[Antennaware] Info abt. KT34XA plus 2el 40m on same boom?

[Guy Olinger, K2AV]

[Tom's post was a non-subscriber post, if you respond you will need to
reply to him direct as well as to the list.]

Tom,

I have never heard of an interlacing solution involving an XA. There
probably is a reason for this.

Ordinary 40 meter elements have a secondary resonance at 21 MHz which
will be destructive on 15 meters, to say the least. Force 12 reduces
this problem on their 40m plus antennas with any or a combination of
three techniques:

1) placing a 40m element BEHIND all of the 20-15-10 elements, using
the front-to-back ratio of the higher band(s) antenna to reduce
unwanted interaction.

2) FOLDING (linear loading) a 40 element to move the secondary
resonance away from 21 MHz. This also performs a useful physical
SHORTENING of the 40m element tip-to-tip.

3) Adjusting non-40 meter elements to compensate for interaction.

For your problem, only 1) is straight-forward, but since an XA is
fairly long to begin with, there are non-trivial balance, weight and
stress issues. 2) is required for a problem like this, but 3) is just
about impossible given the complex design of the XA in the first
place. M Squared sells both the KT36XA and 40m monobanders that use
folded elements, but does not offer a combination antenna.

To design your own interlaced element is a complex process that
requires antenna modeling software and a lot of tower time. Force 12
was years designing their 40m multiband antennas. On a 1 to 10 scale
level of difficulty for modeling, where a dipole is a 1, designing
folded elements that add into a tribander is a 9.8.

Modeling folded elements has subtle traps where one can unknowingly
break the assumptions in the design of the program and get false
results.

In your case, many have mounted a single 40m element parallel to a
tribander boom, just above the boom, and had decent results, since the
40m dipole is elevated.

Particularly for DX, a 40m dipole up 25 meters is a rather good
antenna.

73, Guy.

----- Original Message ----- 
From: "DL2OBO Carsten Thomas Dauer" <dl2obo at parkhotelinteropa.de>
To: <antennaware at contesting.com>
Sent: Sunday, August 15, 2004 2:49 AM
Subject: [Antennaware] Info abt. KT34XA plus 2el 40m on same boom?



Hello

Thank you for reading

I have a KLM KT34XA on a 24m high crank up tower.

Is there anyone who tried to interlace a 2 element 40m Yagi on the
same boom with the KLM ? (seperate coax for the 40m section)

I can't install a seperate Yagi above the KLM because of the windload.

A Yagi below with a ringrotor is also not possible because of an 80m
4-Square which is around the tower.

I know how to calculate and build the 2 element, but I don't know how
this will influence the tribander. Has anyone ever  done this with NEC
?

Any info about this is very welcome.

TOM  DL2OBO/DF0EE