Chasing down our RFI issue – success!

Spent some time with Heiko, DG1BHA, and Uwe, DL3BQA, chasing down our RFI issue this afternoon that I had reported about in my WPX-SSB blog post. Some systematic testing revealed that it’s worse with a modified TS-590 transmitting on 15 m than with an unmodified 590. But the difference was only about 7-8 dB, still no explaination for s9 QRM from unrelated frequencies! And it did not make any difference if transmitting with or without PA!

Started with bonding almost everything in our two shacks: transceivers, PAs, bandpass filters, network switches, computers, a.s.o. Something long overdue! Unfortunately it didn’t help anything! 🙁 But of course it does not hurt either and might prevent other issues. Than started to dismantle everything possible from the FLEX-6600 I’m using and suddenly there was silence, no interference anymore! I couldn’t believe it but afterwards it all makes sense. 😉

The culprit was/is my HA1YA 2 m transverter! It’s a great transverter with lots of gain, very sensitive, a.s.o. But, when the 15 m beam is pointing to the shack and Uwe’s transmitting with high power it’s coupling into the 2 m antenna (which is located on the roof above the shack) connected to the transverter and due to it’s overall gain it’s somehow overdriving the 10 m RX in the Flex. Obviously the transverter ports in the Flex are not disconnected when not using a transverter band and, probably even more important, the transverter signal is coupled into the RX behind the 7th order preselector on 10 m. We confirmed that the interference is gone switching in a 2 m (receive-only) bandpass filter before the transverter, it can then stay connected and be switched on all the time (switching it off cured the problem, too). So it’s about time to order a transmit-capable 2 m BPF and the problem is history. 😎

We still have some minor RFI issues that need to be solved but with curing this one nothing that will prevent us from doing parallel operations again. So for now quite happy!

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