Full size element Tribandes get more and more popular. They are good by parameters, comes with different designs, cover three or more bands by a single coax line, less expensive compare to a few single band antennas and almost a perfect solution for those who limited by space to install a few towers.
Triplexer with BPFs added to the 10-15-20 band Tribander convert it into three independent antennas. Please, see a simple diagram below.
As you can see three operators can work simultaneously all three bands. Lets assume it is a Multi-Multi station. Of course, SO2R, Multi-Two or Multi-Single stations can use this setup as well (shown below).
- The drawback for such a setup shown above is that all QSOs can be made from a single direction, where Tribander rotated.
What if the second tribander added on the same tower or it installed on another tower?This way different directions for any band can be chosen (if tribanders on the same tower can be rotated independently to different directions).
Please, see the setup on a diagram below, with Triplexers dedicated to each Tribander and StackMatch units added to split power between antennas. Before Each Stack Match (SM) a band Bandpass filter added.
- With two triplexers there are six independent antennas available (two per band).
- StackMacth can divide power between Tribanders or apply all power to one Tribander, if required.
- Antennas can be rotated to the same direction or to two different directions.
- Each Stack Matсh dedicated to a single band and can be designed and built with a better parameters, like better SWR for a particular band.
For simplicity, each radios on a diagram above dedicated to a particular band but if there are only two transceiver/amplifier setup like SO2R , some switch/switches can be added to switch bands to any radio.
The last diagram is for three tribanders. On diagram below Tribanders are on separate towers but it can be a single tower with three tribanders installed one over another.
Now, there are many different band combinations can be chosen and antennas can be rotated to three different directions.
One, two or three tribanders can be chosen by any radio. Antenna switching system can be added to make it flexible to switch between radios.
In SO2R setup, one radio can use two tribanders into different directions and the 2nd radio can use all three tribanders on another band (with divided amplifier power) or use a single tribander with a full power. Many different antenna combinations can be used based on a band conditions.
Below you can see a simple diagram with only one Triplexer and one Stack Match.
I can say that I’ve never seen such an implementation but I had a discussions about such a simplified option. It looks simpler and cheaper and as a result of it some people see it as a possible conversion existing Tribander antenna stacking into SO2R setup.
It is not an easy answer and I cannot recommend such a setup now with some drawbacks has been found and written below.
I can see some drawback for such a design even without any completed field tests:
- A special more powerful Stack Match required. The applied power will be doubled if two amplifiers in action(M2 or M/S category) or tripled if three amplifiers connected (like M/M station)
- No flexibility exists for different bands. Amplifier output power distributions will be the same for all bands.
- The RX radio reception quality should be tested. Stack Match toroid and winding have no band isolation and if 20M in TX mode how good might be 15 or 10 meter band reception is under the question.
- StackMatch cannot be optimized for the particular band and as a result some higher SWRs for some bands can be expected.