ELEMENT SPACING DOES NOT ENTER INTO EITHER GAIN OR F/B IF THE ELEMENTS ARE
PROPERLY TUNED FOR THEIR POSITION IN THE ARRAY??
Having done some antenna modeling, I find this statement difficult to
believe. Lets look at the data from SteppIR's website for their three
element yagi:
20m gain = 7.4dBi F/B = 25dB
10m gain = 9.0dBi F/B = 11dB
Since the boom is electrically double in size on 10m I would expect the gain
to be about 3dB more than on 20m. Also the F/B is 25 times better on 20m
than on 10m. Certainly with proper element spacing you can easily achieve
20 db F/B.
----- Original Message -----
From: "Joe Subich, W4TV" <w4tv@subich.com>
To: <john@kk9a.com>; <TOWERTALK@contesting.com>
Sent: Friday, May 11, 2007 10:40 PM
Subject: RE: [TowerTalk] C31XR versus SteppIR
> The SteppIR, has no element interaction problems because
> the element lengths are adjustable, however the spacing is
> not adjustable and not optimum.
This is a complete red herring ... within limits ELEMENT SPACING
DOES NOT ENTER INTO EITHER GAIN OR F/B IF THE ELEMENTS ARE PROPERLY
TUNED FOR THEIR POSITION IN THE ARRAY. It is an easy job to run a
series of models to show that an antenna of a given boom length
with have the same gain and F/B whether the inner elements are
"bunched" at the reflector end, evenly spaced or bunched at the
director end.
The feed impedance will change dramatically with spacing and
tuning of the reflector and first director. SWR bandwidth will
be effected significantly by the spacing of the reflector and
first director. However, neither of those characteristics is
of particular concern in an antenna that is mechanically tunable
like the SteppIR.
Yes, the SteppIR gives up a bit of F/B on 10 meters where the
Reflector to driven element spacing gets a bit too large. However,
it still maintains gain within 1 dB of the theoretical maximum
for a 32 foot boom yagi. Other tribanders (except for the 14' boom
three element designs) can't say that as they fail to make use of
the full boom length on every bands. Many non-trapped multi-element
multiband antennas sacrifice as much as 15 to 20% of the available
boom length on some (most?) bands.
73,
... Joe, W4TV
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of john@kk9a.com
> Sent: Friday, May 11, 2007 9:31 PM
> To: TOWERTALK@contesting.com
> Subject: Re: [TowerTalk] C31XR versus SteppIR
>
>
> I was going to ask the very same question Jay did, what is
> the protocol that
> OptiBeam does not conform to? I own one OptiBeam - an
> OB2-40 40m antenna
> and it is very well made and the customer service from Tom
> DF2BO is very
> outstanding. Regarding the subject tribanders, the C31XR is
> essentially
> three monobanders on the same boom, there are no moving
> parts, you can
> instantly change bands, and there is some element interaction
> which reduces
> the gain somewhat. The SteppIR, has no element interaction
> problems because
> the element lengths are adjustable, however the spacing is
> not adjustable
> and not optimum. It's also mechanically more complicated and
> you have to
> wait for the elements to adjust when changing bands.
> Mechanical problems do
> occur, however there are not a lot of posts on this subject
> so hopefully it
> is uncommon. I'm sure either antenna works well and it is
> up to the user
> to chose the one that best fits his operating and maintenance
> needs. If
> you want optimum performance, monobanders offer the most gain
> and make SO2R
> contesting set up very easy. For example: according to Force
> 12's catalog,
> on 15m the C31XR (31' boom) has 6.3dB gain and their EF-515X
> 15m monobander
> (30' boom) has 7.9dB gain. 6Y1V recently stated that their stacked
> monobanders were 2 to 3 S unites stronger than their stacked
> MonstIR's, of
> course some of this difference is due to different stacking
> heights which
> brings up another point. It is more difficult to stack
> multiband antennas
> and maintain the desired patteren on all bands since you
> cannot adjust the
> stacking distance.
>
> John KK9A
>
>
> To: <towertalk@contesting.com>
> Subject: Re: [TowerTalk] TowerTalk Digest, Vol 53, Issue 30
> From: "Jay Terleski" <jayt@arraysolutions.com>
> Date: Fri, 11 May 2007 18:24:30 -0500
> List-post: <mailto:towertalk@contesting.com>
>
> Currently Force 12 and SteppIR are the only manufacturers that use our
> protocol to produce useful comparable performance figures.
> If Optibeam
> figures were produced similarly, then I'd be more inclined
> to believe them.
>
>
> Cheers,
> Steve K7LXC
>
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