Guy -
I find your specification of 15M interaction to be misleading
and presumptious. I can understand how a FULL SIZE 40M
element would interact with 15M performance due to harmonic
relationships but not the "shorty-forties".
The 402CD is an Inductively LOADED 40M beam.
The loading coils are spaced very close to 1/2 WL at 18 MHz,
NOT 21 MHz. This is supported by the numerous reports of
satisfactory use of the 402CD on 17M with relatively low SWR.
The BOOM of the 402CD is roughly 20+ ft BUT the reflector is
BOTH electrically and mechanically attached to the Boom,
thus END loading the boom. The DE is isolated from the boom
but the COAX surely adds some capacitive coupling between
the boom and at least one side of the DE, further end loading
the boom. The 24 ft boom of my 3L20 meter beam resonates
around 7.5 MHz. Surely the 20+ ft boom of a 2L40 with 40M
elements resonates even lower, NO WHERE NEAR 15M.
SO, I find it hard to understand your statement that ANY
15M beam would be affected by the proximity of a 402CD.
de Tom N4KG
On Sun, 22 Apr 2001 "Guy Olinger, K2AV" <k2av@contesting.com> writes:
> The interaction mentioned affects ANY 15 meter beam, be it
> monobander, tribander, 5-bander, Force 12, Cushcraft, whatever brand..
The
> problem relates to whether or not the 40 meter beam has secondary
resonances
> close enough to 21 MHz to detune the 15 meter beam, which it will if
> the resonance is close enough. Even when the beam is turned at right
> angles, interaction may still remain or even be worse, due to the BOOM
of
> the 40 meter antenna being resonant on 15, or possibly other bands.
>
> It is related to the familiar ability to use a 40 meter dipole on 15
> meters at low SWR
>
> The question is whether or not the 402CD will detune the 15 meter
> beam, not the other way around. If you already own the 402CD, there's
no
> point in asking. Get your tribander of choice and prepare to possibly
> operate them at right angles, where the 402CD has been reported to work
> well.
>
> The newer XM240 has had conflicting reports in this regard, without
> any resolution that I have seen, apparently due to something in the
> newer element mounting system.
>
>
> The Force 12 x40N model 40 meter beams have their secondary
> resonance at 18 MHz due to the design of the linear loading and are
spaced
> with C31's at distances as small as 8 feet, and inline.
> There is considerable posting in the archives on the interaction
> question.
>
> 73.
> -----------------
>
> Guy Olinger
> Apex, NC, USA
>
> ----- Original Message -----
> From: "Douglas A. McDuff" <dmcduff@gate.net>
> To: <towertalk@contesting.com>
> Sent: Sunday, April 22, 2001 10:11 AM
> Subject: [TowerTalk] C31XR / CC 402CD Question
>
>
> > Before placing my order for a 31XR, I would like to know (direct
> email please) of any TT'ers experience who has/is utilizing the above
> > combination. In particular, I am interested in your experience
> with interaction, degradation, etc.
> >> > For reference, the setup here would involve the 402CD mounted 11ft
> above the 31XR.
> >
> > TIA & 73, Doug W4OX
> >
> > List Sponsor: ChampionRadio.com - Trylon self-supporting towers,
> > safety equipment, rigging gear, LOOS tension guages & more!
> > http://www.championradio.com
> >
________________________________________________________________
GET INTERNET ACCESS FROM JUNO!
Juno offers FREE or PREMIUM Internet access for less!
Join Juno today! For your FREE software, visit:
http://dl.www.juno.com/get/tagj.
List Sponsor: ChampionRadio.com - Trylon self-supporting towers,
safety equipment, rigging gear, LOOS tension guages & more!
http://www.championradio.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|