50mhz reflector
> -----Original Message-----
> From: James Hayes [SMTP:hazy119@westelcom.com]
> Sent: Sunday, March 10, 2002 2:49 PM
> To: vhf@w6yx.stanford.edu; vhfcontesting@contesting.com;
> 50mhz@topica.com; 2m@mailman.qth.net
> Subject: 50mhz Antenna Design Question
>
> 50mhz reflector
>
> Hello all on the list and please forgive the bandwidth...
>
> I'm trying to configure a couple of antenna arrays for 2M and 432. Running
> pairs of K1FO-12 for 2M and a pair of K1FO-15 for 432 in the E-plane on a
> 48
> ft tower, and while using Yagi Max I noticed that the wider the W/L
> spacing
> between the antennas the narrower the beam width of the main lobe. Most of
> the reading I've been seeing on the subject varies widely regarding the
> 'optimum' spacing.
> The original design parameters by Paul, K1FO
::I think K1FO's name is Steve.
> states one thing and YM 3.11
> states another for optimum spacing for antennas of his design. Also,
> others
> have written that .9 W/L is optimal for all arrays..
::That's obviously impossible. Who said that?
> .(confusion sets in.) I
> have noticed a tighter pattern on the main lobe provides a cleaner F/B
> ratio
> as well but it lends itself to having the antennas spaced at 1.5 W/L or
> larger!!!
::"Optimum" depends on the design and aperture of the antennas being
used. It cannot be expressed as a standard in wavelengths, and for
traditional beam antennas (yagi, quad, quagi) will never exceed the length
of the antenna booms. YO and NEC both indicate actual E & H plane patterns
for configurations entered, and you can see that closer spacings result in
somewhat reduced gain but a substantial reduction in side lobes as well,
making such arrays more optimized for e.m.e., where space noise reduces S/N
even when signals are stronger. For terrestrial work, though, the
optimum-spacing, even with the abundance of side lobes, is usually best.
> My question is rather simple...is it more desirable for one to have a
> narrower or wider bandwidth pattern on the main lobe, or is it rather a
> matter of aesthetics over gain?
::It's certainly not aesthetics, it's what you're trying to
accomplish. Eme vs. terrestrial have different objectives; then, your
operating location may drive the decision as well. For example, the
reduction in radiation angle achieved by stacking horizontal antennas one
above another is not always a noble goal, especially if you're operating
from a valley surrounded by mountains higher than your location. Then, when
operating from a mountaintop that is substantially above average terrain, a
radiation downtilt, rather than focused on the horizon, is often better (if
making contacts is the goal, and not just theoretically optimizing gain).
It can all be accurately modeled if you know the metrics.
-WB2WIK/6
> As the gain itself does not increase
> appreciably to offset the necessity of a narrower band width pattern.
>
> Jim, N2YEV
> n2yev@arrl.net
>
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