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Ghosts In The Machine-Red Pitaya CW Skimmer-Debugging BCB Interference

Many thanks to Guy, K2AV for tips, suggestions, and testing assistance to help resolve the following problems.

An unanticipated problem with fixing broken antenna systems is that it begins to work better. Well – “duh”, right?

After making repairs to the antenna switch and the 160m inv-L over the past couple of months, the antenna systems are nearing the end of a minor overhaul. Since about May, the CW Skimmer has been using a K9AY as the main RX antenna. For the period of 2 years prior it has been using the 160m Inv L as the RX antenna, until problems cropped up in May 2019[a broken connection on the feedline at the switch box.]

After correcting the broken connection and re-assembling the skimmer station, K2AV reported having spurs on harmonics when testing on 160m. Upon a closer I found several other stations for which the SDR was also generating harmonic spurs on higher bands for signals of 40-43 DB SNR into the skimmer station SDR. This was resulting in bad spots to the RBN, and as is sometimes noted “results may be unpredictable”.

All of the spurs appear to be caused by overload mixing from nearby BCB stations on 680, 850, 1360, and 1510. Some of the problem was previously handled with the BCB filter constructed with notches tuned for 680 and 850. Upon re-assemble, the BCB QRM was still sneaking in.

The bulk of the issue has been resolved by bonding the BCB filter enclosure directly […]

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