Was thinking about adding a resonant 20m element below my 125' doublet to try to overcome the lobes and nulls that are on 20m . Like adding a fan arrangement to the center of the top wire. so it would be like a hybred doublet. I feed it now with open line and no baluns, feed runs right to the balanced tuner.
Any one tried this?
73
Paul
Hi Paul,
Roughly, an open-wire fed 125' dipole tuned up on 20M is "four half waves out of phase" which will be a low impedance feed and produce a 4 lobe cloverleaf pattern. (undesirable large nulls broadside) Normally a 1/2 wave dipole bi-directional pattern would have large lobes broadside. So, you desire the 20M operation to look more like a single standard 20M dipole.
It's all about covering our best directions with fixed antennas. Here in CT, NE/SW is my favored orientations for fixed antennas.
So what you are axing is if by adding a 33' dipole to the feedpoint of the 125' dipole will the 33' dipole "hog" the power from the low impedance 125' dipole and produce the desired 2 lobe bi-directional pattern on 20M? I honestly don't know how clean the pattern will become considering both dipoles are low impedance fed - and there is a large reactive component introduced by the 125' dipole.
You will need to model it on EZNEC/ NEC4 to see just what is happening on 20M with that config. It is a good idea to consider. I would model it for you but unfortunately my new computer does not have NEC4 installed yet. Maybe someone here can do it and see if it is worth the effort to add the 20M legs.
I usually recommend separate 1/2 wave dipoles to solve the pattern problem, but maybe this will work well enough to fill in that large set of 20M broadside nulls for you.
Another solution: Use the exisiting 125' OWL dipole for 75M and 40M only. Then make up a new 20M OWL dipole (and custom tuner) and use it only for 20, 15 and 10M. You now can cover 75-10M with reasonably clean bi-directional broadside patterns on all bands. To cover 160M, a series fed config of the 125' dipole will work and be within a few dB of a regular dipole if you use heavy-duty materials for both the tuner and dipole.
Or for 160M, tie the openwire feeders together to end feed the open wire. The 125' dipole against ground will become a capacity hat. The system will then have some desirable vertical and horizontal components for general AM coverage assuming you lay down some ground radials to work against. (system is now a vertical 'T' for 160M) Verticals work especially well on 160M when set up right.
T
