Linear decoupling traps
 

JN wrote:

Yes indeed, the simulation verified that my FINAL PLAN is working OK
Two very clean resonances at 3.6MHz and 10.1MHz SWR abt 1.3 on both bands
Antenna length only 26m instead of normal 41m for 80m dipole.
For the stub section I used 0.003m=3mm spacing and 1.5mm insulation on 1mm
wire DielC 2.6.

Is there any possibility in EZNEC to calculate how long is quarter WL on
10.1MHz
with these stub variables?

Not directly.

By using transmmission line objects it could have been possible to use the
VF of line 0.73.

I did run out of segments to simulate tri-band version with additional
parallel dipole.

All simulation was made in free space and probably needs some minor tuning
in real life.

EZNEC isn't able to model some radiating lines. If you use the
transmission line model, the line doesn't radiate. If you model it with
wires to allow radiation, you can use the wire insulation feature to
simulate a thin layer of insulation on the wires. This will have a small
(typically 2 - 3%) effect on the effective length of the wires as far as
common mode currents go, but very little effect on the differential
(transmission line) operation. But there's no way to model insulation
between wires, so when it has a significant effect on operation, the
analysis won't be accurate. Sometimes it's possible to separately model
the common and differential mode characteristics. For example, a folded
dipole can be modeled as a conventional dipole (for the common mode)
with transmission line model stubs across the feedpoint (representing
the differential, or transmission line mode) and a transformer for the
impedance transformation. Or a coax can be modeled as described in the
EZNEC manual. But in many cases, building such a model is difficult at
best. However, you can often get a good idea of how a system will work,
even if the actual antenna will require some adjustment compared to the
model.

Roy Lewallen, W7EL