Final Ferrite Blitz

My Final Step in RFI Elimination

During the CQWW SSB Contest last week, I discovered two USB related RFI issues. Stray RF was getting into the USB serial adapter used for the Kantronics KPC-3 “Packet Communicator” TNC. I could see the USB device disconnecting/reconnecting over each TX. Stray RF was also getting into one of my APC UPS Back Up batteries, (also connected via USB) causing it to ‘bounce’ as well. The plan was to have all the cable choking done before the contest, but there was a delay. Once I had the problems sorted, I embarked on the final ferrite blitz to choke off ALL remaining unprotected cable ends.

I suppose I could just reduce power and the RFI issues would subside. But what’s the point when top output is 1.2 kw. Of course, I must have the FULL GALLON with ZERO RFI!

I heard about it on the radio!

I heard a QSO on 80m where the topic was the best prices for snap on ferrite chokes. This caught my attention quickly, as I still had a need for dozens more. In short, I learned I had overpaid for the first batch I purchased from one of the major U.S. ham dealers. For the price of 20 pieces there, I was able to buy 30 pieces at the same cost from

FAIR-RITE Mix 31 0.4" I.D. Snap On Ferrite Chokes
FAIR-RITE Mix 31 0.4″ I.D. Snap On Ferrite Chokes

I saved a few bucks and purchased 30 more pieces, enough to completely finish all the remaining cabling. Every cable in the rack is fully protected from RFI.  By using the 0.4″ I.D. ferrites, I was able to get two turns on most of them. At this point the only cables without ferrites are the ground straps! A true ferrite blitz!

I was happy to see the problem devices were not protected. Why? Because if they were protected (and still bouncing) I would likely have to relocate them.

I’ll go through high power testing again to determine if either of the trouble devices need to be physically relocated. A few trips up and down the 20 meter band at full power will duplicate the contest conditions, and should be a good indicator of whether or not the problem has been resolved. After all I’ve learned about choking cables, I’m confident I’ll find both device issues have been resolved now that they are completely choked off.

There are just enough ferrites leftover to choke off all the cabling for the upcoming 6500 transceiver installation. I also have the cables set aside for the LP-500 all choked off and ready to go as well.

I’m getting close to the top of the LP-500 waiting list!

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Author: K6HR

Licensed since 1994. Active on HF / VHF / UHF / Satellite.

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