EME218 VHF X-POL Switch
- EME218 Description:
Updated! June 2022 - EME218 Application Block
- Kit Constructors Alert:
- EME218 Kit Notes:
- Mounting into a Masthead Enclosure:
- VK5LO LEO Satellite Station:
- EME218 Kit Performance Tests:
- Changes and Updates:
The EME218 VHF X-POL switch has been designed to be used with two 146MHz yagi antennas mounted in a X configuration for use with the LEO Satellites. The switch allows the antennas to be switched between Vertical, Horizontal, Right Hand Circular and Left Hand Circular Polarization. Depending on the bandwidth of the antennas used, the switch will work between 144 and 148MHz for both terrestrial horizontal SSB, and vertical FM polarization. The switch will handle 200 Watts CW maximum and is mainly limited by the coaxial cable phasing lines. The switch can be simply controlled by applying an input voltage between +2 and +12vdc on the control connector inputs to switch each 12v relay.
The Antennas required need to have a very clean pattern and be very close to 50ohms. Antenna designs from DG7YBN or G0KSC are ideal. The switch relies upon the signals from each antenna arriving at the X-POL switch same time, so if one antenna is mounted in front or offset on the same boom, then compensation of one of the antennas feed line lengths will be required to add the required delay to the signal.
The PC board is designed to suit a low cost GME mast head enclosure which provides high protection of the circuitry from weather.
Top view of the EME218-2M Polarization Switch
Bottom View of the EME218-2M Polarization Switch
Side view of the EME218-2M showing how the phasing lines are routed
Side view of the EME218-2M showing how the phasing lines are routed
Side view of the EME218-2M showing how the phasing lines are routed and soldered to the board before the relays are fitted.
Side view of the EME218-2M showing how the phasing lines are routed and soldered to the board before the relays are fitted.
The Tests below show the through loss, return loss and the phase of the signals from the TRX to Antenna connectors for Vertical, Horizontal, Right Hand and Left Hand Circular polarization. The phasing lines were optimized using a DG8SAQ VNA with a 50ohm BNC termination on the unused antenna port. The phasing line lengths are slightly different than calculated and include the strip lines and relays that all affect the optimized lengths. The results indicate that the phases between the antenna connectors for the various polarizations are within a couple of degrees. Vertical is -271.85 degrees, LHCP is 1.22 degrees, Horizontal is -91.51 degrees, RHCP is 181.6 degrees.
EME218-2M TRX to ANT1 ( RL1 Off RL2 Off Vertical )
EME218-2M TRX to ANT2 ( RL1 Off RL2 Off Vertical )
EME218-2M TRX to ANT1 ( RL1 On RL2 Off LHCP )
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EME218-2M TRX to ANT2 ( RL1 On RL2 Off LHCP )
EME218-2M TRX to ANT1 ( RL1 Off RL2 On Horizontal )
EME218-2M TRX to ANT2 ( RL1 Off RL2 On Horizontal )
EME218-2M TRX to ANT1 ( RL1 On RL2 On RHCP )
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EME218-2M TRX to ANT2 ( RL1 On RL2 On RHCP )
The GME Masthead enclosure will accept cables up to around 8mm in diameter. Therefore larger cables like RG8/213 cannot be used. Larger cables would also place too much strain on the BNC sockets on the pre-amplifier board. To connect the Antenna feed line to the pre-amplifier, and pre-amplifier output to the main feed line, we recommend the use of CNT®240 ( 240 Type ) cable with crimped BNC connectors. CNT®240 is double shielded and has losses similar to RG213 cable, but has a much smaller 6mm diameter. Use the website search box and search for 240 series cable and connectors.
The EME218 board mounted in a GME Masthead Enclosure
The Enclosure has a locking Tab that holds the board firmly
