Antenna Polarization Switch

Introduction

PE1ITR suggested me to make a switch that would allow both horizontal, vertical, Left Hand Circular Polarization (LHCP) and Right Hand Circular Polarization (RHCP) for the 2x6 elements DK7ZB cross yagi that I made. The two antennas are mounted in a socalled 'X' configuration. Both 6 elements beams would feed into the switch with coax cables of an exact same length.

SM5BSZ has on his website several designs for electronic polarization switching. From his designs I picked one (see the picture below) and implemented the power divider as two parallel 75ohm coax lines. Two SDS S2 relays implement the four switches, see the diagram below.
     



Collected at the national HAM Radio flea-market in Rosmalen, I re-used a Kathrein chassis:


First I removed and stripped the existing PCB inside, and after cleaning up re-inserted it:


The two coax relais are both given a protection diode, de-coupling capacitors, and an LED/resistor combination for easy debug (a tip of PE1ITR):


Both relais mounted, missing still are the delay lines + the impedance transformer:


Finished design, next to the reference implementation of PE1ITR:



The results:
- I needed to reduce the length of the 75 coax lines, the optimum SWR was initially 20 MHz too low
- Resulting SWR in 145MHz band: 1:1.15
- Resulting impedance in 145MHZ band: 43 ohm
- Overall: still tuned somewhat low in frequency, but good enough

- Reception of horizontally polarized beacon:
  *vertical polarization gives higher noise level (~10db)
  *circular polarization ~3db less compared to pure horizontal (expected)
  *vertical polarization ~15db less compared to pure horizontal

- satellites: tumble and change, circular polarization has least drops in signal
- AO7 satellite: during the pass the polarization changes