-
-
Notifications
You must be signed in to change notification settings - Fork 16
antennas
Considering cross dipoles to improve RX/TX isolation and allow for X/O propagation mode detection with dual receivers (future).
There are antennas designed specifically for NVIS we'll consider the gain benefits vs cost/complexity.
NVIS 5MHz: model vs. measurement
General NVIS background, antennas, SNR, etc.
To enable schools and laypersons to construct their own antennas using simple hand tools and locally-sourced, even salvaged materials, a passive multiband antenna design is proposed.
Issues with broadband dipole include low radiation efficiency
1969 SRI report is one such simple passive design. The length of this dipole will be adjusted to account for being closer to the ground that the original design may have anticipated.
The metals used in the antenna construction must be galvanically compatible or the performance will quickly degrade (and dirty interfering emissions dramatically increase) with weather exposure.
- Center support: PVC tube with mechanically robust conductive strips to connect dipole wires. Use eyebolts with appropriate mating hardware on the wires to endure windy environments while maintaining robust electrical connection.
- End supports: "egg" or "dogbone" insulators tied off via non-conductive rope to stakes, poles, fences, etc.
- dipole wire: stranded, with periodic mid-span non-conductive supports (e.g. PVC tube) to maintain proper separation between multiband wires, thereby maintaining tuned impedance. Thick enough to be durable but not so thick as to be too heavy--typically 14 gauge wires is used. Insulated or non-insulated wire may be used.