not all. They work REALLY WELL (I have an outstanding QTH)
> for
> DXing.
>
> Wanting to "save rotor time," while contesting (with my 402CD), I put up a
> GP
> (elevated
> vertical). It hangs from a tree. It is "full size" and has full sized
> elevated radials. My hope
> was that it would be louder than my 2L 40 when the 40 was pointed at EU (50
> degrees
> from NNJ) when I heard a new mult from the south (zone 8, 9, etc). The
> "base"
> of the GP
> is about 20 feet above ground (and so are the radials, but they slope down
> somewhat). It
> was to be my "multiplier" antenna.
>
> That was not the case. The elevated vertical (GP) is always "weak" compared
> to
> the 2L
> 40, even when the yagi is pointed at EUR and I'm comparing to the South.
> The 40m yagi is at about 80 feet.
>
> Now, I would expect the yagi to be louder to EUR as compared to the GP, but
> not
> so
> to CA/SA, which, at best, is off the back corner of the beam when beaming
> EUR.
>
> The GP vertical element is supported by the trunk of the tree, so it is
> "right
> next to" the
> tree trunk.
>
> <snip>
> de Doug KR2Q
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|