A friend Chazz, K7OVG, and I were talking about a problem with his Xeigu G90. I also talked with another ham having similar problem during Winter Field this year. Turns out they both have been experiencing interference when strong out of band signals were present. In my friends case it was nearby AM broadcast stations. In the other case it was another nearby ham operating on a different band. This is most likely caused by overload of the first RF amplifier in the receiver.
My friend was able to solve the problem by using an external tuner between the G90 and the antenna to act as preselector. (I know, two tuner is supposed to be a bad idea, however, desperate times call for desperate measures.) Back in the "good ol' days", it was common practice to use a preselector ahead of a receiver to solve the same problem. These devices were tunable band pass filters. One would set the receiver to the band of interest, and next set the preselector to the same band and peak the desired signals.
Chazz did the following with his G90. Selected the desired band and tuned the external tuner then pressed the tune button on the G90. He was able to stop the interference. He said he was able to transmit through both tuners without incident.
Try using just the external tuner first to see if it solves the problem. If it does the don't use the internal tuner at all.
If you try this with a different transceiver, bypass the internal tuner while you tune the external tuner. Then engage the internal tuner and let it tune. This lets the external tuner match the 50 ohm input to the transmitter. Then the internal tuner sees a 50 ohm input and adjusts to match it. Now both tuner act as bandpass filter, preselector, ahead of the first RF amp.
Another solution is to purchase preselector. Be sure if you do that there are provisions to bypass the preselector while transmitting. I looked online and found several preselector options. Most of the ones I saw were designated for SDR receivers, however, there may be something out there that has built-in transmit bypass capability.
If you try this, please let me know what you experienced. Send an email to k7pdw@arrl.net and put CSERG on the subject line.
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