CI-V Controlled Arduino Based Automatic 80m/75m ANT Switch Designed and Built by N4TD
It is generally difficult to have one antenna cover the full 3.5MHz - 4.0MHz band with low SWR and good radiation efficiency. Most one-antenna solutions achieve the increased BW by increased losses in the design which lowers the Q and increases the BW.
This switch allows automatic selection of either an 80m (fr=3.750MHz) antenna or 75m (fr=3.900MHz) antenna with a crossover at any chosen frequency. The frequency is read from the CI-V output of the IC7610. My choice of 3.830MHz for the crossover frequency is the frequency where both ANT have SWR≈1.5 and the 80m ANT SWR<3:1 for f<3.830 and the 75m ANT SWR <2:1 for 3.990MHz > f >3.830MHz.
The way it is connected to the antennas is shown here: https://w4tzb.net/antennas.html The arrangement also grounds the 80m ANT when the 75m ANT is in use, and grounds the 75m ANT when the 80m ANT is in use. Since these two antennas are both long and physically separated by only about 60ft, they interact and this switching arrangement prevents one from acting as a receiving antenna for the other and bringing RF into the shack and causing RFI.
The SPE AMB-02 controller for the SPE remote antenna switch outputs a binary code to select one of 6 antennas.
By grounding PIN1 in the DB9 connection between the controller and the relay box, the command is changed from ANT3 to ANT2.
So when the 80m/75m ANT switch senses the f < 3.830MHz then it outputs +12v which activates the AUX SWITCH to ground PIN1 and switch from the 75m antenna to the 80m antenna.
Modified: 16 November 2024