More N4KG comments inserted below.
On Wed, 17 Oct 2001 Weigl - =?iso-8859-1?Q?B=FCro?=
=?iso-8859-1?Q?_f=FCr?= Informationsvermittlung <weigl+info@magnet.at>
writes:
> The question from Jack was rather simple: ?Is it worth to move 2el
> Quad from 50 ft to 100 ft for DX??
>
> From my point of view the answer (for flat terrain) is: YES, it is
> worth the effort. But I did not say in my statement that higher is
always
> better. Here I completely aggree with Tom, N4KG who says:
>
> Higher is not always better!
>
> In contests I usually have a yagi on the tower and a dipole much
> lower (mainly to work the Europeans).
>
> If Jack has the possibility to have two antennas, one 50 ft high and
> one 100 ft high this will be better than a single antenna. If possible
> stack them on the same tower and you will have a wide range of
> possibilities (elevation angles). However usually our budget (and time)
> is limited
> and most of us are even happy to have just one tower and one antenna.
> So we have to make decisions, which should be based on available data.
Once a TALL tower is in place, it takes almost no
additional effort to install a lower antenna, especially
a simple dipole (wire or tubing) or Delta Loop.
"You can never have too many antennas" N4KG
>
> What does this mean for the question of one single antenna on one
> single tower:
>
> Yagi-Terrain shows over flat ground:
>
> The 100 ft high antenna (using a 3 el Yagi for the model) is on 14
> Mhz better for elevation angels below 14 degrees. From 14 to 28 degree
> elevation angle the 50 ft high antenna is better. The 50 ft. high
> antenna has its first (lowest) lobe at 20 degrees, the 100 ft. high at
10
> degrees.
> Analyzing the path USA (W3-Land) to Germany (DL) this means that in
> 80 % of the relative percentage of the time the 100 ft antenna is
better,
> in 16 % of the time the 50 ft antenna is better (at 4% of the time
they
> are equal). At very low angles (2 and 3°) the higher antenna is better
> by about 6 to 8 dB for 26% of the time. On the other hand the lower
> antenna may be better by 7 to 16 db (!), but this is only true for
about
> 4 percent of the time.
How was this path analysis done?
What were the assumptions?
The EARLY N6BV analysis ASSUMED
3L20's at 100 ft at BOTH ends of the path.
Not exactly representative of typical European
contest stations (the ones who run around calling us)
I don't believe he has ever modeled LOW antennas
at each end of the path. N4KG
>
> But sofar we have only have analyzed one possible path (W3 - DL) and
> one frequency. To make a decision, Jack has first to find out what kind
> of DX-operating is his major target (contesting, ragchewing with
> JA-amateurs, working the last few for DXCC...). Than he should optimize
> his antenna for it. Pete, N4ZR has given an interesting study on
comparing
> different antenna systems (Scoring your Antenna Sytem - don´t miss his
> corrections in NCJ 5/01))
>
> For a conclusion on this:
>
> 1.) Going from 0,75 lambda to 1,5 lambda for a single antenna: for
> DX it is worth the effort. But there will be situations (with a much
lesser
> probability) that 50 ft would be better!
Daytime MUF's are typically 3 times nighttime MUF's
Are you saying that 1.5 WL high is BEST at ALL times?
Not from my experience. N4KG
>
> 2.) If you have the possibilty for two antennas at different
> heights: do it! (AMEN - N4KG)
>
> 3.) If possible stack them on one tower
>
> There was one further statement from Tom, N4KG where I would like to
> add a comment:
>
> Tom says: ?The lobe at 57 degrees will not be supported by the
> ionosphere. It is also wasted energy?
>
With a 45 MHz MUF, the ionosphere will support
a 40 degree takeoff angle on 20M. I can't imagine
the MUF getting high enough to support 57 degrees
on 20M. N4KG
> Yes, it´s wasted energy for DX, but if f0 (critical frequency) is
> high enough you can have a reflection also at that lobe. At the same
> time of course, when the critical frequency is at your operating
frequency
> (3,5 or 7 Mhz for example) or higher, a lobe with 90 degrees will also
be
> reflected. Thats why we can work short distances (say some hundred
> kilometres, where we can not use the ground wave). High lobes are
> good for short distance, but of course it´s wasted energy for DX !
>
> 73s - Juergen
>
> Dipl.-Ing. Jürgen A. Weigl
> Büro für Informationsvermittlung
> Dipl.-Ingre. Jürgen & Martin Weigl
> A-8053 Graz - AUSTRIA
> Kärntner Str. 212
> Tel. 0316/28 73 50 ; Fax 0316/28 73 50-12
> http://www.tender.at
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