Band isolation key to successful SO2R on multiple bands

To be able to work simultaneously on two adjacent bands like 40 and 20 m the isolation needs to be at least 90 dB. Of course this will depend on the following:

  • antenna isolation –  can be as low as 30-40 dB with close antennas or resonant antennas on harmonics.
  • antenna port isolation on the transceiver- on the Flexradio series 6000 it is about 40-50 dB between the antenna ports.

So in total an isolation that can be as low as 70-90 dB. But is this a problem? Well with a 1.5 kW station you have a signal level of around +62 dBm which is way over S9+73 dB!!! And your station can not handle more than +10-20 dBm.   To be on the safe side and also having the joy of working SO2R a good thumb of rule is at least 150 dB of isolation. This means that with a 1.5 kW station sending on say 40 m you will not have more than  S 8 (+63 – 150 dB = -87 dB) . In this exercise I have more or less ignored effects of phase noise and second harmonics (which with an old TRX can be severe).

With my set-up I end up in the following isolation between the antennas and 4o3A High Power bandpass filters (they provide about -50 dB of isolation) :





As you see about 90 dB (green lines). To this we must add the transceiver isolation of 40-50 dB. So in total 130-140 dB of isolation or S7-S9. Not too bad. That is you may send with a kW on 40 m and do listening on 20 m with a 40 m signal at about S7-S9.

My remote dx and contest station SM0HRP

Here is my remote station set-up.

New updated version of schematic.
My FlexRadio 6700 and SO2R set up with OM2500A:s.
My high bandpass filtres.



































The present antennas.

3 el 40 m yagi.


3 el 30 m yagi.


Previous XR5 stack under replacement by new JK2015 stack 4/5 on 20/15 m.


New 24 m HD tower for the JK2015 stack.

Nostalgia 3Y0X

3Y0X- SM0HRP 10.1cw  2006-02-12 about 2150z –  QRG:10104.5 KHz CW

New 24 m HD Tower project on-going with JK antenna stack.

Since Sept 2017 we have been working on configuring the new 24 m HD Alu tower that we installed just after the vacations. The mast weights about 1200 kg and is cable of 2 square meter of antenna load without any guying!

The tower will carry two JK 2015 antennas in a stack. An electric winsch that is remote controlled adds to the flexibility of the tower.