[TowerTalk] C31XR / CC 402CD Question
n4kg@juno.com
n4kg@juno.com
Mon, 23 Apr 2001 09:40:55 -0600
N4KG responses inserted throughout text below.
On Mon, 23 Apr 2001 10:02:08 -0400 "Guy Olinger, K2AV"
<k2av@contesting.com> writes:
> You might think a little about it. If it affects one fifteen meter beam
> in-line, it will affect any because the secondary resonance effect
> is on the forty meter beam, not the 15 meter beam.
Understand and agree, IF and that is a BIG IF
the 40M beam exhibits a 15M resonance.
My point is that a LOADED element does NOT
necessarily exhibit a resonance at 3X the
fundamental resonance. de N4KG
>Also please note that the
> 21 MHz resonance effect uses the ENTIRE element, behaving like three
> electrical half waves, not one,
This is true for a FULL SIZE element,
NOT TRUE for a loaded element.
de N4KG
and since the loading coil is not a 15 meter trap, the length
of the element between the coils does not control
> the secondary resonance.
I DISAGREE with the second part of that statement.
The loading coil presents an INDUCTIVE REACTANCE
at it's placement point. IF that reactance is sufficient
to isolate the end of the element, a 'resonance' will be
seen at the frequency which corresponds to 1/2 WL
at the coil spacing.
I recall reading a report where
resistors were placed in a dipole antenna and SWR
was measured at the higher 'resonance' frequency.
If I remember correctly, reasonable SWR was achieved
with around 3000 ohms of isolation from the outer
portion of the antenna.
SO, if the Loading Coil is providing more than a
few thousand ohms of reactance I suspect it does
a fairly good job of isolating the rest of the element.
de Tom N4KG
> As to factuality, a good friend here in the Raleigh area had this
> problem, and spent some serious money to have a noted east coast ham
> tower man to try all the possibilities. My friend's factual wallet
> pain on the issue, in my mind, trumps your postulations, as do quite
some
> number of posts which may be found in the archives.
Most of the reports that I recall report no problem with
the 402CD. I have seen reports of problems with the
XM240 which insulates the reflector from the boom.
One more thought. The DE of the 402CD is a SPLIT
DIPOLE. Therefore, the IMPEDANCE reflected to the
feedpoint by the unfed COAX can have an effect on the
characteristics of the DE. This reflected impedance
can be changed by changing the termination on the
unfed coax (short or open) or changing the length
of the coax. Did the "high priced tower expert" try
this approach? de N4KG
>
> I stand by my prior remarks.
>
> I will not respond to your ungentlemanly use of "presumptuous" or
> inference that I am misleading to pad some interest.
PRESUMPTUOUS: "characterized by or showing
presumption or readiness to presume in conduct
or thought"
MISLEAD: 1. "to lead or guide wrongly"
2. "to lead into error of thought"
I disagree with your conclusions and believe them
to be misleading. Presumptuous may be a bit
strong but you do seem to presume that all 402CD's
WILL affect any 15M antenna and I do not agree
with that conclusion. de Tom N4KG
> For the record, I have no financial or commercial interest in ANY of
> the antenna manufacturers. I could care less who makes the worst and
> best,> other than to avoid the one and embrace the other. I have paid
the
> going price for any antenna I have bought.
Same here. My 402CD was bought and pair for.
IMHO, it provides a good value for the money.
de Tom N4KG
Parting Question: Does anyone have a 402CD
on the ground? It would be interesting to measure
the resonances of the DE from 7 through 28 MHz.
and report them here on TowerTalk. de Tom N4KG
> -----------------
>
> Guy Olinger
> Apex, NC, USA
>
> ----- Original Message -----
> From: <n4kg@juno.com>
> To: <TOWERTALK@CONTESTING.COM>; <k2av@CONTESTING.COM>
> Sent: Monday, April 23, 2001 1:26 AM
> Subject: Re: [TowerTalk] C31XR / CC 402CD Question
>
>
> > 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