1.3GHz Transverter – separate TX / RX ports

The SG-Lab TR1300 transverter continues to impress me. My current setup on 1.3GHz is the TR1300 with Sam, G4DDK’s VLNA and a single 67 element long yagi. The Anglian transverter is used on the 144MHz IF side, both transverters are locked to a 10MHz GPSDO. Unless EME conditions are really poor, it’s unusual for the ON0EME  beacon not to be seen on the screen, albeit rather faint at times.

The TR1300 can be used with a single (SMA) antenna connection, with internal changeover switching, or by removing a SMD zero ohm resistor separate receive and transmit antenna connections can be used. To connect the VLNA and prepare for the planned SSPA I did the modification and split the antenna connections. The antenna switching is now done by an external 12V high power relay that offers ~80dB of isolation and will easily handle the planned 150W power output.

The one observation after doing this modification is that the receive path no longer has the same filtering on the input. Now this wasn’t an issue when the antenna was pointing up at The Moon but with the antenna horizontal in certain directions the band was unusable due to interference / intermodulation from strong out of band signals, due I suspect to mobile phone transmissions originating from a local base station. A search on the Internet / Microwave forums suggests this to be a fairly common problem when operating on 1.3GHz with nearby mobile phone / TV transmitters. Some additional external filtering was going to be needed.

Constructing an interdigital filter was considered, but whilst the mechanical side was doable with my (limited) workshop facilities I certainly would not have the necessary test gear to tune and measure the performance of the filter. Another local station had been experiencing a similar issue and solved it by using the KUHNE Electronic 1296 interdigital filter (MKU BPF 1.3) . This sounded as if it might work for me. So for Christmas my XYL  bought me a MKU BPF 1.3 filter … 🙂

The filter is now installed (between the VLNA and transverter RX port) and the results have met my expectations.  There is no obvious interference when looking at the band on an SDR display… and I can still “see” the ON0EME EME beacon 🙂

The following two photos show the SDR display and give an indication of the band before and after the filter was installed.

23cms before filter: heading-127deg

23cms before filter, heading-127deg

 

23cms after fitting filter, heading-127deg

23cms after fitting filter, heading-127deg

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