First, the only one who REALLY knows about a WARC 2/2 over a C36XR is
Tom at Force 12. Send him an email.
There's a reason for that...in general this combo question involves
transmitting on 15 or 12 in proximity with a 40m antenna of some kind.
A 40 meter antenna with full size element(s) clearly has resonances on
15 m which will cause trouble. But just about all 40 m antennas are
shortened with some type of loading. This creates complex resonances
in the elements. The lumped constant (loading coil or trap) 40 m
antennas can be modelled with some difficulty, but most companies have
not published any models. The linear loaded antennas are most
difficult to model.
Either type loading, the only way to really figure out the resonances
is to transmit on the interfered frequency and see if proximity of the
loaded element "pulls" the transmitting antenna.
Tom's latest shortened 40 meter element design has a secondary
resonance at 23 point something mhz. That makes it safe for close 21
mhz antennas, but probably does something to 12 meters. That's
something that he has specifically worked on and measured.
Interactions between different brands or models no longer in
production? Forget it. Who has the money and time. Best bet is to get
busy, go back in the archives and search on your favorite antenna and
see what stuff people have posted on their combos.
Some people will say to orient the 40 at 90 degrees from the others.
Whether this works depends entirely on whether the 40 meter boom, with
any connected element(s) acting as endloading, has resonances on the
frequency(s) in question. Modelling that interaction is well beyond
nearly everyone's abilities. ANY result would have to be empirically
verified.
An example of these difficult issues can be seen in Cushcraft
upgrading their 40 meter shortened 2 element 402CD to the XM240,
presumably identical except for mechanical details. The XM240
introduced some laudable strengthening changes, remaining
"electrically identical" according to CC, but in the upgrade changed
the way the beam structure behaved in close proximity to a 15 meter
antenna.
Aren't you glad you asked?
73, y'all. Guy
On Thu, 9 Sep 1999 11:10:29 -0500, you wrote:
>Concerning destructive interaction between yagis, most of the what I have heard
>is interaction between 15 and 40 when one is over the other. The same
>frequency
>relationships don't seem to be found between 12/17 and 10-40. Has anyone
>modeled a 12/17 (like the F12 WARC 2/2) over a 10/15/20/40 (like the F12 C36XR)
>and if so how close can the two be?
>
>Thanks, Pete
73, Guy
--. .-..
Guy Olinger, K2AV
k2av@qsl.net
Apex, NC, USA
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