> Since the boom is electrically double in size on 10m I would
> expect the gain to be about 3dB more than on 20m.
Gain does not double with as boom length doubles ... never did,
never will. If it did a Hy-gain 105BA would have 3 dB more gain
that a 204BA. The actual increase from doubling the boom length
is in the 1.5 to 2 dB range and consistent with the difference
in SteppIR's 20 and 10 meter numbers.
> 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.
Sure - but with a four element antenna on 10 meters if you want
to maintain 20 dB F/R the maximum boom length is going to be in
the 18 to 20 foot range. To get 20+ dB F/R on a 32 foot boom
takes at least 5 elements on 10 meters and that's a completely
different antenna.
Multi-element aluminum antennas give up gain by adding reflectors
closer to the driven element (shorter effective boom) and adding
extra close spaced directors that need to be detuned on the other
bands.
73,
... Joe, W4TV
> -----Original Message-----
> From: john@kk9a.com [mailto:john@kk9a.com]
> Sent: Sunday, May 13, 2007 11:18 AM
> To: TOWERTALK@contesting.com
> Cc: Joe Subich, W4TV
> Subject: Re: [TowerTalk] C31XR versus SteppIR
>
>
> 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
> >
>
>
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|