[Antennas] Using Coax Traps in a rigid dipole

[JAB (EA5XQ)]

Hi,

I'm modelling with MMANA a rigid dipole for 10, 15 and 20m with the idea of=
=20
using COAX TRAPS and with the help of the VE6YP (Tony Field) Coax Trap=20
designer program.

First at all it seems that the values provided by Tony have to be changed a=
=20
little bit when used with the modeler, for instance, L has to be 4 times=20
the Inductance Tony's value, C has to be Capacitance Tony's value divided=20
by 4. Taking this in mind I was comparing the gain of this antenna with a=20
similar one (example coming with the software) but with capacitor and there=
=20
were some significant differences, from 2dBi (coax) to 7 dBi (normal). The=
=20
I was playing with the values of the L and C and I found that forcing the=20
Coax values to the normal trap I was able to get the same gain however:

1.- I need Double coax traps as what I need is a coax with high pF/m=20
(around 140)
2.- Not all the combinations L/C were optimum although all of them resonate=
=20
at the same frecuency. It seems that the values around 1.9uH of L were the=
=20
best ones for 10m and around 2.3uH for 15m

After this, that was a trial-error game, I would like to find information=20
about how to design a trap, I mean how to determine the best L for each=20
band (because C will come with the resonance frecuency) and thereafter I=20
will try to force the Double Coax Trap design with those values (bearing in=
=20
mind that an acceptable L/D ratio for a coax is between 0.45 and 2). Why=20
Double? because as far as I understood Double CoaxTrap have higher Q and=20
therefore less losses.

Coax to use? I'm thinking a RG174 that is quite light (even double)=20
compared with the RG58 (and I'm going to use not more than 150W) or a FLEX=
=20
3-75 from NORDAX which has got 70pF/m.

Any help on this, or correction if I'm wrong, will be appreciated

73s Juan, EA5XQ



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